lecture 4 cell biology
TRANSCRIPT
-
8/8/2019 Lecture 4 Cell Biology
1/22
-
8/8/2019 Lecture 4 Cell Biology
2/22
NUCLEIC ACIDS1-They are the most important macromolecules in the cells
of all living organisms2- They are carriers of genetic information
3-There have Two forms (RNA and DNA)
Composition and structure of nucleic acids Nucleic acid molecule is a polymers of monomeric unit
called nucleotides . These nucleotide monomer unitare joined by the formation of phosphodiester bond
-
8/8/2019 Lecture 4 Cell Biology
3/22
Nucleotide Nucleotides composed of:
(1) P entose (C5) sugar , either ribose (RNA) or deoxyribose (DNA)
Five-carbon pentose in DNA called 2-deoxyribose where the OHgroup on the 2 prime (2) carbon of ribose is replaced with H atom
but not in RNA.
-
8/8/2019 Lecture 4 Cell Biology
4/22
Nucleotide( 2)Nitrogen bases which belong to two chemical classes- Purine bases (adenine and guanine): contain two fusedheterocyclic rings
- Py rimidine bases (thymine, cytosine, and uracil): containa single six-memb
ered heterocyclic ring
(3) Phosphate group
-
8/8/2019 Lecture 4 Cell Biology
5/22
B ondPhosphodiester - Phosphate linkage that connects two sugars by
ester linkage- Diester bond is one which involves two ester
bond
- Phosphodiester bond will be formed between anytwo adjacent nucleotides (5 phosphate of onenucleotide and the 3 hydroxyl of another)
-
8/8/2019 Lecture 4 Cell Biology
6/22
Nucleotide
Nucleoside : nitrogen base bonded to its C 5 sugar Nucleotide : nitrogen base attached to C 5 sugar byglycosidic linkage and bonded to a phosphate
-
8/8/2019 Lecture 4 Cell Biology
7/22
NucleotideF
unction: M ajor components of nucleic acids Key forms of chemical energy (e .g. , ATP) Carriers of sugars in biosynthesis of polysaccharides
Regulatory molecules for certain enzymes or metabolic events
-
8/8/2019 Lecture 4 Cell Biology
8/22
Nucleotide
PO 4
Nucleoside
O-
P O
O-
O-
Ribose
Nitrogen base
PentoseSugar
Deoxyribose
Purines
DNA
RNA
(A)
(G)Pyrimidines
(T)
(U)
(C)
-
8/8/2019 Lecture 4 Cell Biology
9/22
Primar y Structure of nucleic acidIs a Sequence of nucleotides in a DNA or RNA molecule- oligonucleotide : small polymer contains only a few
nucleotides- pol ynucleotide : very large polymer contains thousand or
millions of nucleotides- the polynucleotide chain (strand) has a sense of directionwith one end of the chain terminating in a 5 phosphategroup and the other in a 3 hydroxyl group of growing
Chain- the sequence of bases in RNA and DNA is written in the5 to 3 direction
-
8/8/2019 Lecture 4 Cell Biology
10/22
Two polynucleotide strands wrap around eachother to form a DNA double helixThe two strands are associated because particular
bases always hydrogen bond to one another A pairs with T , and C pairs with G , producing basepairs
Base pairing of nitrogen bases
-
8/8/2019 Lecture 4 Cell Biology
11/22
Types of nucleic acid1- DNADouble-stranded molecules consisting of twocomplementary polynucleotide chains running in oppositedirectionStrands held together by hydrogen bonds
Basepair
-
8/8/2019 Lecture 4 Cell Biology
12/22
Types of nucleic acid2- RNARNA is usually a single polynucleotide strandDemonstrates secondary structure (folding back upon itself)
Four classes: mRNAs, tRNAs, rRNAs, and small RNAs
-
8/8/2019 Lecture 4 Cell Biology
13/22
-
8/8/2019 Lecture 4 Cell Biology
14/22
W hat is the Gene?A particular nucleotide sequencethat can instruct the formation of a
polypeptide is called a geneM ost DNA molecules consist of
millions of base pairs and,consequently, many genesHuman genome contain about 3
billion nucleotides and 30000genesThese genes, many of which areunique to the species, determinethe structure of proteins and, thus,lifes structures and functions
-
8/8/2019 Lecture 4 Cell Biology
15/22
W hat is the Gene?
-
8/8/2019 Lecture 4 Cell Biology
16/22
Enzymes
-
8/8/2019 Lecture 4 Cell Biology
17/22
EnzymesE
nzymes are specialized macromolecules that speed upchemical reactions in cellsProperties:1- They are Catalytic proteins( biological catalysts) that
accelerate the rate of biological2- enzymes can be denatured and precipitated with salts,
solvents and other reagents .3- M any enzymes require the presence of other compounds -
cofactors - before their catalytic activity can be exerted .
4- I ncrease the rate of chemical reaction without themselves being consuming or permanently altered by the reaction
5- I ncrease reaction rates without altering the chemicalequilibrium between reactants and products
-
8/8/2019 Lecture 4 Cell Biology
18/22
Enzymes6 - E nzymes are usually very specific as to which reactionsthey catalyze and the substrates that are involved in
these reactions .
-
8/8/2019 Lecture 4 Cell Biology
19/22
CofactorsC ofactors and coenz ymesSome enzymes do not need any additional componentsOthers require non-protein molecules called cofactors to be
bound for activity
C ofactors can be:- inorganic (e.g. , metal ions and iron-sulfur clusters)- organic compounds (e .g. , flavin and heme) . which can
be either:
- prosthetic groups , which are tightly bound to anenzyme and play critical function roles (e .g : heme, Zinc)- coenz ymes, which are released from the enzyme's
active site during the reaction, they called coenzymes
because they work together with enzymes.
-
8/8/2019 Lecture 4 Cell Biology
20/22
E nzyme classificationE C 1 Oxidoreductases : catalyze oxidation/reductionreactionsE C 2 T ransferases : transfer a functional group (e .g . amethyl or phosphate group)E C 3 H ydrolases : catalyze the hydrolysis of various
bondsE C 4 L yases : cleave various bonds by means other thanhydrolysis and oxidationE
C 5 Isomerases : catalyze isomerisation changes withina single moleculeE C 6 Ligases : join two molecules with covalent bonds
-
8/8/2019 Lecture 4 Cell Biology
21/22
Factors influencing enzyme functionpH: E nzymes in your stomach may prefer an acidicenvironment with a low pH while enzymes elsewhere maynot .
higher temperatures speed reactions -- to a point . Above
104 degrees Fahrenheit, enzymes become denatured andcan no longer catalyze reactions .
Higher concentrations of substrate also speed reactionsuntil the solution reaches a saturation point .Past that
point, the addition of substrate will not affect the velocity of the reaction .
Irreversible inhibition occurs when the inhibitor addeddenatures or destroys the enzyme .
-
8/8/2019 Lecture 4 Cell Biology
22/22
Structure of Cell Membrane Good Luck
Dr Mona