Chapter 4.5-4.9 Molecular Biology

Question 1

Define Genetic Mutation

Answer 1

Any alteration of the DNA sequence of an organisms genome

Can be inherited or acquired

Question 2

Mutations passed onto offspring are called?

Answer 2

Germline mutations because they occur in germ cells which give rise to gametes

Question 3

Somatic Mutations

Answer 3

Occur in somatic (nongametic) cells and are not passed onto offspring but can have major effects on individuals

Question 4

Most common causes of mutations

Answer 4

most common: induced by environmental factor or chemical

Can be spontaneous

Question 5

Which is harder to repair: a single or double stranded DNA helix break?

Answer 5

A double stranded break (DSB) is much harder to repair

Means it has been split into 2 pieces

Single stranded break is easily patched because DNA helix is still held together in one piece

Question 6

UV light causes ___ damage to DNA. Explain.

Answer 6

photochemical damage

Ex if 2 pyrimidines are beside each other on a DNA backbone, UV light can covalently link them together

These pyrimidine dimers distort the DNA backbone and cause mutations during DNA replication if not repaired

Question 7

What do we call pyrimidines on a DNA backbone that have had photochemical damage done, fusing them?

Answer 7

Pyrimidine dimers : dimer is an oligomer consisting of two monomers joined by bonds that can be either strong or weak, covalent or intermolecular.

Question 8

Define mutagen

Answer 8

Any compound that can cause mutations

Question 9

Do chemicals always mutate DNA?

Answer 9

No, many chemicals interact with DNA directly. Many others turn into damaging agents as theyre being processed by cells

Chemicals can covalently alter bases or cause cross linking or strand breaks

Question 10

What do we call abnormal covalent bonds between varying parts of DNA?

Answer 10

Cross links

Question 11

What does it mean when a compound is intercalating?

What is an example of a compound that does this?

Answer 11

This is when Reactive Chemicals cause mutations

This is when compounds that look like purines or pyrimidines (Flat large aromatic ring structures) cause mutations because they insert themselves between base pairs and cause errors in DNA replication

Ethidium Bromide

Question 12

What are 3 things that cause mutations? Give an example of each.

Answer 12

1. Physical Mutagens: Ionizing radiation (Xray, alpha particles, gamma rays)
2. Reactive Chemicals: Intercalating compounds (Ethidium Bromide)
3. Biological Agents: Viruses, Transposons

Question 13

What is an example of a spontaneous mistake that results in Mutation? (hint: DNA polymerase )

Answer 13

When DNA polymerase makes mistakes in their proofreading and correction abilities

An incorrect bp may be missed and not repaired —> this error is passed down to all daughter cells

Spontaneous: therefore no mutagen

Question 14

How do viruses cause mutations in DNA?

Answer 14

An example of how biological agents can cause mutations

Lysogenic viruses insert into the genome of the host cell and cause mutations and disrupt genetic function

some viruses can cause cancer for this reason

Question 15

What are the 7 structural kinds of mutations?

Answer 15

1) Point mutations
2) Insertions
3) Deletions
4) Inversions
5) Amplifications
6) Translocations and rearrangements
7) Loss of heterozygosity

Question 16

Single base pair substitution mutation

Answer 16

Point Mutation

Question 17

What are Point Mutations

Answer 17

Mutation via single base pair substitution

Question 18

What are the 2 subtypes of point mutations?

What are the 3 types of point mutations?

Answer 18

Transitions (sub pyrimidine for pyrimidine or purine for purine)
or Transversions (Purine for/by pyrimidine)

a) Missense: one amino acid now replaced with coding for a different amino acid (not serious if similar amino acids like hydrophobe for hydrophobe)

b) Nonsense: a stop codon replaces a regular codon and prematurely shortens the protein

c) Silent: A codon is changed into a new codon but for the same amino acid so theres no change in protein amino acid sequence

Question 19

What is an insertion mutation?

What is a deletion mutation?

Both of these mutations can cause another type of mutation: ___?

Answer 19

a) addition of one or more extra nucleotides into the DNA sequence

b) The removal of nucleotides from the sequence

c) Both of these can cause a shift in the reading frame and cause frameshift mutations

Question 20

What are frameshift mutations? How serious are they?

