physiology signal transduction and protein synthesis
TRANSCRIPT
PHYSIOLOGYPHYSIOLOGY
Signal Transduction and Protein Signal Transduction and Protein SynthesisSynthesis
DNADNA
DNADNA– Deoxyribonucleic AcidDeoxyribonucleic Acid– Twisted ladder or double helixTwisted ladder or double helix– NucleotidesNucleotides
» Composed of alternating sugar (Deoxyribose) and Composed of alternating sugar (Deoxyribose) and phosphate molecules andphosphate molecules and
» Nitrogen basesNitrogen bases Purines = adenine and guaninePurines = adenine and guanine Pyrimidines = thymine cytosinePyrimidines = thymine cytosine
DNADNA
Purines bond with PyrimidinesPurines bond with Pyrimidines– Complementary base pairsComplementary base pairs
» Adenine with ThymineAdenine with Thymine
» Guanine with CytosineGuanine with Cytosine
DNADNA
Purines bond with PyrimidinesPurines bond with Pyrimidines– Complementary base pairsComplementary base pairs
» Adenine with ThymineAdenine with Thymine
» Guanine with CytosineGuanine with Cytosine
NucleosideNucleoside– Sugar bonding with a baseSugar bonding with a base
NucleotideNucleotide– Adding a phosphate to a nucleosideAdding a phosphate to a nucleoside
Phosphates attach to the 5Phosphates attach to the 5’’ carbon of the sugar carbon of the sugar
Orientation of DNA Orientation of DNA
The directionality of a DNA strand is due to the The directionality of a DNA strand is due to the orientation of the phosphate-sugar backbone.orientation of the phosphate-sugar backbone.
The carbon atoms on the sugar ring are numbered for reference. The 5’ and 3’ hydroxyl groups (highlighted on the left) are used to attach phosphate groups.
DNA is a double helixDNA is a double helix
P
A
P C
P
G
P T
P C
P
G
P
A
PC
PT
G
P
PC
P
A sugar and phosphate “backbone” connects nucleotides in a chain.
P
G
P
Two nucleotide chains together wind into a helix.
DNA strands are antiparallel.
DNA has directionality.
5’
3’
3’
5’
Hydrogen bonds between paired bases hold the two DNA strands together.
DNADNA
A chromosomeA chromosome
– 23 pair = diploid23 pair = diploid
– 23 = haploid; sex cells23 = haploid; sex cells– Duplicating DNA structure tightly packed Duplicating DNA structure tightly packed
around histone proteins to form a nucleosome.around histone proteins to form a nucleosome.
DNADNA
A geneA gene– A series of bases that occupy a specific location (locus) on a A series of bases that occupy a specific location (locus) on a
chromosomechromosome– The code of a single protein or polypeptideThe code of a single protein or polypeptide
Genetic AlphabetGenetic Alphabet– Triplet = Three nucleotides on DNA with their corresponding base Triplet = Three nucleotides on DNA with their corresponding base
pairs making up the code of a single amino acidpairs making up the code of a single amino acid– Codon = Three successive nucleotides on RNA with their Codon = Three successive nucleotides on RNA with their
corresponding base pairs making up the code of a single amino corresponding base pairs making up the code of a single amino acidacid
– 20 amino acids20 amino acids– A series of amino acids makes up a proteinA series of amino acids makes up a protein
DNADNA
Consists of 3 billion base pairsConsists of 3 billion base pairs– Codes for about 50 to 100,000 genesCodes for about 50 to 100,000 genes– Genes may exist in alternate forms = allelesGenes may exist in alternate forms = alleles
» One allele from mom and one allele from dadOne allele from mom and one allele from dad
– Nucleotide changes or mutations may occur in a geneNucleotide changes or mutations may occur in a gene» Sickle cell anemia Sickle cell anemia
– In a healthy population, a gene may exist in multiple In a healthy population, a gene may exist in multiple allelesalleles
