Concept Map 3

DNA Structure

Double Helix

Made up of Deoxyribose

Attached to the sugars are the four Nitrogenous bases:

Adenine (A)

Connected by chemical bonds

Cytosine (C)

Guanine (G)

Connected by chemical bonds

Thymine (T)

Made up of Phosphate groups

The strands run antiparallel

5' -> 3'

3' -> 5'

Discovered by James Watson and Francis Crick

Enables a cell molecule to copy itself during cell division

DNA Regulation

Eukaryotes

Transcription Factors

General

r

(Basal/background) low levels of transcription

Specific

Activators

r

Increases levels of transcription

Repressors

r

If there is a high level of transcription, reduces levels

10nm fiber

30nm fiber

300nm fiber

Metaphase Chromosome

Nucleosomes

Control Elements

Proximal

r

Bind to general transcription factors

Distal

r

Bind to specific transcription factors (activators/repressors)

Enhancers

Operon

DNA Expression

Gene Activation

Regulatory Elements

Promoter

Enhancers

Silencers

Transcription Factors

Chromatin Modifications

Histone Acetylation

Remodeling

Transcription (DNA --> RNA)

RNA Polymerase

Transcription factors

Elongation

Termination

RNA Splicing

Exons (Expressed)

Introns (Removed)

mRNA Processing

5' cap

Poly A tail

Splicing

DNA Replication

r

Process by which a cell copies its DNA to produce two identical copies

Initiation of DNA Replication

Enzymes separate the two strands

Topoisomerase breaks, swivels and rejoins parental DNA ahead of replication fork

r

Relieves the strain caused by unwinding

Single-strand binding proteins stabilize unwound parental strands

Primase synthesizes RNA primers and uses parental DNA as a template

Helicase unwinds and separates parental DNA strands

Next, there is a formation of a daughter strand or a new polymer of DNA

DNA Polymerases

Add complementary base to daughter strand

Need RNA primer to add nucleotides to

Nucleotides added to 3' end of primer

Polymerization occurs in 5' to 3' direction

Need sliding clamp

Converts DNA pol III from being distributive to processive

Two DNA polymerases needed in bacterial replication

DNA Polymerase I

DNA Polymerase III

Synthesis of Leading Strand

After RNA primer is made, DNA pol III starts to synthesize the leading strand

Leading strand is elongated continuously as the fork progresses

Many Okazaki fragments are made at the lagging strand

DNA pol I removes the RNA primer and replaces it with DNA nucleotides

DNA ligase seals gaps

Models of DNA Replication

Alternate Models of DNA Replication

Dispersive Replication

Each strand of both daughter molecules contains a mixture of old and newly synthesized DNA

Conservative Replication

Two parental strands reassociate after functioning as templates for new strands

Restore the parental double helix

Operon

lac Operon

Operator

Negative Regulation

Repressor bound

No transcription

No repressor

Positive Regulation

Activator bound

Transcription

No Activator

Promoter

Lac L: Regulatory Gene

Operon On

Lactose present

Lactose Present, no glucose

Operon Off

Glucose present

Glucose and lactose present

Nothing Present

Structural genes

Lac Z: B-galactoisdase

Lac A: Trans-acetylase

Lac Y: Permease

Histones

H1

r

links histones together to form the nucleosome

H2A

Histone Core (Octamer)

H2B

H3

H4

Semiconservative replication

r

Two strands of the parental molecule separate and function as a template for synthesis of a new, complementary strand

Parental molecule has two complementary strands of DNA

Each base is paired by hydrogen bonding with its specific partner

Two DNA strands are separated

r

Each parental strand serves as a template for a new complementary strand.

Nucleotides complementary to the parental strand are connected

r

Form the sugar-phosphate backbones of the new daughter strands