Cellular Control

Question 1

Define substitution mutation

Answer 1

A gene mutation where one nucleotide base is replaced by another

Question 2

Define an insertion mutation

Answer 2

A gene mutation where one or more nucleotide bases are added into the DNA sequence

Question 3

Define a deletion mutation

Answer 3

A gene mutation where one or more nucleotide bases are removed from the DNA sequence

Question 4

Define a point mutation

Answer 4

A gene mutation that affects a subtle nucleotide base in the DNA sequence

Question 5

Define a frame shift mutation

Answer 5

A gene mutation caused by the insertion/deletion if nucleotide bases that isn’t in a multiple of 3

Question 6

Define a non sense mutation

Answer 6

A point mutation where a base change converts a codon originally coded for an amino acid into a stop codon

Question 7

Define a missense mutation

Answer 7

A point mutation where a base change results in a codon that codes for a different amino acid

Question 8

Define a silent mutation

Answer 8

A point mutation where a change in the base sequence does not alter the primary structure

Question 9

What are mutagenic agents

Answer 9

Things that cause extra mutations

Question 10

Give the benefits of mutations

Answer 10

Evolution (selective advantage) - e.g., sickle cell gives immunity to malaria

Question 11

Give the harms of mutations

Answer 11

Genetic diseases
Cancer

Question 12

Give examples of mutagens

Answer 12

UV/ionising radiation
Chemicals
Viruses

Question 13

What feature of DNA molecule is changed as a result of a mutation

Answer 13

Nucleotide bases

Question 14

Which feature of the genetic code means that a substitution may have no effect on the amino acid sequence

Answer 14

Degenerate - many amino acids are coded for by more than one triplet a

Question 15

What are transcription factors

Answer 15

Proteins that bind to specific DNA sequences to initiate the transcription of genes into mRNA

Question 16

What does it mean when a gene is ‘switched off’

Answer 16

Transcription factors cannot bind to the DNA - prevents transcription process and so the synthesis of polypeptides

Question 17

Define an operon

Answer 17

A cluster of genes controlled by a single promoter, allowing for coordinated expression

Question 18

What is the lac operon

Answer 18

A cluster of genes in E Coli bacteria which controls the metabolism of lactose

Question 19

What is the function of lacI

Answer 19

Codes for repressor protein that can inhibit and control the lac operon activity

Question 20

Role of lacZ

Answer 20

Codes for B-galactosidase
Breaks down lactose into glucose and galactose

Question 21

Role of lacY

Answer 21

Codes for lactose permease
Transports lactose into the cell

Question 22

How does the lac operon function when lactose is absent

Answer 22

• repressor protein binds to operator region
• RNA polymerase is blocked from the promoter region
• RNA polymerase can’t transcribe the structural genes
• enzymes for lactose metabolism aren’t produce

Question 23

How does the lac operon function when lactose is present

Answer 23

• lactose binds to repressor protein
• Repressor protein changes shape and is released from the operator region
• RNA polymerase can bind to the promoter region and initiate transcription
• RNA polymerase transcribes the structural genes, leading to the production of enzymes necessary for lactose metabolism

Question 24

How does glucose regulate the lac operon

Answer 24

Through the signalling molecule cyclic AMP (cAMP)

Question 25

How does cAMP function when both glucose and lactose are present

Answer 25

- glucose reduces cAMP levels - cAMP cannot form a complex with its receptor protein - the lac operon’s transcription is downregulated - lactose metabolism enzymes are not produced

Question 26

What are introns

Answer 26

The non coding regions of DNA which are removed from pre-mRNA after being transcribed

Question 27

What are exons

Answer 27

Coding regions which are joined together to form mature mRNA

Question 28

What is splicing

Answer 28

Process where introns are removed and exons are joined together, providing instructions for the protein sequence

Question 29

What are homeobox genes

Answer 29

Group of regulatory genes with a conserved DNA sequence that guides the development of body plans

Question 30

What is a homeobox sequence

Answer 30

Highly conserved DNA sequence found within homeobox genes that is crucial for the development of an organisms body plan

Question 31

What are hox genes

Answer 31

A subset of homeobox genes in animals containing homeobox sequences essential for the correct positioning of body parts

Question 32

How do hox genes control development

Answer 32

- homeobox sequences encode the homeodomain (part of protein that binds to DNA) - homeodomain operates as a transcription factor - it binds to DNA, switching developmental genes on or off - this modifies the transcription of proteins necessary for the development of body plans

Question 33

Why are homeobox genes so conserved

Answer 33

A mutation would have large affects by altering the organisms body plan Mutations are likely to be lethal and selected against

Question 34

Why are fruit flies often used in studies on genes that control body plan

Answer 34

- fewer ethical concerns than other animals - low cost - genetics and development are well understood - rapid reproduction rate - simple body plan - mutations can be studied with a low powered microscope

Question 35

Define apoptosis

Answer 35

controlled and programmed cell death - involves cell fragments being engulfed by phagocytes and destroyed