– Genetic Polymorphism = Multiple different forms at a Genetic Polymorphism = Multiple different forms at a gene locus in a population gene locus in a population
» Basis for DNA typing using MHCBasis for DNA typing using MHC
TerminologyTerminology
– AlleleAllele» An alternate form of a geneAn alternate form of a gene
– LocusLocus» Location of a gene on a chromosomeLocation of a gene on a chromosome
– GeneGene» Genetic code or Genetic code or ““blueprintblueprint”” for the cell to build one for the cell to build one
particular proteinparticular protein
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Two types of nucleic acidsTwo types of nucleic acids
RNARNAUsually single-strandedUsually single-stranded
Has uracil as a baseHas uracil as a base
Ribose as the sugarRibose as the sugar
Carries Carries proteinprotein-encoding -encoding informationinformation
Can be catalyticCan be catalytic
DNADNAUsually double-strandedUsually double-stranded
Has thymine as a baseHas thymine as a base
Deoxyribose as the sugarDeoxyribose as the sugar
Carries Carries RNARNA-encoding -encoding informationinformation
Not catalyticNot catalytic
Proteins are necessary for cell functionsProteins are necessary for cell functions
Protein synthesis is under nuclear direction Protein synthesis is under nuclear direction DNA specifies ProteinsDNA specifies Proteins
Protein SynthesisProtein Synthesis
DNA DNA mRNA mRNA Protein Protein? ?
1 start codon1 start codon
3 stop codon3 stop codon
60 other codons for 19 aa60 other codons for 19 aa
Redundancy of Genetic Code (p 115)
A combination of three bases forms a codon
RNARNA
DefinitionsDefinitions– ExonExon
» Amino acid specifying informational sequences in Amino acid specifying informational sequences in the genes of higher organismsthe genes of higher organisms
– IntronIntron» Noncoding segments or portions of DNA that Noncoding segments or portions of DNA that
ranges from 60 to 100,000 nucleotides longranges from 60 to 100,000 nucleotides long
TranscriptionTranscription
DNADNA is transcribed into is transcribed into complementary complementary mRNAmRNA
byRNA PolymeraseRNA Polymerase
+ nucleotides+ Mg2+
+ ATP
Gene = elementary unit of inheritance
Compare to Fig. 4-33
TranscriptionTranscription
First steps in protein synthesis that occurs First steps in protein synthesis that occurs completely within the nucleuscompletely within the nucleus
DNA is used as a template to create a small DNA is used as a template to create a small single strand of mRNA that can leave single strand of mRNA that can leave through the nuclear pore.through the nuclear pore.
The enzyme The enzyme RNA polymeraseRNA polymerase plus plus magnesium or manganese ionsmagnesium or manganese ions along with along with ATPATP are needed in this process. are needed in this process.
TranscriptionTranscriptionDNA is used as a template for creation of RNA DNA is used as a template for creation of RNA
using the enzyme RNA polymerase.using the enzyme RNA polymerase.
DNA
5’
3’
5’
3’
G T C A T T C G G
C A G T A A G C C
TranscriptionTranscriptionThe new RNA molecule is formed by incorporating The new RNA molecule is formed by incorporating
nucleotides that are complementary to the template strand.nucleotides that are complementary to the template strand.
DNA coding strand
DNA template strand
DNA
5’
3’
5’
3’
G T C A T T C G G
C A G T A A G C C
G
RNA
5’
GG U C A U U C
3’
TranscriptionTranscription
PromoterPromoter
– Sequence on DNA where the RNA Sequence on DNA where the RNA polymerase attaches to begin polymerase attaches to begin transcriptiontranscription
– A region at the beginning of a gene that must A region at the beginning of a gene that must be activated before transcription can begin.be activated before transcription can begin.
