Chapter 16 DNA and Inheritance Flashcards
TH Morgan
- Studied the X chromosome of male fruit flies with white eyes
- Found that genes are on chromosomes
- 1910
Frederick Griffith
- Cultured harmless rough bacteria with heat-killing pathogenic bacteria resulting in dead mice
- Found that the transforming principle is a change in materialized trait
- 1928
Avery, McCarty, MacLeod
- Injected only protein or only DNA from pathogenic bacteria into mice
- Found that transforming principle is a result of DNA, not proteins
- 1944
Erwin Chargaff
- Analyzed molecular contents of DNA
- Found that DNA varies from species to species and [A]=[T] and [C]=[G]
- 1950
Hershey and Chase
- Grew phage viruses with radioactive sulfur or phosphorus, infected bacteria, blended, and centrifuged
- Found that the DNA of the virus, not the proteins, infected the bacteria
- 1952
Watson and Crick
- Used Chargaff’s rules, Pauling’s alpha helical structure of proteins, and Franklin’s X-ray crystallography
- Developed the double helix model of DNA
- 1953
Rosalind Franklin
- Produced X-ray crystallography images of DNA, with a clear double helix pattern
- Discovered the sugar-phosphate backbone lies on the outside of the helix molecule
- 1953
Meselson and Stahl
- Cultured bacteria in heavy nitrogen (15N), then in a lighter isotope (14N) and sampled after generation 1 and 2
- Found that DNA replication follows the semi-conservative model
- 1958
What is transformation?
Transformation- a change in genotype and phenotype due to assimilation of foreign DNA
What are bacteriophages?
viruses that infect bacteria
What are the components of bacteriophages?
phage head, tail sheath, tail fiber, and DNA
What are Chargaff’s rules?
- The base composition of DNA varies between species
- In any species the number of A and T bases are equal and the number of G and C bases are equal
What are the two components of DNA?
The two components of DNA are the sugar phosphate backbone and the nitrogenous bases
What molecules are at the 3’ and 5’ ends?
Phosphate hanging off of the 3’ end and deoxyribose hanging off of the 5’ end
What is the structure of DNA?
Double helix
What are the bonds between bases?
Hydrogen bonds
The backbones of DNA are _________
antiparallel
What are the two types of bases?
Purine and pyrimidine
How many rings does a purine have? Pyrimidine?
- Purine- 5 and 6
- Pyrimidine- 6
How many bonds are there between the bases?
- G: .C
- A:T
What is the semi-conservative model?
when a double helix replicates, each daughter molecule will have one old strand (derived or “conserved” from the parent molecule) and one newly made strand
What were incorrectly proposed models for DNA replication?
Competing models were the conservative model (the two parent strands rejoin) and the dispersive model (each strand is a mix of old and new)
Where does replication begin? And what does it form there?
Replication begins at particular sites called origins of replication, where the two DNA strands are separated, opening up a replication “bubble”
How many origins or replication does a prokaryotic cell have? Eukaryotic?
Prokaryotic- one
Eukaryotic- hundreds or thousands
What is a replication fork?
- a Y shaped region where new DNA strands are elongating
- located at the end of each replication bubble
What do helicases do?
untwist the double helix at the replication forks
What do single strand binding proteins do?
bind to and stabilize single stranded DNA
What does topoisomerase do?
corrects overwinding ahead or replication forks by breaking, swiveling, and rejoining DNA strands
What do DNA polymerases do?
catalyze the elongation of DNA at a replication fork
What do most DNA polymerases require?
a primer and a DNA template strand
What is the rate of elongation of DNA in bacteria and human cells?
The rate of elongation is about 500 nucleotides per second in bacteria and 50 per second in human cells
What can’t DNA polymerases do?
DNA polymerases cannot initiate synthesis of a polynucleotide; they can only add nucleotides to the 3’ end
What is the initial nucleotide strand?
a short RNA primer
What enemy forms the primer, and what can it do?
Primase can start an RNA chain from scratch and adds RNA nucleotides one at a time using the parental DNA as a template
Describe each nucleotide added to a DNA strand?
Each nucleotide that is added to a growing DNA strand is a nucleoside (sugar and a base) triphosphate
How does DNA gain energy to replicate?
- dATP supplies adenine to DNA and is similar to the ATP of energy metabolism
- As each monomer of dATP joins the DNA strand, it loses two phosphate groups as a molecule of pyrophosphate
What aspect of DNA structure affects replication?
antiparallel
How does the antiparallel structure of DNA affect replication?
DNA polymerases add nucleotides only to the free 3’ end of a growing strand; therefore, a new DNA strand can elongate only in the 5’ to 3’ direction
How is the leading strand synthesized?
Along one template strand of DNA, the DNA polymerase synthesizes a leading strand continuously, moving toward the replication fork
How is the lagging strand synthesized?
DNA polymerase must work in the direction away fro the replication fork.
What are the fragments formed by the lagging strand called and what binds them?
The lagging strand is synthesized as a series of segments called Okazaki fragments, which are joined together by DNA ligase
What is the model for how DNA polymerase makes new DNA molecules?
DNA polymerase molecules “reel in” parental DNA and “extrude” newly made daughter DNA molecules
What is the function of DNA pol 1?
DNA Pol 1- Removes RNA molecules of primer from 5’ end and replaces them with DNA nucleotides
What is the function of DNA pol 3?
DNA Pol III- Using parental DNA as a template, synthesizes new DNA strand by covalently adding nucleotides to the 3’ end of a pre-existing DNA strand or RNA primer
Describe an alternative function for DNA polymerase.
DNA polymerases proofread newly made DNA, replacing any incorrect nucleotides
How may DNA be damaged?
DNA can be damaged by exposure to harmful chemical or physical agents such as cigarette smoke and X-rays; it can also undergo spontaneous changes
What is nucleotide excision repair?
a nuclease cuts out and replaces damaged stretches of DNA
What is the name for the proofreading mechanism in which a nuclease cuts out and replaces damaged stretches of DNA?
nucleotide excision repair
How does altered DNA impact evolution?
- Error rate after proofreading repair is low but not zero
- Sequence changes may become permanent and can be passed on to the next generation
- These changes (mutations) are the source of the genetic variation upon which natural selection operates
What are telomeres?
special nucleotide sequences at the end of eukaryotic chromosomal DNA molecules
What do telomeres do?
postpone the erosion of genes near the ends of DNA molecules
What is the shortening of telomeres connected to?
aging
What is the function of telomerase?
catalyzes the lengthening of telomeres in germ cells
What does a chromosome consist of?
a DNA molecule packed together with proteins
Describe the structure of a bacterial chromosome?
The bacterial chromosome is a double-stranded, circular DNA molecule associated with a small amount of protein
Describe the structure of a eukaryotic chromosome.
Eukaryotic chromosomes have linear DNA molecules associated with a large amount of protein
Where is DNA located in a bacterium?
In a bacterium, the DNA is “supercoiled” and found in a region of the cell called the nucleoid
What is chromatin?
a complex of DNA and protein, is found in the nucleus of eukaryotic cells
How do chromosome fit into the nucleus?
through an elaborate, multilevel system of packing
What is loosely packed chromatin called?
euchromatin
What is highly condensed chromatin called and what are some examples?
heterochromatin
centromeres and telomeres
What makes heterochromatin significant?
Dense packing of the heterochromatin makes it difficult for the cell to express genetic information coded in these regions
