Genetics of living systems

Question 1

mutation

Answer 1

a random change is the sequence of DNA bases within a gene or in the structure of a chromosome

Question 2

ionising radiation - factor increasing the probability of a gene mutation

Answer 2

can break DNA strands and mutation occurs during the repair process
- deaminating chemicals - converts one base to another
- alkylating agents - add methyl or ethyl groups to a base resulting in incorrect pairings
- base analogs

Question 3

deaminating chemicals - factor increasing the probability of a gene mutation

Answer 3

converts one base to another

Question 4

alkylating agents - factor increasing the probability of a gene mutation

Answer 4

add methyl or ethyl groups to a base resulting in incorrect base pairing

Question 5

base analogs - factor increasing the probability of a gene mutation

Answer 5

derivatives of original bases which are incorporated into DNA instead of them

Question 6

viruses - factor increasing the probability of a gene mutation

Answer 6

viral DNA inserted into a host genome and is replicated instead of DNA

Question 7

effects of mutations

Answer 7

• no effect - due to degenerate nature of genetic code - doesn’t offer selection advantage or disadvantage
• damaging - phenotype affected as non-functional proteins synthesized or proteins not synthesised at all
• beneficial - proteins synthesised that offer an adaptive trait

Question 8

types of mutations

Answer 8

insertion or deletion - causes a frameshift as DNA is read in a non-overlapping way
- substitution - no frameshift, may still code for the same amino acid

Question 9

missense mutation

Answer 9

changes the amino acids that are incorporated into the polypeptide

Question 10

nonsense mutation

Answer 10

introduces a stop codon into the genetic code so protein does not finished being synthesised

Question 11

types of chromosome mutations

Answer 11

• deletion - sections of chromosome break off and are lost
• duplication - sections are repeated
• translocation - a section of a chromosome breaks off and joins another non-homologous chromosome
• inversion - a section of a chromosome breaks off, reversed then reattaches
• whole chromosome - entire chromosome is lost or replicated eg. Down’s syndrome due to extra chromosome 21

Question 12

heterochromatin

Answer 12

• EUKARYOTES
• DNA very tightly wrapped around histones
• DNA not accessible for transcription so this section of DNA is not needed for the protein

Question 13

euchromatin

Answer 13

• EUKARYOTES
• DNA loosely wrapped around histones
• DNA accessible to enzymes for transcription so this section of DNA is needed for the protein

Question 14

acetylation

Answer 14

• EUKARYOTES
• acetyl group added, neutralises the charge on the histone tails causing DNA to wrap loosely around histones so the gene can be transcribed
• causes gene expression

Question 15

methylation

Answer 15

• EUKARYOTES
• methyl group added, maintains positive charge on histone tails causing DNA to wrap tightly around histones
• causes gene silencing

Question 16

what is epigenetics?

Answer 16

• our environment can change gene expression without the DNA code itself being changed
• acetyl or methyl groups can be altered by enzymes
• this is reversible
• changes can be inherited or acquired throughout life

Question 17

structural gene

Answer 17

• PROKARYOTES
• codes for enzymes
• Z - gene that codes for Beta-galactosidase
• Y - gene that codes for lactose permease

Question 18

regulatory gene

Answer 18

• PROKARYOTES
• codes for a repressor protein that prevents transcription of structural genes (Z and Y) - switches them on/off

Question 19

when is the lac operon switched on?

Answer 19

• PROKARYOTES
• when glucose is in short supply but lactose is present, lactose can be used as a respiratory substrate

Question 20

enzymes coded for by the lac operon

Answer 20

• PROKARYOTES
• lactose permease - makes membrane more permeable to lactose - transported into cell (transmembrane symport protein)
• galactosidase - hydrolyses lactose into glucose and galactose

Question 21

operator region

Answer 21

• PROKARYOTES
• switches Z and Y genes on/off

Question 22

promoter region

Answer 22

• PROKARYOTES
• binding site of RNA polymerase for transcription of Z and Y
• can be blocked or not

Question 23

lac operon if glucose is present and lactose is absent

Answer 23

• PROKARYOTES
  1. regulatory gene is expressed and synthesis of repressor protein occurs
  2. repressor protein binds to operator region
  3. repressor protein partially covers promoter region
  4. RNA polymerase can’t bind - Z and Y genes can’t be transcribed - no enzymes produced