– This region is not transcribed into mRNAThis region is not transcribed into mRNA
TranscriptionTranscription
Transcription FactorsTranscription Factors– Binds to DNA and activates the promoterBinds to DNA and activates the promoter
» Tells the RNA polymerase where to bind to the DNATells the RNA polymerase where to bind to the DNA
» RNA polymerase moves along the DNA molecule and RNA polymerase moves along the DNA molecule and ““unwindsunwinds”” the double strand by breaking hydrogen bonds the double strand by breaking hydrogen bonds between base pairsbetween base pairs
– Sense strandSense strand» Guides RNA polymerase in RNA synthesisGuides RNA polymerase in RNA synthesis
– Antisense strandAntisense strand» Sits idly by and is not transcribedSits idly by and is not transcribed
TranscriptionTranscription
Each base of the DNA sense strand pairs Each base of the DNA sense strand pairs with a complementary mRNA basewith a complementary mRNA base– AGTAC on DNAAGTAC on DNA– UCAUG on mRNAUCAUG on mRNA
Uracil is substituted for ThymineUracil is substituted for Thymine Ribose sugar is used as the backbone of Ribose sugar is used as the backbone of
mRNA instead of Deoxyribose sugar mRNA instead of Deoxyribose sugar
TATA binding protein
Initiation of transcriptionInitiation of transcription
DNA GG TATA CCC
Transcription begins
Promoter Gene sequence to be transcribed
TATA box
Transcription begins at the 5’ end of the gene in aregion called the promoter.
The promoter recruits TATA protein, a DNA binding protein, which in turn recruits other proteins.
Transcription factor
mRNA processingmRNA processing
Alternative splicing occursAlternative splicing occurs– Enzymes clip segments out of the middle or off Enzymes clip segments out of the middle or off
the ends of mRNA strandsthe ends of mRNA strands» IntronsIntrons
– mRNA segments are spliced back together by mRNA segments are spliced back together by the spliceozyme enzymethe spliceozyme enzyme
» ExonsExons
The processes mRNA leaves through the The processes mRNA leaves through the nuclear pore and attaches to a ribosomenuclear pore and attaches to a ribosome
mRNAmRNA
Contains the coded information for the Contains the coded information for the amino acid sequence of a proteinamino acid sequence of a protein
3 main parts:3 main parts:– 5' leader sequence - important for the start of 5' leader sequence - important for the start of
protein synthesis.protein synthesis.– Coding Sequence - the sequence that codes for Coding Sequence - the sequence that codes for
the amino acid.the amino acid.– 33’’ trailer sequence - poly A tail. trailer sequence - poly A tail.
Messenger RNA undergoes three (or Messenger RNA undergoes three (or four) four) post-transcriptionalpost-transcriptional
modificationsmodifications
1. Capping of 51. Capping of 5’’ end end
2. Additional of poly A tail to 32. Additional of poly A tail to 3’’ end end
3. Removal of introns3. Removal of introns
4. Editing of RNA (rarely)4. Editing of RNA (rarely)
EUKARYOTES ONLY!!!!!!!!!!!!!!!!EUKARYOTES ONLY!!!!!!!!!!!!!!!!
55’’ capping. capping.
Involves the addition of a guanine (usually 7-methyl-Involves the addition of a guanine (usually 7-methyl-guanosine) to the terminal 5guanosine) to the terminal 5’’ nucleotide. nucleotide.
The enzyme that completes this process is called a The enzyme that completes this process is called a capping enzymecapping enzyme..
The 5The 5’’ cap is required for the ribosome to bind to the cap is required for the ribosome to bind to the mRNA as the initial step of translation.mRNA as the initial step of translation.
Addition of a 3Addition of a 3’’poly A tail.poly A tail. This poly(A) tail is usually about 50 - 250 bps of adenine in This poly(A) tail is usually about 50 - 250 bps of adenine in
length.length. There is no DNA template for this tail?There is no DNA template for this tail? Poly A tails are found on most mRNA molecules but not all Poly A tails are found on most mRNA molecules but not all
(ex. histones mRNA have no poly A tail).(ex. histones mRNA have no poly A tail). In general, a eukaryotic mRNA molecule is longer than the In general, a eukaryotic mRNA molecule is longer than the
required transcript. The enzyme RNA endonuclease cleaves required transcript. The enzyme RNA endonuclease cleaves the molecule at the poly(A) addition site to generate a 3the molecule at the poly(A) addition site to generate a 3’’ OH OH end.end.