Answer 20

Mutations that cause a shift in the way a frame is read

Very serious because they can terminate an incomplete polypeptide

Question 21

Are all insertions and deletions frameshift mutations?

Answer 21

No

If a whole codon is inserted or deleted, or several whole codons, it just adds or removes amino acids in the polypeptide, it does not change the reading frame

Question 22

For each type of mutation, does it involve a change in the genotype, the phenotype, or both?

Answer 22

By definition, all mutations involve a change in the genotype
(Genotype: the genetic constitution of an individual organism)

Most also cause a change in phenotype, but in conservative mutations it is a very subtle change that would be hard to detect
(phenotype: the set of observable characteristics of an individual resulting from the interaction of its genotype with the environment. )

Question 23

Explain Inversion mutation

Answer 23

When a segment of a chromosome is reversed end-to-end

Caused by breakage in the chromosome and rearrangement within itself

can be caused by transposons

Question 24

What three mutations can be caused by transposons ?

Answer 24

Insertions, Deletions, and inversions

Question 25

What is Chromosome amplification mutation? What process is it similar to?

Answer 25

When a segment is duplicated

Similar to Copy number variations

Question 26

Describe Translocation mutations

Answer 26

When recombination occurs between nonhomologous chromosomes
occurs when a chromosome breaks and the (typically two) fragmented pieces re-attach to different chromosomes.

Homologous chromosomes consist of alleles of the same gene type found in the same loci unlike non-homologous chromosomes, which constitute alleles of varying gene types.

Question 27

What are the two types of Translocation mutations?

What can this mutation cause between genes?

Answer 27

a) Can be balanced: no genetic info lost
or unbalanced: Genetic info is lost or gained

This can cause gene fusion: new gene product made from parts of 2 genes that were not previously connected (common in cancers)

Question 28

What are transposons?

Answer 28

mobile genetic elements in the genomes of both prokaryotes and eukaryotes

Mobile means these short segments can jump around the genome

Question 29

What are 3 common types of transposons?

Answer 29

IS element: The simplest one. structure: Transposase gene flanked on either sidde by inverted repeat sequences

Complex Transposons: Contain additional genes

Composite Transposons: Have 2 similar or identical IS elements with a central region in between

Question 30

What do all transposons have in common?

Answer 30

All of these have a Transposase gene to code for a protein enzyme called transposase

Question 31

What is Transposase? What does it do?

Answer 31

Transposase is a protein enzyme

It has cut and paste activity: it catalyzes mobilization of the transposon (excision from donor site) and integration into a new genetic location (acceptor Site)

It sometimes completely excises and moves transposon sequence, and sometimes its duplicated and moved while maintaining original location

Question 32

Explain the 3 steps in the mechanism of transposon mobilization

Answer 32

(1) Transposase gene codes for the “cut and paste” Transposase enzyme

(2) Transposase cuts a copy of the Transposon out of the original/ donor site

(3) The transposon mobilizes to a new recipient site, but a copy also stays at the donor site

Question 33

2 Transposons with the ____ direction can line up beside each other and cause chromosomal deletion. How?

Answer 33

Same direction

Recombination occurs between the transposons –> this causes deletion of DNA between the 2 transposons –> The original chromosome loses the DNA segment between the transposons (deletion)

Question 34

The segment of DNA lost takes 1 transposon with it. What kinds of issues can this cause?

Answer 34

The segment of DNA can jump with the transposon back into the genome somewhere, causing Chromosome Rearrangement

Question 35

If a chromosome has 2 transposons with inverted orientations, they can cause what?

Answer 35

They can pair and align with each other

After recombination, the sequence of DNA between the 2 transposons is inverted

Question 36

What is loss of heterozygosity?

Answer 36

Diploid organisms have 2 copies of each gene. A mutation in 1 copy is usually tolerated as long as the other copy is normal.

If deletion removes the normal gene, and the mutated gene is the only remaining copy, its called Loss of heterozygosity

Question 37

Diploid organisms have 2 copies of each gene. A mutation in 1 copy is usually tolerated as long as the other copy is normal.

If deletion removes the normal gene, and the mutated gene is the only remaining copy, its called ______?

Answer 37

Loss of heterozygosity