Mutations

0.0(0)
studied byStudied by 0 people
learnLearn
examPractice Test
spaced repetitionSpaced Repetition
heart puzzleMatch
flashcardsFlashcards
Card Sorting

1/31

flashcard set

Earn XP

Description and Tags

Exam 3

Study Analytics
Name
Mastery
Learn
Test
Matching
Spaced

No study sessions yet.

32 Terms

1
New cards

What processes depend on nucleotide base pairing?

DNA Replication
Transcription
Translation

none are perfect

2
New cards

What type of DNA base pairing in the most reliable? Why?

DNA replication

It needs to be the most reliable mistakes in DNA alter the blueprint, which can affect all subsequent processes and are passed to daughter cells. You can always make a new transcript or protein, but you can’t make a new blueprint.

3
New cards

Define Mutations

Her

4
New cards

How do mutations differ in single-celled organisms vs. multi-cell organisms?

single-cell: all daughter cells have the mutation

multi-cell: mutations can be somatic (threat to individual, not species) or germ line/somatic (threat to individual and species)

5
New cards

What factors can cause changes in DNA sequences?

  • uncorrected mistakes in replication

  • chemical mutagens

  • high-intensity radiation (ex. x-rays, UV, etc.)biological agents (ex. viruses, transposons)

6
New cards

What factor accounts for the most mutations? Why?

DNA replication

Happens so frequently that there’s more possibility for error

7
New cards

How often do errors occur in DNA replication of E. coli? (mutations/cell division), (mutations/nucleotide)

0.04 mutations per cell division

1 mistake per billion nucleotides

8
New cards

How does E. coli reduce DNA replication errors by 104

Proofreading and Methyl-directed Mismatch Repair (MMR)

9
New cards

Steps for proofreading

  1. DNA polymerase inserts incorrect base

  2. Base moves to exonuclease site of DNA polymerase and is cleaved off (3’—5’ exonuclease activity)

  3. DNA polymerase inserts correct base

molecular backspace key

reduces errors 100-fold

10
New cards

Steps for mismatch repair system (MMR)

The MMR corrects mistakes in the newly synthesize (unmethylated) strand missed during proofreading

once DNA gets method, no way to distinguish parent from daughter strand

  1. MutS scans DNA for error and binds to it

  2. MutH finds the hemimethylated cite (GATC sequence) closest to error and makes a nick n in the unmethylated strand (endonuclease activity)

  3. MutL linkes MutS and MutH and loops out a region of DNA

  4. exonuclease recruited to strip DNA from nick until slightly past error

  5. DNA polymerase III fills in the gap

  6. Ligase seals the nick

molecular spell check

reduces errors 100-fold

11
New cards

What happens to error frequency without proofreading or MMR?

error frequency increases 100 × 100 = 10,000 times without these mechanisms

One type of colon cancer is traced to mutation in MMR

12
New cards

What is done to address mutations that come from sources other than DNA replication (ex. chemical mutagens and high-intensity radiation)?

Nucleotide Excision Repair

13
New cards

Steps for nucleotide excision repair

  1. a complex of proteins detects an irregularity (ex. kink) in DNA

  2. an enzyme nicks DNA on both sides of damage

  3. DNA helicase unwinds and removes region of damaged bases

  4. DNA polymerase fills gap in 5’—3’

  5. Ligase seals gap

used to address mutations induced by chemical mutagens and UV radiation

14
New cards

2 Broad Categories of Mutation Types

  1. point mutations - small # BPs changed

  2. chromosomal-level mutations - large # BPs changes

15
New cards

2 Categories of Point Mutations

  1. Base substations

  2. Frameshift

16
New cards

Types of Base Substitutions

Affect protein coding genes:

  1. same sense - different codon, same amino acid

  2. missense - different codon, different amino acid

  3. nonsense - stop codon

transition - change one BP to another in same family

transversion - change one BP to another in a different family

17
New cards

Types of Chromosomal-level Mutations

  1. Insertion

  2. Deletion

  3. Translocation - swap sections between chromosomes

  4. Duplication - copy and paste

  5. Inversion - flip segment (no BPs lost)

18
New cards

How do base substitutions become permanent?

2 rounds of replication

  1. first round - BP mismatch happens

  2. second round - uncorrected mismatch is replicated (“cemened”)

19
New cards

How do different base substitution mutations affect final protein function?

same sense - no effect

missense - depends on replacement (can it do similar function? yes - some function, no -innactive)

nonsense - early truncation of protein, typically leads to loss of function

20
New cards

Sickle-cell anemia

Missense

Defective beta subunit in hemoglobin. Changes shape or red bloods cells and lessens its ability to carry oxygen. Helps against malaria because cells constantly remade in attempt to correct error.

21
New cards

Phenylketonuria (PKU)

Missense

Newborns screened to prevent mental impairment. Effect can be prevented by special diet. Can’t process phenylalanine which leads to toxic buildup (toxic to nerves) and low levels of tyrosine (inhibits normal growth and skin pigment)

22
New cards

Predicting Amino Acid Changes for Single Base Substitutions

  1. change first base - same relative position vertically

  2. change second base - same row

  3. change third base - same box

23
New cards

Define Frameshift Mutations and Explain Their Result and Effect on Protein Product

The addition or removal of a small number of bases not divisible by 3

They disrupt the normal reading frame, changing all subsequent codons

Typically leads to appearance of stop codon resulting in early truncation

24
New cards

Cystic Fibrosis

Removal of exactly 3 bases (one amino acid)

Results in faulty CFTR protein which removes chlorine from cells. Accumulation of Cl- in cells, do water doesn’t leave cell, dehydrating mucus layer

25
New cards

Lymphomas and Leukemias

Translocations

26
New cards

Oncogens

duplications

Cause them to become cancers

27
New cards

Fragile X syndrome

duplications

of short, repeated sequences

28
New cards

Huntington’s Disease

duplications

of short repeated sequences

29
New cards

Infertility

inversions

30
New cards

Haemophilia A

insertions

cause loss of clotting factor VIII

31
New cards

Duchenne’s Muscular Dystrophy

Deletion

32
New cards

Ames Test for Mutagenicity

Used to identify chemical mutagens

Dish 1: cells + growth medium + liver extract (conrtol - random mutation)

Dish 2: cells + growth medium + liver extract + chemical mutagen

Compare colonies that result. If Dish 2 has significantly more, it’s suspected the chemical mutagen causes mutation