The poly A tail is important for determining the stability of the The poly A tail is important for determining the stability of the mRNA molecule so the mRNA doesnmRNA molecule so the mRNA doesn’’t degrade.t degrade.
TranslationTranslation
Translation begins when mRNA binds to a Translation begins when mRNA binds to a ribosome in the cytoplasm of the cell.ribosome in the cytoplasm of the cell.
TranslationTranslationmRNA is translated into string of aa mRNA is translated into string of aa (= polypeptide)(= polypeptide)
mRNA + ribosomes + tRNA meet in cytoplasm
Anticodon pairs with mRNA codon aa determined
Amino acids are linked via peptide bond.
2 important components ??
The Genetic CodeThe Genetic Code
The code has start and stop signals.The code has start and stop signals.AUG (methionine) is the common AUG (methionine) is the common start codonstart codonMethionine can also be used WITHIN a Methionine can also be used WITHIN a
polypeptidepolypeptideGUG may also be used as a start codon.GUG may also be used as a start codon.
There are three stop codons.There are three stop codons.UAGUAGUAAUAAUGA UGA
All three are chain termination codons.All three are chain termination codons.
Ribosomal RNARibosomal RNA
Large and small subunitsLarge and small subunits Binding sitesBinding sites
– One for mRNAOne for mRNA– Three for tRNAThree for tRNA
» P site = Peptidyl-tRNA siteP site = Peptidyl-tRNA site
» A site = Aminoacyl-tRNA siteA site = Aminoacyl-tRNA site
» E site = Exit siteE site = Exit site
Transfer RNATransfer RNA
The correct amino acid is added to the The correct amino acid is added to the growing polypeptide only if:growing polypeptide only if:– 1 - The appropriate amino acid is added to the 1 - The appropriate amino acid is added to the
tRNA by aminoacyl-tRNA synthetases.tRNA by aminoacyl-tRNA synthetases.– 2 – Complementary binding occurs between the 2 – Complementary binding occurs between the
codon of the mRNA and the anticodon of the codon of the mRNA and the anticodon of the tRNA.tRNA.
Translation (An Overview)Translation (An Overview)
Translation is defined as protein synthesis.Translation is defined as protein synthesis. Occurs on ribosomes, where the genetic information Occurs on ribosomes, where the genetic information
is translated from the mRNA to a protein.is translated from the mRNA to a protein. mRNA is translated in the 5mRNA is translated in the 5’’ to 3 to 3’’ direction. direction. Amino acids are brought to the ribosome bound to a Amino acids are brought to the ribosome bound to a
specific tRNA molecule.specific tRNA molecule. The mRNA and tRNA are responsible for the correct The mRNA and tRNA are responsible for the correct
recognition of each amino acid in the growing recognition of each amino acid in the growing polypeptidepolypeptide
InitiationInitiation
A small ribosomal subunit binds to both A small ribosomal subunit binds to both mRNA at the 5mRNA at the 5’’ cap along with a specific cap along with a specific initiator tRNAinitiator tRNA– The initiator tRNA carries methionineThe initiator tRNA carries methionine
tRNAtRNA’’s anticodon binds with the codon on s anticodon binds with the codon on mRNAmRNA
The large ribosomal subunit attaches to form The large ribosomal subunit attaches to form the the translation initiation complex.translation initiation complex.
