DNA, Replication, Mutations, RNA, & Protein Synthesis
Molecular Genetics
DNA
DNA Notes• Structure
– Watson and Crick (Rosalind Franklin)• Discovered the shape of DNA (p.293)• Double Helix – two strands wound around each
other.
Unravel DNAChromosome
Supercoils
Coils
Nucleosome
Histones
DNAdoublehelix
Red = what you need to know.
DNA Notes• Structure
– Start with a chromosome– Break it down into supercoils– Supercoils are coils piles of nucleosomes.– Nucleosomes are DNA wrapped around
histones.– Histones are proteins used to tightly pack
DNA.– Unravel a nucleosome, you are left with the
histones and the double helix.
DNA StructureDNA consists of two molecules that are
arranged into a ladder-like structure called a Double Helix.
A molecule of DNA is made up of millions of tiny subunits called Nucleotides.
Each nucleotide consists of:1. Phosphate group2. Pentose sugar (Deoxyribose)3. Nitrogenous base
Nucleotides
Phosphate
PentoseSugar
NitrogenousBase
Nucleotides
The phosphate and sugar form the backbone of the DNA molecule, whereas the bases form the “rungs”.
There are four types of nitrogenous bases.
Nucleotides
A
AdenineT
Thymine
G
GuanineC
Cytosine
Double Helix
Hydrogen bonds
Nucleotide
Sugar-phosphate backbone
KeyAdenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
Figure 12-7, page 294
Nucleotides
Each base will only bond with one other specific base.
Adenine (A)Thymine (T)
Cytosine (C)Guanine (G)
Form a base pair.
Form a base pair.
Nitrogenous BasesPurines Pyrimidines
Adenine Guanine
Cytosine Thymine
Phosphate groupDeoxyribose
Backbone
Base
DNA Structure
Because of this complementary base pairing, the order of the bases in one strand determines the order of the bases in the other strand.– Chargaff’s rules
• A pairs (bonds) with T and G bonds with C• So there are the same amount of A’s as there are
T’s.• There is also the same amount of G’s as there are
C’s.
G
G
A
T
T
A
A
C
T
G
C
A
T
C
DNA Structure
A gene is a section of DNA that codes for a protein.
Each unique gene has a unique sequence of bases.
This unique sequence of bases will code for the production of a unique protein.
It is these proteins and combination of proteins that give us a unique phenotype.
Then what is a gene?
GENE
Protein
DNA
Gene
TraitPhenotype: Observable Physical Appearance
DNA REPLICATION
DNA Replication– Before a cell divides, it duplicates its DNA –
this is called replication (Interphase-S phase)
DNA Replication
1. DNA Helicase unzips the original strand at the hydrogen bonds
2. DNA Polymerase brings new nucleotides to bind with the template.
3. DNA Polymerase “proofreads” the bases and repairs any mistakes.
4. Result – two identical strands from one original.
1
2
3
4
What is the function of DNA?*DNA carries the instructions for making the
proteins that determine traits.*Proteins function as:
-antibodies-contractile proteins-transport proteins-storage proteins-enzymes-hormones
DNA…RNA?RNA works with the DNA to make the
protein building instructions...Proteins are made of chains of Amino Acids!!!
Just like DNA is made of strands of nucleotides/base pairs.
More on RNA next time