Chapter 8

Question 1

Mutation

Answer 1

A change in the nucleotide sequence of DNA that results in a recognizable change in the organism; an altered mRNA sequence, which will possibly result in the formation of the incorrect protein synthesis

Question 2

Substitution

Answer 2

A type of mutation where one nucleotide is replaced with another of a different base:
CGT (codes for alanine) —mutation—> (A)GT (codes for serine)

Question 3

Removal (Deletion)

Answer 3

A type of mutation that occurs when one nucleotide is removed randomly and not replaced with another nucleotide:

• a gene: CGT, GCA GTT, T__,… codes for alanine, arginine, glutamine
• A removed: CGT, GCG, TTT… codes for alanine, arginine, lysine

Question 4

Addition (Insertion)

Answer 4

A type of mutation that occurs when a nucleotide is added randomly:

• a gene: CGT, GCA, GTT… codes for alanine, arginine, glutamine
• addition: CGT, G(A)C, AGT… codes for alanine, eucine, serine

Question 5

Thymine Dimers

Answer 5

A type of mutation that occurs when two adjacent thymine bases form a covalent bond between them and distort the double helix, damaging the DNA; caused by exposing DNA to UV or X-rays

Question 6

Cellular Effects of Mutation

Answer 6

• Death: most are detrimental
• Benefit: some provide a benefit (increased antibiotic resistance)
• No change: some will not change the protein constructed or only affect a portion of the chromosome that is not important

Question 7

Spontaneous Mutation

Answer 7

Occurs randomly during DNA replication (occurs 1 in 10,000 to 1 in 1,000,000,000 replications for every single gene)

Question 8

Induced Mutation

Answer 8

DNA is exposed to mutagens

Question 9

Mutagens

Answer 9

A physical or chemical agent that causes changes to genetic material; increase the risk of mutations by 10-1000X

Question 10

Light Repair

Answer 10

Type of thymine dimer repair in which cells that possess the enzyme photolyase will repair these mutations when exposed to visible light; the enzyme breaks the covalent bonds between the thymines

Question 11

Dark Repair

Answer 11

Type of thymine dimer repair in which visible light is not necessary; one enzyme compares the complementary strand of DNA and finds and removes the mutation; DNA polymerase replaces the correct base back into the DNA sequence

Question 12

Proofreading by DNA Polymerase

Answer 12

This enzyme compares what base was incorporated to the template, if the bases are not complementary, then the correct base is incorporated into the new strand

Question 13

Mismatch Repair

Answer 13

If DNA polymerase misses a wrong base, the another back-up system is used to repair mutations - Ultraviolet light repair system

Question 14

Ultraviolet Light Repair System (Uvr)

Answer 14

• Two Uvr A proteins and one Uvr B (trimer) attach to the DNA molecule then move down the molecule scanning for damage
• Once damage is found, the trimer stops and the two Uvr A proteins are released; Uvr B remains
• Uvr C attaches to the Uvr B anc uts the DNA on both sides of the damaged DNA several nucleotides away
• Uvr D (a DNA helicase) releases the segment of DNA and Uvr B, C, and D are released
• The DNA sequence that now needs to be replicated is filled in with complementary nucleotides using DNA polymerase and is sealed with DNA ligase

Question 15

Transformation

Answer 15

A method of gene transfer in which bacterial cells take up naked DNA molecules; conducted by both gram+ and gram- organisms; Griffith’s mice experiment

Question 16

Competent Bacteria

Answer 16

Cells that have large holes that allow pieces of DNA (20 genes) to enter the cell

Question 17

Natural Competence

Answer 17

Under certain environmental conditions or certain bacteria (soil microbes), a cell will be competent

Question 18

Artificial Competence

Answer 18

Use of an electrical current to create large holes

Question 19

Transduction

Answer 19

The most common type of gene transfer that occurs in every bacteria cell:

• A bacteriophage enters a bacteria cell, uses deoxyribonuclease to digest the chromosome into small pieces; the DNA or RNA of the virus is also replicated
• Some sections of the bacteria chromosome are integrated into the new viruses
• The viruses leave the infected bacterial cell and deposit the bacterial DNA section into a new bacterial cell

Question 20

Bacteriophage

Answer 20

A virus that infects and replicates within bacteria

Question 21

Conjugation

Answer 21

A type of gene transfer that is uncommon and requires physical contact between bacteria; occurs mostly in gram- bacteria:
- Plasmids replicate and then are transferred from donor to recipient cells (only in one direction) using pili

Question 22

Plasmid

Answer 22

Small, circular DNA molecule that is physically separate from, and can replicate independently of, chromosomal DNA within a cell

Question 23

Donor (F+) Cells

Answer 23

Contain the genes on the plasmid that code for the pilus and the ability to be able to transfer DNA to other cells (F stands for fertility)

Question 24

Recipient (F-) Cells

Answer 24

No plasmid that codes for pilus; can only receive plasmid; once mixed, will become F+

Question 25

R Factor Plasmid

Answer 25

Contains multiple genes that give the plasmid holder resistance to a series of different kinds of antibiotics and even some heavy metals; very important to the medical profession

Question 26

Hfr (High Frequency Recombination)

Answer 26

Plasmids can occasionally be incorporated into the bacterial chromosome; whole bacterial chromosomes can be transferred but it takes a very long time

Question 27

Common Features of the Three Methods of Gene Transfer

Answer 27

• Only a few genes transferred at once (portions of chromosomes or plasmids)
• Once inside the cell, new genes are incorporated into the bacterial chromosome by the same method: breakage-cleavage
• Incorporation of gene only successful 1% of the time

Question 28

Breakage-Cleavage

Answer 28

Method in which new genes are incorporated into a bacterial chromosome:

• Corresponding homologous genes are paired together (side by side)
• An enzyme (deoxyribonuclease) will remove the “old” gene
• Another enzyme (DNA ligase) will join the “new” gene to the recipient’s chromosome
• Recipient gene is destroyed by enzymes