The initiation complex is held together by The initiation complex is held together by proteins called proteins called initiation factorsinitiation factors
InitiationInitiation
The tRNA sits in the P site of the ribosomeThe tRNA sits in the P site of the ribosome The A site is vacantThe A site is vacant The methionine is at the N-terminus of the The methionine is at the N-terminus of the
growing proteingrowing protein The carboxyl end is called the C-terminusThe carboxyl end is called the C-terminus All proteins grow from the N to the C-All proteins grow from the N to the C-
terminusterminus
ElongationElongation Binding of the aminoacyl-tRNA to the ribosomeBinding of the aminoacyl-tRNA to the ribosome
formation of a peptide bondformation of a peptide bond
The movement (translocation) of the ribosome along The movement (translocation) of the ribosome along the mRNA, one codon at a time.the mRNA, one codon at a time.
ElongationElongation
Three step cycleThree step cycle– The ribosome will move 5The ribosome will move 5’’ to 3 to 3’’ on the mRNA on the mRNA
Step oneStep one– The anticodon of an incoming aminoacyltRNA The anticodon of an incoming aminoacyltRNA
base-pairs with the complementary mRNA codon base-pairs with the complementary mRNA codon in the A sitein the A site
– GTP hydrolysis occursGTP hydrolysis occurs
ElongationElongation
Step twoStep two– The large ribosomal subunit catalyzes the formation of a The large ribosomal subunit catalyzes the formation of a
peptide bondpeptide bond– Hydrogen bonds break between the t-RNA in the P site and Hydrogen bonds break between the t-RNA in the P site and
between the codon and anti-codonbetween the codon and anti-codon Step three – translocationStep three – translocation
– The ribosomes moves along the mRNA one codon The ribosomes moves along the mRNA one codon – The tRNA that was in the A site is now in the P siteThe tRNA that was in the A site is now in the P site– The tRNA in the P site exits through a tunnel in the rRNA The tRNA in the P site exits through a tunnel in the rRNA
called the E sitecalled the E site– The next tRNA enters in the empty A siteThe next tRNA enters in the empty A site
TerminationTermination
Termination is usually signaled by one of the Termination is usually signaled by one of the three stop codons UAG, UAA or UGA.three stop codons UAG, UAA or UGA.
There are a number of There are a number of ““helperhelper”” proteins proteins involved (e.g. termination factors and release involved (e.g. termination factors and release factors).factors).
GTP is necessary to break the complex apartGTP is necessary to break the complex apart
Translation initiationTranslation initiation
Leadersequence
mRNA
5’ 3’
mRNA
A U GU U C G U C G G A C G AU G U A A G A
Small ribosomal subunit
Assembling to begin translation
Met
U A C
Initiator tRNA
Translation ElongationTranslation Elongation
CU A
Met
mRNA5’ 3’
Amino acidLarge ribosomal subunit
C C U
tRNA
Ribosome
Gly
U U U CG G G G GGA A A A A
P A
Translation ElongationTranslation Elongation
CU A
Met
mRNA5’ 3’
C C U
Gly
U U U CG G G G GGA A A A A
AAC
Cys
P
A
Translation ElongationTranslation Elongation
mRNA5’ 3’
Met
A AC
Cys
C C U
Gly
C
UA
U U U CG G G G GGA A A A A
P A
Translation ElongationTranslation Elongation
mRNA5’ 3’
Met
A AC
Cys
C
UU
Lys
C C U
Gly
U U U CG G G G GGA A A A A
CU
A
P A
Translation ElongationTranslation Elongation
mRNA5’ 3’
CC
U
MetGly
CU U
Lys
Lengtheningpolypeptide(amino acid chain)
A AC
Cys
U U U CG G G G GGA A A A A
P A
Translation ElongationTranslation Elongation
mRNA5’ 3’
MetGly
C UG
Arg
CU U
Lys
A AC
Cys
U U U CG G G G GGA A A A AC
CU
P A
Translation ElongationTranslation Elongation
mRNA5’ 3’
MetGly
C UG
Arg
CU U
Lys
A AC
Cys
U U U CG G G G GGA A A A AC
CU
P
A
Translation ElongationTranslation Elongation
mRNA5’
U U U CG G G G GGA A A A A U A A
Stop codon
C UG
Arg
CU U
Lys
MetGly
Cys
Releasefactor
A
AC
P
A
Translation TerminationTranslation Termination
mRNA5’
CU
U
Met Gly CysLys
Stop codonRibosome reaches stop codon
C UG
Arg
U U U CG G G G GGA A A A A U A A
ReleasefactorP
A
Translation TerminationTranslation Termination
UU U
CG G G G G
GAA A A A U A A
C UG
MetGly
CysLys
Arg
Releasefactor
Once stop codon is reached, elements disassemble.
