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