Exam 3- Ch. 14

electrophoresis

electrophoresis

technique used to separate DNA fragments according to size

helicase

during replication, this enzyme helps to open up the DNA helix by breaking the hydrogen bonds

induced mutation

mutation that results from exposer to chemical or environmental agents

lagging strand

during replication, the strand that is replicated in short fragments and away from the replication fork

leading strand

strand that is synthesized continuously in the 5'-3' direction, which is synthesized in the direction of the replication fork

ligase

enzyme that catalyzes the formation of a phosphodiester linkage between the 3' OH and 5' phosphate ends of the DNA

mismatch repair

type of repair mechanism in which mismatched bases are removed after replication

mutation

variation in the nucleotide sequence of a genome

nucleotide excision repair

type of DNA repair mechanism in which the wrong base, along with a few nucleotides upstream or downstream, are removed

Okazaki fragment

DNA fragment that is synthesized in short stretches on the lagging strand

point mutation

mutation that affects a single base

primase

enzyme that synthesizes the RNA primer; the primer is needed for DNA pol to start synthesis of a new DNA strand

primer

short stretch of nucleotides that is required to initiate replication; in the case of replication, the primer has RNA nucleotides

proofreading

function of DNA pol in which it reads the newly added base before adding the next one

replication fork

Y-shaped structure formed during initiation of replication

silent mutation

mutation that is not expressed

single-strand binding protein

during replication, protein that binds to the single-stranded DNA; this helps in keeping the two strands of DNA apart so that they may serve as templates

sliding clamp

ring-shaped protein that holds the DNA pol on the DNA strand

spontaneous mutation

mutation that takes place in the cells as a result of chemical reactions taking place naturally without exposure to any external agent

telomerase

enzyme that contains a catalytic part and an inbuilt RNA template; it functions to maintain telomeres at chromosome ends

telomere

DNA at the end of linear chromosomes

topoisomerase

enzyme that causes underwinding or overwinding of DNA when DNA replication is taking place

transformation

process in which external DNA is taken up by a cell

transition substitution

when a purine is replaced with a purine or a pyrimidine is replaced with another pyrimidine

transversion substitution

when a purine is replaced by a pyrimidine or a pyrimidine is replaced by a purine

Frederick Griffith

Found something is carried in bacteria to kill the mouse, DNA is not understood to be genetic yet, mouse with R and S cells, first transformation in bacteria

Alfred Hershey and Martha Chase

DNA is the substance of inheritance, experiment with protein entering e-coli cell, 1950s

Erwin Chargaff

1950s, DNA varies with species and amount of A=T vs G=C, “Chargaff’s Rule”

Rosalind Franklin and Maurice Wilkins

Used X-Ray crystallography to find molecular structure of DNA

James Watson, Francis Crick and Maclyn McCarty

Found the X-Ray diffraction pattern of DNA, elucidating its double helix structure

What is the structure of double-stranded DNA?

helical structure, double bond polymer with repeating nucleotides bound covalently by phosphodiester bonds, 2 anti-parallel sugar-phosphate backbones with nitrogenous bases paired (A::T and G:::C) held together by hydrogen bonds

Why and how does replication of the lagging strand differ from the replication of the leading strand?

the lagging strand replicates discontinuously forming short fragments, whereas the leading strand replicates continuously

What is the end replication problem and how do eukaryotic cells solve this problem?

Telomere makes sure the DNA replicates all the way to the end, adds extra track to fill in gaps before it is deleted again

What are the three different methods that cells use to minimize mutations in their genome?

DNA polymerase proofreads newly made DNA during replication

Mismatch Repair replaces an incorrect base after replication using nuclease

Nucleotide Excision Repair is repair of damaged from excess UV light or chemicals, repairs thymine dimers with a cut and paste method

How do DNA histones from nucleosomes?

The nucleosome is composed of a core of histone proteins around which the DNA double helix is wrapped

How is chromatin organized into higher-order structures?

1. 10-nm = Histones + DNA

2. 30-nm = Nucleosomes

3. 300-nm = Chromatin Loops

4. 700-nm - Chromatin

5. 1400-nm = Chromosome

What is the difference between euchromatin and heterochromatin?

euchromatin is loosely expressed DNA that gets expressed, while heterochromatin is DNA that does not get expressed

Friedrich Miescher

1869, isolated phosphate rich acidic compounds from nuclei of pus (now called DNA)

Phoebus Levene

1920s, isolated sugars in DNA and RNA finding C, G, A, and T