Unit 6.1- Cellular Control

Question 1

Types of point mutations:

Answer 1

• Silent mutations
• Nonsense mutations
• Missense mutations

Question 2

Silent mutations:

Answer 2

• Change to the base triplet but the triplet codes for the same amino acid
• The primary structure, and therefore the tertiary structure, is not altered

Question 3

Missense mutations:

Answer 3

• A change to the base triplet causes a different amino acid to be coded for
• Could have a significant effect on the protein produced
• The alteration to the primary structure leads to a change in the tertiary structure, altering its shape and preventing it from carrying out its usual function

Question 4

Nonsense mutations:

Answer 4

• A mutation alters a base triplet so that it becomes a stop triplet
• Results in a truncated protein that will not function
• The protein will most likely be degraded in the cell

Question 5

Types of indel mutations:

Answer 5

• Insertions and deletions

- Expanding triple nucleotide repeats

Question 6

Insertions and deletions:

Answer 6

• Causes a frame shift (as long as bases are not inserted or deleted in multiples of three)
• All subsequent base triplets are altered
• The primary structure and therefore the tertiary structure of the protein is dramatically altered, meaning the protein cannot carry out its usual function
• If the protein is abnormal, it will be rapidly degraded in the cell

Question 7

Expanding triple nuceotide repeats:

Answer 7

• Some genes contain a repeating triplet
• In expanding triple nucleotide repeats, the number of the repeated triplet increases at meiosis, and again from generation to generation

Question 8

Exon definition:

Answer 8

The coding or expressed region of DNA

Question 9

Intron definition:

Answer 9

The non-coding region of DNA

Question 10

Operon definition:

Answer 10

A group of genes that function as a single transcription unit

Question 11

Transcription factor definition:

Answer 11

Protein or short non-coding RNA that can combine with a specific site on a length of DNA and inhibit or activate transcription of a gene

Question 12

What does E. coli metabolise if glucose is absent?

Answer 12

• Lactose if it is present
• Lactose induces the production of two enzymes:
• Lactose permease, which allows lactose to enter the bacterial cell
• Beta galactosidase, which hydrolyses lactose to glucose and galactose

Question 13

What is the Lac operon?

Answer 13

• Length of DNA about 6000 base pairs long.
• Contains the following regions:
• Regulatory gene
• Promoter region (control site)
• Operator region (control site)
• LacZ (structural gene)
• LacY (structural gene)

Question 14

What do lacZ and lacY code for?

Answer 14

• B galactosidase

- Lactose permease

Question 15

How does the lac operon work in the absence of lactose (when there is glucose)?

Answer 15

• Regulatory gene I codes for repressor protein (lacI)
• Repressor protein binds to operator, preventing RNA polymerase from binding to the promoter region
• Repressor protein therefore prevents the genes LacZ and LacY from being transcribed
• The genes for lactose metabolism are not made
• The genes are ‘switched off’

Question 16

How does the lac operon work in the absence of glucose and when there is lactose?

Answer 16

• Molecules of lactose bind to the LacI repressor protein, altering the shape of the LacI repressor, preventin git from binding to the operator.
• The RNA polymerase enzyme can then bind to the promotor region and begin trnascribing the structural genes into mRNA that will then be translated into the two enzymes.
• Thus, lactose induces the enzymes needed to break it down

Question 17

How do transcription factors work?

Answer 17

They slide along a part of the DNA molecule, seeking and binding to their specific promoter regions. They may then aid or inhibit the attachment of RNA polymerase to the DNA, and activate or suppress transcription of the gene

Question 18

What is primary mRNA?

Answer 18

mRNA where all the DNA of the gene has been transcribed, including the introns. The introns are then removed through splicing and the exons are joined together

Question 19

Apoptosis definition:

Answer 19

Programmed cell death

Question 20

Conserved definition:

Answer 20

Has remained in all descendant species throughout history

Question 21

Homeobox sequence definition:

Answer 21

Sequence of 180 base pairs (excluding introns), found within genes that are involved in regulating patterns of anatomical development in animals, fungi and plants

Question 22

Hox genes definition:

Answer 22

Subset of homeobox genes, found only in animals; involved in formation of anatomical features in correct locations of body plan

Question 23

What is a homeodomain sequence?

Answer 23

• The 60 amino acids coded for by the 180 DNA base pairs in the homeobox sequence
• The homeodomain sequence can fold into a specific shape and bind to DNA, and regulate the transcription of adjacent genes
• Transcription factors

Question 24

What shape do homeodomain-containing proteins fold into?

Answer 24

H-T-H (alpha helix, turn alpha helix)

Question 25

What sequence of bases does part of the homeodomain amino acid sequence recognise?

Answer 25

TAAT (on the enhancer region of a gene that needs to be transcribed)

Question 26

What are hox genes involved in in the development of an embryo?

Answer 26

- Expressed in order along the anterior-poterior axis of the developing embryo - Sequential and temporal gene expression

Question 27

How does apoptosis happen?

Answer 27

- Enzymes break down the cell cytoskeleton - The cytoplasm becomes dense with tightly packed organelles - Cell surface membrane changes and small protrusions called blebs form - Chromatin condenses, nuclear envelope breaks and DNA breaks into fragments - The cell breaks into vesicles that are ingested by phagocytis cells, so that cell debris does not damage any other cells or tissues - The whole process happens quickly