Unit 2 - 7. DNA Structure & Replication Flashcards
1
Q
Properties of DNA that make it the Ideal Genetic Material
A
- Storage of Genetic Information
- Replication
- Expression of Genetic Information
- Mutability
2
Q
Frederick Griffith (1928)
A
- injected pneumococci bacteria into mice
- observed transformation
- heredity information in the heat-killed pathogenic strain was transferred to live, nonpathogenic strain, transforming the nonpathogenic strain into pathogenic cells which caused the mice to die
3
Q
Avery, McLead, and McCarty (1944)
A
- identified the transforming substance as DNA
- used protease and DNase in an experiment with mice
4
Q
Hershey and Chase (1952)
A
- provided more conclusive evidence that DNA was the genetic material
- ran experiments on bacteriophages (a virus that infects bacteria and transfers genetic information to them, they consist of DNA surrounded by a protein coat)
5
Q
Watson and Crick (1955)
A
- discovered DNA structure
- based their model on available information from previous studies
6
Q
Previous Studies Watson and Crick used:
A
- X-rays of pure DNA crystals (Maurice Wilkins, Linus Pauling, Rosalind Franklin)
- Data from Chargoff on chemical composition of DNA: A=T; C=G
7
Q
Major features of Watson and Crick model
A
- DNA is composed of two anti-parallel nucleotide chains
- the 2 chains are coiled around a central axis to form a helix
- bases on interior of helix w. sugar-phosphate backbone on exterior
- the 2 chains are held together by hydrogen bonds between complementary bases in opposite chains
- the sequences of bases along the 2 strands are complementary - i.e. the sequence of bases on the 2nd strand is determined by the 1st strand
8
Q
Meselson and Stahl (1958)
A
- found evidence to support semi-conductive method
- Grew E.Coli in Nitrogen 15 medium, then placed them in Nitrogen 14
- The DNA was sequenced buy equilibrium centrifugation in a density gradient
9
Q
Nucleoside vs. Nucleotide
A
Nucleoside = nitrogenous base + sugar Nucleotide = nitrogenous base + sugar + phosphate
10
Q
DNA vs. RNA
A
DNA:
- double stranded
- A=T, G=C
- found/synthesized in the Nucleus
- storage of genetic information in majority of living organisms
RNA:
- single stranded
- A =U, G=C
- found/synthesized in Ribosome/cytoplasm
- stores genetic information for certain viruses
- transfers genetic info from nucleus to cytoplasm where proteins are made
11
Q
Purines
A
- 2 rings
- Adenine & Guanine
12
Q
Pyrimidine
A
- 1 ring
- Cytosine, Thymine, and Uracil
13
Q
Unique/Single Copy DNA
A
- DNA whose nucleotide sequences is represented only once in the haploid genome
- occurs in very long stretches
- comprises 50-60% of total DNA
14
Q
Moderately Repetitive DNA
A
- sequence repeated 100-1000 times in genome
- constitutes 25-40% of genome
- contains genes coding for rRNA and histones
- some can be “junk” DNA (no function)
15
Q
Highly repetitive DNA
A
- short sequences (5-10 bp) repeated thousands/millions of times in the genome
- 10-15% on human DNA
- highly localized in specific sites of the chromosomes (centromeres, telomers)
16
Q
Semi-conservative
A
- DNA replicates by separation of the two strands
- each functioning as template for new strand (complimentary)
17
Q
DNA Synthesis Requires
A
- DNA
- dATP, dGTP, dTTP, dCTP (deoxynucleotide triphosphates
- DNA polymerase enzymes + additional enzymes (helicase, ss binding protein, primase, exonuclease, ligase)
- Primer
18
Q
Steps in DNA Replication
A
- Initiation
- Elongation
- Termination
19
Q
Initiation
A
- starts at replication fork / origin of replication
- DNA helicase unwinds by breaking hydrogen bonds
- single-stranded binding protein keeps strands apart
20
Q
Elongation
A
- RNA primase lays down RNA primer
- DNA polymerase recognizes primer and adds dNTPs (Reads 3’-5’; Builds 5’-3’)
- lagging strand, leading strand, okazaki fragments
- DNA polymerase proof reads
- Exonuclease removes mismatched bases
21
Q
Termination
A
- synthesis ends when DNA polymerase reaches end of strand
- DNA ligase connects last Okazaki fragments
