Mutations

Question 1

Mutation

Answer 1

Changes in the DNA that replace, insert, or delete nucleotides

Question 2

Mutations are the ultimate source of…

Answer 2

All new genes and the genetic diversity of life

Question 3

2 main categories of mutations

Answer 3

1) Large Scale
2) Small Scale

Question 4

Large Scale Mutations

Answer 4

Affect long segments of DNA

(chromosomal rearrangement)

Question 5

Small Scale Mutations

Answer 5

Affect one or a few nucleotide pairs

Question 6

Mutations can alter phenotypes by…

Answer 6

Impacting gene product sequence or expression

–> Altering levels of mRNA + proteins or the STRUCTURE of these molecules

Question 7

Mutations in Non-Coding Regions of DNA

Answer 7

Don’t impact structure/function of gene products but instead alter gene expression and regulation

Question 8

Most mutations are within the…

Answer 8

Non-coding region of DNA

Question 9

Germ Cell Mutations

Answer 9

Inherited between generations

Question 10

Somatic Cell Mutations

Answer 10

Not inherited

–> But can cause serious problems for people when cells with a mutation proliferate (= cancer)

Question 11

What factors determine phenotypic effect of a mutation?

Answer 11

1) The type of cell
2) When in the life cycle the mutation occurs (the earlier the more severe its effects)
3) The dominance of a mutation

Question 12

Point mutations

Answer 12

Changes in a single nucleotide pair of a gene (single base pair change)

Question 13

2 main types of point mutations:

Answer 13

1) Substitutions
2) Deletions/Insertions

Question 14

Substitution Mutations

Answer 14

The replacement of one nucleotide and its partner with another pair of nucleotides

Question 15

Types of substitution mutations

Answer 15

1) Missense
2) Nonsense
3) Silent

Question 16

Missense Mutations

Answer 16

Change of ONE codon for another which results in a change in the amino acid

–> Causes change in a SINGLE POINT!!!

SUBSTITUTIONS

Question 17

Mutation in Sickle Cell Anemia

Answer 17

Missense mutation (in hemoglobin)

(A shift from an “a” to a “t”)

Wild type cells = Produce glutamic acid (- charge) at that position

Mutated cells = Produce VALINE (neutral charge) at that position

–> **Replacement of glutamic acid with valine

Question 18

In sickle cell anemia, what leads to the formation of sickled cells?

Answer 18

The change in the charge of hemoglobin thanks to the replacement (substitution) of glutamic acid (+) by valine (neutral) affects its STRUCTURE

–> Hb forms needle like aggregates within RBCs, giving them their sickled shape

Question 19

Nonsense Mutation

Answer 19

PREMATURE STOP CODON –> Termination of polypeptide happens earlier than it should

Question 20

How does a nonsense mutation impact the final polypeptide product?

Answer 20

It shortens it

–> the resulting polypeptide will be shorter and incomplete

Question 21

Severity of the effect of a nonsense mutation is dependent upon:

Answer 21

Where(“/when”) in the sequence the mutation occurs

–> At the end = almost entire protein is produced normally (less severe)

–> At the beginning = almost no protein is produced (more severe)

Question 22

Silent Mutations

Answer 22

Substitutions that have no effect on amino acid sequence!

Question 23

Why are silent mutations possible?

Answer 23

Redundancy of the genetic code (multiple codons call for the same amino acid)

Question 24

Although silent mutations don’t have protein sequence, they can still have an effect on phenotype if…

Answer 24

The codon change alters “translation efficiency”

–> Most organisms have “codon bias” and are used to dealing with specific codons for amino acids

–> Can affect rate of translation if the new codon is not “preferred” by the cell

Question 25

Insertions/Deletions

Answer 25

Additions or deletions of nucleotide pairs in a gene

Question 26

What do insertions and deletions alter?

Answer 26

The reading frame

Question 27

Frameshift mutations occur when there is…

Answer 27

An insertion or deletion of a number of nucleotides that is NOT divisible by 3

Question 28

What regions of a protein are altered by insertions and deletions that are frame shifting?

Answer 28

Protein sequence DOWNSTREAM the insertion or deletion will be different from the original protein

Question 29

Severity of insertions/deletions depends on…

Answer 29

Where in the sequence the mutation occurs

–> Closer to beginning = more incorrectly read AAs = greater severity

Question 30

Insertion and deletions cause…

Answer 30

Frameshift

Question 31

Insertions and deletions ARE NOT ______________ mutations

but instead are _________________ mutations

Answer 31

1) Are NOT nonsense or missense mutations

2) ARE FRAMESHIFT mutations