P
A
Translation ModificationsTranslation Modifications
Protein foldingProtein folding GlycosylationGlycosylation
– Addition of glycogen to the protein by the Addition of glycogen to the protein by the Golgi ApparatusGolgi Apparatus
– Create a glycoproteinCreate a glycoprotein VesiculationVesiculation
– Protein is surrounded by a vesicle Protein is surrounded by a vesicle Exocytosis will then occurExocytosis will then occur
Protein SortingProtein Sorting No signal sequence No signal sequence protein stays in cellprotein stays in cell
Signal sequence Signal sequence protein destined for translocation into protein destined for translocation into organelles or organelles or for export for export
Post – Translational protein modifications: Folding, cleavage, additions glyco- , lipo- proteins
Modifications in ERModifications in ER
Transition vesicles toTransition vesicles to
Golgi apparatus for further Golgi apparatus for further modificationsmodifications
Transport vesicles to cell Transport vesicles to cell membranemembrane
For For ““export proteinsexport proteins””: Signal sequence leads : Signal sequence leads growing polypeptide chain across ER membrane growing polypeptide chain across ER membrane
into ER lumeninto ER lumen
Signal TransductionSignal Transduction
11stst The signal molecule is a ligand that binds to a The signal molecule is a ligand that binds to a receptor. The ligand is also known as the first receptor. The ligand is also known as the first messenger because it brings information to its messenger because it brings information to its target celltarget cell
22ndnd Ligand-receptor binding activates the receptor Ligand-receptor binding activates the receptor33rd rd The receptor in turn activates one or more The receptor in turn activates one or more
intracellular signal moleculesintracellular signal molecules44thth the last signal molecule in the pathway initiates the last signal molecule in the pathway initiates
synthesis of target proteins or modifies existing synthesis of target proteins or modifies existing target proteins to create a responsetarget proteins to create a response
Receptor ProteinsReceptor Proteins
Lipophilic signal moleculesLipophilic signal molecules– Can diffuse through the phospholipid bilayer Can diffuse through the phospholipid bilayer
and bind to cytosolic receptors or nuclear and bind to cytosolic receptors or nuclear receptorsreceptors
– Steroids are lipophilicSteroids are lipophilic Lipophobic signal moleculesLipophobic signal molecules
– Unable to diffuse through the phospholipid Unable to diffuse through the phospholipid bilayer of the cellbilayer of the cell
– Bind to receptor proteins on the cell membraneBind to receptor proteins on the cell membrane
Receptor-EnzymesReceptor-Enzymes
Transmembrane receptor binds with a ligand on Transmembrane receptor binds with a ligand on the extracellular surface of the cellthe extracellular surface of the cell
Intracellularly an enzyme is bound to the receptor Intracellularly an enzyme is bound to the receptor proteinprotein– The enzyme is typically a protein kinase (ie. tyrosin The enzyme is typically a protein kinase (ie. tyrosin
kinase) or guanylyl cyclasekinase) or guanylyl cyclase
– Guanylyl cyclase converts GTP to cyclic GMP (cGMP)Guanylyl cyclase converts GTP to cyclic GMP (cGMP)
– Adenylyl cyclase converts ATP to cyclic AMP (cAMP)Adenylyl cyclase converts ATP to cyclic AMP (cAMP)
Signal TransductionSignal Transduction
The process by which an extracellular The process by which an extracellular signal molecule activates a membrane signal molecule activates a membrane receptor that in turn alters intracellular receptor that in turn alters intracellular molecules to create a responsemolecules to create a response
Signal AmplificationSignal Amplification
Turns on signal molecules into multiple Turns on signal molecules into multiple second messenger moleculessecond messenger molecules
Steps of Signal TransductionSteps of Signal Transduction
