Exam 3 Study Guide

mutations

heritable changes in DNA; drive evolution and change; can be positive, negative, neutral

single-cell organism mutations

ALL daughter cells have the mutation

multicellular organism mutations

mutations can be either somatic or germ-line

somatic (non-sex) cells

passed to daughter cells in area, is localized

germ-line (sex) cells

passed to new organism

gene⁺

wildtype version of gene

gene^-

mutated version of gene

sources of mutations

uncorrected mistakes in replication, chemical mutagens, high-intensity radiation

uncorrected mistakes in replication

accounts for the most mutations

chemical mutagens

DNA is exposed to to chemicals which alter the structure of the bases

frequency of mutations in e.coli

4 mutations per 100 cell divisions

frequency of mutations in humans

1 mistake per 1 billion nucleotides

frequency of mutations of e.coli in vitro

DNA polymerases make 400 mistakes per cell division

proofreading

DNA polymerase’s “backspace key” that has the ability to check the last base added and if it’s wrong, cut it out and try again; uses 3’ to 5’ exonuclease activity

MMR

methyl-directed mismatch repair

methyl-directed mismatch repair system

identifies if there’s a problem to fix and if you can tell difference between parental strand and daughter strand; looks for GATC 5’ to 3’ and check if there’s a methyl on A

hemimethylated DNA

when one strand has a methyl on Adenine and the other doesn’t; can help us to tell the difference from parent template to daughter strand

DNA replication

most reliable, has proofreading and repair mechanisms; mistakes lead to alterations in the nucleotide sequence in DNA (mutations) and passed to daughter cells during cell division

mismatch repair system

identifies if there’s a problem to fix and corrects mismatched bases with mismatch repair enzymes in the unmethylated (new) strand; DNA Polymerase III fills the gap, ligase seals the nick

fully methylated DNA

both strands have methyl on adenine

mutS

scans DNA looking for a problem in the DNA in general because it can’t distinguish hemi-methylated from fully-methylated DNA

mutH

scans DNA looking for hemi-methylated GATC DNA sequences; can acts as endonuclease to cut somewhere on the newly synthesized non-methylated strand

mutL

links mutS and mutH so they are aware of each other by folding DNA over

during skeletal muscle contraction, what changes?

length of sarcomere, length of region occupied only by actin (I-Band shrinks), and length of region occupied only by myosin (H-zone shrinks)

mutation types

point mutations and chromosomal-level mutations

point mutations

localized to 1-4 nucleotides (base substitution and frameshift)

chromosomal-level mutations

mutation on a bigger, chromosomal level that affects thousands of base pairs (insertions, deletions, translocation, inversion, duplication)

base-substitution mutations

(point mutation) replace on base pair with another; callled same-sense, missense, or nonsense

base substitution mutation transition

changes a purine to a purine, or a pyrimidine to a pyrimidine (C to T) (G to A)

base substitution mutation transversion

change the nitrogenous base family (purine to pyrimidine)(C to G)

3 categories of base substitutions

missense, nonsense, same-sense (silent)

missense mutation

substitute one amino acid-specifying codon for a different one (changes the amino acid); protein effect varies

nonsense mutation

substitute a codon for a stop codon (Leu to UAG STOP codon) and causes premature termination; protein can be truncated and become inactive

same sense (silent) mutation

substitution results in the coding of the same amino acid due to redundancy/degeneracy; no effect on protein product/function

missense mutation protein effect

if what you changed was important to protein function or the amino acid you replaced performs the same function, then the protein can be fully functional and retain some function

BUT if the altered amino acid is critical and the new amino acid doesn’t make up for it, then the protein will be nonfunctional

missense amino acid changes

positive charge to positive charge amino acid = good

negative charge to hydrophobic amino acid

soluble

means you are nit stuck to a membrance

membrane-bound

protein stuck to a membrane

sickle cell anemia

heterotetramer (2 alpha, 2 beta); defective Beta-globin subunit in hemoglobin protein; caused by a single base pair substitution that changes charge of protein