AP Biology Chapter 16 Study Guide

DNA

Directs the development of biochemical, anatomical, physiological, and behavioral traits

-Copied in DNA replication

-Cells can repair DNA

-Didn't know DNA held the genetic information, knew it was made up of chromosomes and is passed down from parents

Frederick Griffith

-1928

-Discovered Transformation

-Mixed heat-killed pathogenic S-strain with living R-strain cells -> Turned living R into living S -> Killed the mice

-S Cells were pathogenic and mice died

-R cells were nonpathogenic and mice lived

Avery, McCarty, and MacLeod

-1944

-Found transforming agent to be DNA

-16 years after Griffith

Phages (Bacteriophages)

-Inject DNA into host cells

-used in molecular genetics research

-A virus is DNA (sometimes RNA) enclosed by a protective coat, often simply protein

Chargaff

-1950

-DNA composition varies, DNA is diverse

-Chargaff's rules:

a) Base composition of DNA varies between species

b) In any species the number of A and T bases are equal and the number of G and C bases are equal

Hershey & Chase

-1952

-Found DNA as the genetic material of phage T2

-Studied E. coli

-DNA has phosphorus (found in pellet)

-Proteins have sulfur (found in liquid)

Wilkins & Franklin

-1953

-Used X-ray crystallography

-Franklin produced a DNA molecule picture

-Found the Double Helix Shape

-Found the width of the helix (2 nm) and the spacing of the nitrogenous bases (.34 nm, 10 in one turn, 3.4 nm in one turn)

Nucleotide

-Phosphate Group

-Pentose Sugar

-Nitrogenous Base (A, T, C, G)

AT (2 Hydrogen bonds) CG (3 hydrogen bonds)

Watson & Crick

-1953

-Created the double helix model of DNA

-Found the 2 outer sugar-phosphate backbones

-Nitrogenous bases paired in the molecule's interior

-Antiparrallel

-Explains Chargaff's Rules: A=T, C=G

Meselson & Stahl

-Used N-15 & N-14, radioactive isotopes

-Found DNA to be semi-conservative

-After Watson & Crick

-Ruled out the other options (Dispersive or Conservative)

DNA Replication

-Semiconservative Model (Meselson & Stahl)

-Remarkable in its speed and accuracy

-More than 12 enzymes and proteins participate in it

-DNA elongates in the 5' to 3' direction, can only add to 3' end

-Adds 50 Nucleotides per second

Bacterial DNA Replication

-Circular DNA

-Creates another circle

-One replication bubble

Eukaryotic DNA Replication

-Multiple origins of replication

-Parental strands of DNA are unwinding

Origins of Replication

Site where 2 DNA strands are separated, opening up a replication "bubble"

-Eukaryotic chromosome may have hundreds or thousands of these

Replication Bubble

Site where DNA replication occurs

Replication Fork

Y-shaped region where new DNA strands are elongating

Helicase

Enzyme that untwists the double helix at the replication forks

Single-strand binding proteins

Bind to and stabilize single-stranded DNA

Topoisomerase

Corrects "overwinding" ahead of replication forks by breaking, swiveling, and rejoining DNA strands

Primase

Lays down the primer

RNA Primer

Allows DNA to be replicated

• 5-10 nucleotides long

DNA Polymerase III

Adds new nucleotides

-Adds to the free 3' end of a growing strand

DNA Polymerase I

Removes RNA nucleotides of primer from 5' end and replaces them with DNA nucleotides

Leading Strand

Synthesized continuously, moves towards the replication fork

-5' to 3'

Steps:

1) Primer

2) DNA Pol III

Lagging Strand

-Goes away from the replication fork

-Made up of Okazaki fragments

-Made backwards to meet antiparralel rule

Steps:

1) Helicase

2) Single-strand binding proteins

3) Primase -> Primer

4) DNA Pol III adds nucleotides 5' to 3', adding to 3' end

5) DNA Pol I removes primer

6) DNA Ligase joins okazaki fragments

DNA Ligase

Joins together Okazaki fragments of lagging strands

-Joins 3' end of DNA that replaces primer to rest of leading strands

3'

Can add nucleotides

-Contains the pentose sugar

5'

Contains the phosphate group

Mismatch Repair

Repair enzymes correct errors in base pairing

Nucleotide excision repair

A nuclease cuts out and replaces damaged stretches of DNA

Telomeres

Special nucleotide sequences at the end of Eukaryotic chromosomal DNA