An extracellular signal molecule binds to An extracellular signal molecule binds to and activates a protein or glycoprotein and activates a protein or glycoprotein membrane receptormembrane receptor
The activated membrane receptor turns on The activated membrane receptor turns on its associated proteinsits associated proteins– The proteins may activate protein kinasesThe proteins may activate protein kinases– The proteins may create an intracellular second The proteins may create an intracellular second
messengermessenger
Second MessengerSecond Messenger
Second messenger moleculesSecond messenger molecules– Alter the ion channels by opening or closing Alter the ion channels by opening or closing
themthem– Increase intracellular calcium in order for the Increase intracellular calcium in order for the
calcium to bind to proteins and change their calcium to bind to proteins and change their functionfunction
– Change enzyme activityChange enzyme activity
Signal molecule binds to the G-protein linked Signal molecule binds to the G-protein linked receptorsreceptors– The protein changes confirmation and activates the The protein changes confirmation and activates the
intracellular G proteinintracellular G protein The G protein moves horizontally in the The G protein moves horizontally in the
membrane to bind with adenylyl cyclase, an membrane to bind with adenylyl cyclase, an amplifier enzymeamplifier enzyme
Adenylyl cyclase converts ATP to cyclic AMPAdenylyl cyclase converts ATP to cyclic AMP cAMP activates protein kinase AcAMP activates protein kinase A Protein kinase A phosphorylates other proteinsProtein kinase A phosphorylates other proteins
– There is a cellular responseThere is a cellular response» Such as a protein binding to the promoter site on DNA to start Such as a protein binding to the promoter site on DNA to start
transcriptiontranscription» Release of calcium to change enzyme activityRelease of calcium to change enzyme activity
Specificity v CompetitionSpecificity v Competition
Receptors have binding sites for ligandsReceptors have binding sites for ligands– Different molecules may be able to bind to the Different molecules may be able to bind to the
same receptorsame receptor» Ie. Epinephrine and its cousin NorepinephrineIe. Epinephrine and its cousin Norepinephrine
These both bind to a class of receptors called Adrenergic These both bind to a class of receptors called Adrenergic receptorsreceptors
– Alpha and Beta receptorsAlpha and Beta receptors» Alpha has a higher affinity for norepinephrineAlpha has a higher affinity for norepinephrine
» B2 receptors have a higher affinity for epinephrineB2 receptors have a higher affinity for epinephrine
Agonists v AntagonistsAgonists v Antagonists
When a ligand combines with a receptorWhen a ligand combines with a receptor– Either the ligand turns the receptor on and Either the ligand turns the receptor on and
elicits a response orelicits a response or– The ligand occupies the binding site and The ligand occupies the binding site and
prevents a response from happeningprevents a response from happening Agonist – turns receptors Agonist – turns receptors ““onon”” Antagonist – turns receptors Antagonist – turns receptors ““offoff””
Which of the following Which of the following nucleotide bases in DNA can nucleotide bases in DNA can form H-bonds with the base form H-bonds with the base
adenine?adenine? A.A. ThymineThymine
B.B. UracilUracil
C.C. GuanineGuanine
D.D. Cytosine Cytosine
E.E. Both A and BBoth A and B
Which of the following Which of the following nitrogennitrogen bases are purines?bases are purines?
A.A. Uracil and GuanineUracil and Guanine
B.B. Adenine and ThymineAdenine and Thymine
C.C. Guanine and CytosineGuanine and Cytosine
D.D. Cytosine and AdenineCytosine and Adenine
E.E. Adenine and GuanineAdenine and Guanine
How many pair of chromosomes How many pair of chromosomes are found in a diploid cell?are found in a diploid cell?
