(6) Cellular Control

Question 1

Types of gene mutations

Answer 1

Substitution - one nucleotide is replaced with another.
Insertion - extra bases inserted into DNA.
Deletion - base pairs removed from sequence.

Question 2

Effects of mutations on protein production and function

Answer 2

Substitution can cause: a missense mutation - triplet code changes to a code for a different amino acid,
silent - triplet code changes to a different code for the same amino acid (degenerative),
nonsense - triplet code for amino acid changes to a stop codon, so translation stops.

Insertion or deletion can cause : a frameshift mutation - every triplet code after the point of insertion or deletion is altered, making a completely different protein.

Question 3

Possible effects of gene mutations

Answer 3

Neutral - no selective advantage to disadvantage (eye colour)

Harmful - decrease chance of survival (sickle cell anaemia)

Beneficial - increase chance of survival (peppered moth)

Question 4

Regulatory mechanisms that can control gene expression at the transcriptional level

Answer 4

Genes can be turned on or off by altering the rate of transcription, controlled by transcription factors which bind to the promotor region on DNA and it allows RNA polymerase to attach.
Increasing the rate = activators. Decreasing the rate = repressors.

Lac operon
Absence of lactose - regulator gene is transcribed and translated to make the repressor protein, it binds to the operator region and blocks the promotor region. So RNA polymerase cannot bind so structural genes are not transcribed - beta galactosidase and lactose permease are not made.

Presence of lactose - regulator gene makes repressor protein, lactose binds to it and changes its shape so it cannot bind to operator region. Allows RNA polymerase to bind and structural genes are made. mRNA from the genes are translated, so the cell makes lactose permease (to take lactose into the cell) and beta galactosidase (to hydrolyse lactose)

Question 5

Regulatory mechanisms that can control gene expression at the post transcriptional level

Answer 5

Transcription produces pre-mRNA which to modified to make mature mRNA.

Cap is added to 5’ tail which stabilises mRNA and delays degradation.
Splicing cuts RNA at specific points, introns are removed and exons are joined together.
RNA editing can occur to make different proteins from a single mRNA by using insertion, deletion or substitution.

Question 6

Regulatory mechanisms that can control gene expression at the post translational level

Answer 6

Modifying proteins that have been synthesised could involve the addition of non protein groups.

cAMP can activate the polypeptide as cAMP activates protein kinases and they add phosphate groups to proteins. Changes the tertiary structure and function of protein.

Question 7

Homeobox sequence

Answer 7

Code for transcriptional factors that regulate transcription by binding to DNA.
180 base pairs long and is highly conserved in plants animals and fungi.

Part of the protein it codes for - homeodomain - switches other genes on or off.

Homeobox genes determine the polarity of the body, segmentation and the position of different organs and limbs.

Hox gene - group of homeobox genes present in animals only.

Question 8

Mitosis and apoptosis in controlling development of body form

Answer 8

Hox genes regulate apoptosis and mitosis.

Mitosis is needed for growth and repair, checkpoints in mitosis prevent damaged cells from being produced.

Apoptosis is programmed cell death, cells are killed during development if they threaten survival.
Hydrolytic enzymes released inside cell break down the cytoskeleton, blebs form on cell membrane, nucleus fragments and cell breaks down into vesicles which are injected by phagocytes.
Important to produce the correct body plan.

Internal factors - DNA damage, cell signalling.

External factors - stress, lack of nutrients available, attack by a pathogen.