Chapter 10 and 11 DNA and chromosomal Structure

Genetic Material must contain

• Contain complex information

• Replicate faithfully

• Encode the phenotype

  • have capacity to vary

How to tell that DNA is genetic material

• DNA is organized into chromosomes

• RNA and proteins are everywhere

• Amount of DNA and # of chromosomes correlate

• Diploid has twice as much DNA as haploid

Frederick Griffith Study

studied transformation in bacteria Streptococcus pneumoniae

• studied 2 strains

• S: virulent, smooth and encapsulated

• R: avirulent, rough and non-encapsulate

Hershey-Chase Experiment

Provided additional support for DNA as genetic material (transforming principle)

• E coli. bacteria

  • Bacteriophage T2
    Differential labeling of proteins vs. DNA

What are Nucleic Acids composed of

Composed of Nucleotides

• Phosphate group

• five-carbon sugar (pentose)

  • cyclic nitrogen-containing compound called base

Purines

Type of nitrogenous base
Two ring structure, larger than pyrimidines

Key Purines

Adenine (A) -found both in DNA and RNA and pairs with thymine or uracil via hydrogen bonds
Guanine (G) - found in both DNA and RNA pairs with cytosine

Pyrimidines

nitrogenous bases complementary to purines and are single ring structure (smaller than purines)

Types of pyrimidines

Cytosine - found in DNA and RNA
Thymine - Only found in DNA
Uracil - only found in RNA and replaces (thymine)

Methylation

can affect expression of genes turning them off or on

Deoxyribonucleotides

building blocks of DNA
dATP, dGTP, dCTP, dTTP
d stands for deoxy
TP stands for triphosphate

deoxy

means sugar lacking an oxygen on the 2’ carbon

Triphosphate

has 3 phosphate groups which store energy

Secondary structure of DNA

Two strands form a double helix
Sugar phosphate backbone formed via phosphodiester bonds
hydrogen bonds connect bases
Are antiparallel and complementary

RNA structure

Nucleotides are connected with phosphodiester linkages
Single stranded
Uracil replaces thymine
Ribose sugar has a 2’ OH

ribose (RNA sugar) vs deoxyribose (DNA sugar)

ribose has a hydroxyl group (-OH) on the 2’ carbon
Deoxyribose just has a hydrogen (-H) on the 2’ carbon

• Deoxy - without oxygen

Chargaff’s Rules: Evidence for Double Helix

Determined that adenine = thymine and guanine = cytosine

• A+G =C+T

• purine = pyrimidine

• only for double stranded DNA

How far are bases approximately apart from each other in DNA

.34 nanometers

Structure of DNA double Helix

Right handed helix (twists clockwise as it moves away from you)

Sugar phosphate backbone

Bases held together by hydrogen bonding

10 base pairs per turn

.34 nm apart

2nm diameter to helix

B form of helix

possible helix structures

B-DNA
A-DNA
Z-DNA

B-DNA

Physiological DNA
most common
Right handed
10 nucleotides/turn

1.9 nm wide

A-DNA

high salt or partially dehydrated
Condensed, trades wide for length

Right handed

11 nucleotide per turn
2.3 nm wide

Z-DNA

GCGCGCG repeating oligos
Roles in expression and tension reduction. Not fully understood

Left handed
12 nucleotides per turn
1.8 nm wide

Major groove

Larger space between the backbones of DNA
Proteins that regulate transcription often bind in the major groove because its wider and exposes more chemical information from the bases

Minor groove

smaller space between the backbones of DNA, therefore more restricted

Hairpin structures

In single strands of nucleic acids since self-complementary pairs of the strand can base-pair with another part of the same strand to from “double stranded stem” and the unpaired nucleotides between them make the loop at the end
looks like a stem-and-loop

H-DNA

triple stranded (triplex) DNA; formed when DNA unwinds and one strand pairs with double stranded DNA from another part of the molecule

• Often occurs in lond sequences of only purines or only pyrimidines
  - purines strand paired with 2 pyrimidine strands
  -pyrimidine strand paired with 2 purine stands

• common in mammalian genomes

mammalian genomes

complete sets of genetic material