A.A. 88
B.B. 1616
C.C. 2323
D.D. 4646
E.E. 00
DNA is formed by hydrogen DNA is formed by hydrogen bonding two antiparallel strands.bonding two antiparallel strands.
A.A. TrueTrue
B.B. FalseFalse
In which direction is a DNA In which direction is a DNA strand read?strand read?
A.A. 55’’ to 3 to 3’’
B.B. 33’’ to 5 to 5’’
C.C. 33’’ to 3 to 3’’
D.D. 55’’ to 5 to 5’’
In DNA, guanine is bonded to In DNA, guanine is bonded to cytosine bycytosine by
A.A. ionic bondingionic bonding
B.B. coordinate covalent bondingcoordinate covalent bonding
C.C. covalent bondingcovalent bonding
D.D. hydrogen bondinghydrogen bonding
A gene can best be defined as:A gene can best be defined as:
A.A. Three base triplet that specifies a particular Three base triplet that specifies a particular amino acidamino acid
B.B. Non-coding segments of DNA up to 100,000 Non-coding segments of DNA up to 100,000 nucleotides long.nucleotides long.
C.C. A segment of DNA that carries the A segment of DNA that carries the instructions for one polypeptide chain.instructions for one polypeptide chain.
D.D. An RNA messenger that codes for a particular An RNA messenger that codes for a particular polypeptide.polypeptide.
If the nucleotide or base sequence of the DNA If the nucleotide or base sequence of the DNA strand used as a template for messenger RNA strand used as a template for messenger RNA
synthesis is ACGTT, then the sequence of synthesis is ACGTT, then the sequence of bases in the corresponding mRNA would be:bases in the corresponding mRNA would be:
A.A. TGCAATGCAA
B.B. ACGTTACGTT
C.C. UGCAAUGCAA
D.D. GUACCGUACC
In DNA, complementary base pairing occurs In DNA, complementary base pairing occurs between _______________between _______________
A.A. Cytosine and thymineCytosine and thymine
B.B. Adenine and guanineAdenine and guanine
C.C. Thymine and uracilThymine and uracil
D.D. Guanine and cytosineGuanine and cytosine
Messenger RNAMessenger RNA
A.A. is composed of two nucleotide chains is composed of two nucleotide chains similar to DNAsimilar to DNA
B.B. is a very stable molecule; that is, it is not is a very stable molecule; that is, it is not easily broken downeasily broken down
C.C. transfers genetic information from DNA transfers genetic information from DNA molecules to the ribosomemolecules to the ribosome
D.D. is synthesized on the ribosomes in the is synthesized on the ribosomes in the cytoplasmcytoplasm
TranscriptionTranscription
A.A. Occurs on the surface of the ribosomeOccurs on the surface of the ribosome
B.B. Is the final process in the assembly of a Is the final process in the assembly of a proteinprotein
C.C. Occurs during the synthesis of any type of Occurs during the synthesis of any type of RNA by use of a DNA templateRNA by use of a DNA template
D.D. Is catalyzed by DNA polymeraseIs catalyzed by DNA polymerase
___________ is an enzyme that breaks the ___________ is an enzyme that breaks the hydrogen bonds on DNA to begin the process hydrogen bonds on DNA to begin the process
of transcriptionof transcription
A.A. DNA polymeraseDNA polymerase
B.B. RNA polymeraseRNA polymerase
C.C. LipaseLipase
D.D. PhenylketonurinasePhenylketonurinase
E.E. AldolaseAldolase
The genetic code on mRNA for The genetic code on mRNA for methionine ismethionine is
A.A. AUGAUG
B.B. AUCAUC
C.C. UAGUAG
D.D. UACUAC
Where on DNA does cAMP Where on DNA does cAMP bind?bind?
A.A. Initiator siteInitiator site
B.B. Promoter sitePromoter site
C.C. DNA binding siteDNA binding site
D.D. TATA boxTATA box
