nucleic acids: the molecules of life. dna and rna both are polymers. they are made up of monomers...
TRANSCRIPT
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Nucleic Acids:
The Molecules of Life
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DNA and RNA
Both are polymers.
They are made up of monomers called ______________
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phosphate sugar base
CH2
OC
C C
C
O
O
O
OP
-
-
N1’
2’3’
4’
5’
OH OH
• Nucleotides have three parts to them: • a _____________• b _____________• c _____________
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_____________ bonding…
• Joins nucleotides together• ____________ reaction• Eliminates ____ molecule
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PBASESugar
PBASESugar
PBASESugar
PBASESugar
PBASESugar
Adenine
Guanine
Cytosine
Thymine
BASE
BASE
Thymine
Adenine
Thymine
BASE
Cytosine
BASEGuanine
BASEAdenine
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The Bases
• ________: thyminecytosine
• _______: adenineguanine
RNA has URACIL instead of thymine
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Base pairing…
• Complementary base pairing
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DNA REPLICATIONWhen cells divide, you need to have 2 copies of the DNA in the cell
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DNA Replication
• Most important feature of DNA is its ability to replicate itself, (almost) exactly
• The double helix is ‘unzipped’ during replication
• New nucleotides are aligned along the DNA strands (built by DNA polymerase)
• The new helix contains one original strand and one new strand
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1
2
3
4
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Semi - conservative replication – Meselson & Stahl
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Ribonucleic Acid (RNA) & its role in Protein synthesis
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The structure of ribonucleic acid
• Learning Objectives:– Describe the structure of ribonucleic acid (RNA)– Describe the structure and role of messenger RNA
(mRNA)– Describe the structure and role of transfer RNA
(tRNA)
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RNA• RNA = ribonucleic acid• RNA is a single -stranded polymer• Each RNA nucleotide consists of:
– A pentose sugar (ribose)– A phosphate group– A base – adenine, cytosine, guanine,
uracil (instead of thymine)• RNA used in protein synthesis is
messenger RNA (mRNA) or transfer RNA (tRNA).
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RNA contains the pentose sugar ribose.
DNA contains the pentose sugar deoxyribose.
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Messenger RNA (mRNA)
• mRNA is used to transfer the DNA code from the nucleus to the cytoplasm.
• mRNA is complementary to the DNA code.• mRNA is small enough to leave the nuclear pores.• Once in the cytoplasm, mRNA associates with the
ribosomes.• mRNA is used to determine the sequence of amino
acids during protein synthesis.• mRNA is easily broken down and only exists whilst it
is needed to manufacture a protein.• The sequence of nucleotides in the mRNA is
referred to as the genetic code.
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Transcription (forming mRNA)
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The Genetic Code (recap of unit 1)
• 3 nucleotide bases on mRNA (a codon) codes for each amino acid in a protein.
• A few amino acids have a single codon.• The code is degenerate – most amino acids have
more than one codon.• 3 codons code for no amino acids – they are stop
codons and mark the end of the polypeptide chain.• Non-overlapping – each nucleotide is read only
once.• Universal – same codon codes for the same amino
acid in all organisms (few minor exceptions).
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Transfer RNA (tRNA)
• tRNA is a small molecule (~80 nucleotides).• Single stranded and folded into a clover leaf
shape with one end of the chain slightly longer.• This longer section is attached to an amino
acid.• Each tRNA can carry a different amino acid.• 3 bases at the opposite end of the tRNA are
called an anticodon.• Each amino acid has a different anticodon.• The anticodon pairs with the complementary
codon on the mRNA.
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Amino acid joins here
Anticodon
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Comparison of DNA, mRNA and tRNA
Feature DNA mRNA tRNA
Double/Single
Size
Shape
Sugar
Bases
Quantity in cells
Stability
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Comparison of DNA, mRNA and tRNA
Feature DNA mRNA tRNA
Double/Single Double Single Single
Size Largest Variable Smaller
Shape Double helix Single helix Clover shape
Sugar Deoxyribose Ribose Ribose
Bases A, G, T, C A, G, U, C A, G, U, C
Quantity in cells Constant (gametes)
Varies Varies
Stability Very stable Unstable More stable than mRNA, less than DNA
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Polypeptide synthesis – transcription and splicing• Learning Objectives:
– How is pre-mRNA produced from DNA in the process called transcription?
– How is pre-mRNA modified to form mRNA?
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The process by which DNA is ‘read’ to produce a strand of mRNA
A G T C G T C A A T G C T A T G C A T T C C G T A C
T C A G C A G T T A C G A T A C G T A A G G C A T GDNA
mRNAA G U C G U C A A U G C U A U G C A U U C C G U A C
RNA polymeraseCoding Strand
Template Strand
5’
5’
5’
3’
3’
3’
TRANSCRIPTION
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Transcription• Helicase (enzyme) acts on a region
of DNA to break the hydrogen bonds between the bases.
• RNA polymerase moves along one of the two DNA strands – template strand
• RNA polymerase matches up complementary RNA nucleotides.
• C matches G and G matches CU matches A and A matches T
• As the RNA nucleotides join together the pre-mRNA is formed.
• The DNA behind the RNA polymerase rejoins into a double helix.
• When the RNA polymerase reaches a “stop” codon, the chain is terminated and the pre-mRNA detaches.
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Splicing of mRNA to form mRNA
• Once the introns (non-functional DNA) have been removed, the remaining exon sections join together.
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RNA Splicing
snRNPs
Spliceosome
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Fun fact of the day…
• Introns figured prominently in Star Trek: The Next Generation, Season 7, Episode 271, entitled "Genesis."
• In this episode, a synthetic T-cell inadvertently activated the crewmembers' introns, resulting in de-evolution and the expression of ancient physiological traits
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Transcription Animation
http://www.johnkyrk.com/DNAtranscription.html
http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::525::530::/sites/dl/free/0072464631/291136/mRNA_synthesis.swf::mRNA_synthesis.swf
mRNA splicinghttp://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::525::530::/sites/dl/free/0072464631/291136/spliceosomes.swf::spliceosomes.swf
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Polypeptide synthesis – translation
• Learning Objectives:– How is a polypeptide synthesised during the process
of translation?
– What are the roles of mRNA and tRNA in translation?
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A G U C G U C A A U G C U A U G C A U U C C G U A C G
Remember our strand of mRNA from before?
U C A G C A G U U A C G A U A C G U A A G G C A U G C
SER SERALA ALAVAL THR ILE ARG LYS
TRANSLATION
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Synthesising the polypeptide (translation)• mRNA attaches to the ribosome at the “start” codon
– AUG.• tRNA with a complementary anticodon attaches to
the mRNA – UAC.• This tRNA is attached to an amino acid – methionine• The ribosome moves along the mRNA bringing in 2
tRNA molecules at any one time.• An enzyme and ATP are used to join the amino
acids with a peptide bond.• The first tRNA is released and can collect another
amino acid.• The process is repeated until a “stop” codon is
reached.• Many ribosomes can travel along the mRNA at the
same time – polysome.
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Translation Animation
http://www.johnkyrk.com/DNAtranslation.html
http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::525::530::/sites/dl/free/0072464631/291136/protein_synthesis.swf::protein_synthesis.swf
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TASK
Using PCs log ontowww.WolframAlpha.com
Enter sequence of 22 bases from an imaginary DNA coding strand
Try several different strands with same software.
Who can get the most matches to the human genome?
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TASK
Create a model of either TRANSLATION or TRANSCRIPTION
Can be any format e.g.: PowerPoint, Poster, 3D Model