6.1 - Cellular Control

Question 1

What is a mutation?

Answer 1

a mutation is a random change to the genetic material

Question 2

What is a gene mutation? and how can they affect a cell?

Answer 2

a gene mutation is a change to the DNA.

gene mutations may affect protein production or function.

Question 3

When and how can mutations occur?

Answer 3

mutations may occur spontaneously during DNA replication before cell division

certain chemicals can also cause mutations. chemicals can be mutagenic e.g. UV light or X-rays or tar in tobacco smoke.

Question 4

what does a mutation associated with mitosis mean for offspring?

Answer 4

mutations that are associated with mitosis are not passed on to offspring and may be associated with the development of cancerous tumours.

Question 5

what does a mutation associated with meiosis mean for offspring?

Answer 5

mutations that are associated with gamete formation and meiosis can be inherited by offspring.

Question 6

what are the 3 types of point mutation called?

Answer 6

1. silent
2. missense
3. nonsense

Question 7

what does a silent mutation mean?

Answer 7

a silent mutation involves a change to the base triplet where the triplet still codes for the same amino acid.
the structure of the protein is not affected - it basically has no impact.

Question 8

what does a missense mutation mean?

Answer 8

a missence mutation is a change to the base triplet sequence that leads to a change in the amino acid sequence.
this can result in a change in the structure of the protein produced, altering its shape and preventing it from performing its usual function.

Question 9

give an example of a disease caused by a missense mutation.

Answer 9

sickle cell anaemia

Question 10

what does a nonsense mutation mean?

Answer 10

a nonsense mutation causes the base triplet to become a stop triplet rather than a coding triplet. this is disruptive as it results in a protein that will not function.

the abnormal protein produced will most likely be degraded within the cell.

Question 11

give an example of a disease caused by a nonsense mutation.

Answer 11

muscular dystrophy

Question 12

what is a frame shift? and what is it caused by?

Answer 12

frameshifts are caused by insertions and deletions. single nucleotide bases are inserted or deleted into the gene. because the genetic code is non-overlapping and read in groups of all 3 bases, all of the subsequent base triplets are altered.

Question 13

what happens when a gene that has undergone insertion or deletion is translated?

Answer 13

when mRNA is translated from the gene, the amino acid sequence is severely disrupted.
the protein produced by the mRNA cannot carry out its normal function.

Question 14

what happens if a triplet of base pairs is inserted or deleted into the gene?

Answer 14

this DOES NOT cause a frameshift. it results in the addition/loss of an amino acid.

Question 15

what is an expanding nucleotide repeat?

Answer 15

some genes contain a repeating triplet of bases e.g. CAG, CAG, CAG.

in an expanding nucleotide repeat, the number of triplets that are repeating increases at meiosis and again from generation to generation.

Question 16

what diseases can result from an expanding nucleotide repeat?

Answer 16

huntingtons disease

Question 17

name some mutations that are not harmful, but instead are beneficial.

Answer 17

• blue eyes - harmful in areas with high light intensity as they can result in cataracts but are beneficial in areas of low light as they allow people to see better
• dark skin - melanin in the skin protects against harmful UV rays.

Question 18

how are enzymes synthesised in prokaryotic cells?

Answer 18

enzymes that are used for metabolic reactions are synthesised at a fairly consistent rate.
enzymes that are required under certain conditions are only synthesised at varying rates according to the needs of the cell.

Question 19

what happens when glucose is not present but lactose is in E-coli?

Answer 19

glucose is the normal respiratory substrate for E-coli. when glucose is not present, lactose induces the production of 2 enzymes:

1. Lactose permease - allows lactose to enter the bacterial cell.
2. beta - galactosidase - hydrolyses lactose

Question 20

what is an operon?

Answer 20

an operon is a set of genes that are used for transcription. they are under the control of an operator gene.
operons allow proteins to be synthesised in response to the needs of the cell e.g. enzymes to breakdown lactose

Question 21

name the different regions on the lac operon.

Answer 21

• the operator region = lac O
• the structural genes = lac Z and lac Y
• the promoter region = P
• the regulatory gene

Question 22

what do the structural genes do?

Answer 22

the structural genes code for the enzymes beta-galactosidase and lactose permease

Question 23

what does the promoter region do?

Answer 23

the RNA polymerase binds to the promoter region to begin transcribing for the enzymes.

Question 24

what happens when there is no lactose present in the culture medium?

Answer 24

the regulatory gene codes for the repressor protein which binds to the operator region. this prevents RNA polymerase from binding to the promoter region and therefore prevents the enzymes being made.

Question 25

what happens when lactose is added to the culture medium?

Answer 25

when lactose is added, molecules of lactose bind to the repressor protein molecules.
by binding to the repressor protein, lactose changes its shape and therefore prevents it from binding to the operator region.
the RNA polymerase can then bind and begin to synthesise enzymes.

therefore, lactose induces the synthesis of the proteins needed to break it down.

Question 26

in eukaryotic cells, what controls what genes are switched on or off?

Answer 26

transcription factors

Question 27

what do transcription factors do?

Answer 27

they slide along a pat of the DNA molecule and bind to specific promoter regions, aiding in the attachment of or inhibiting RNA polymerase.

• this activates or suppresses the transcription of a gene.

Question 28

why are transcription factors essential?

Answer 28

they are essential for the regulation of gene expression and ensure that the correct genes are activated or inhibited in different types of cells.

Question 29

what is an intron?

Answer 29

a non coding region of the DNA that is not expressed.

they help to separate the coding regions.

Question 30

what is an exon?

Answer 30

a coding or expressed region of the DNA.

Question 31

are introns transcribed even if they don’t code for anything?

Answer 31

the whole of the DNA including the introns are transcribed but the mRNA is edited to remove the introns. the remaining axons are then joined together.

Question 32

how are genes regulated post-translation?

Answer 32

genes are regulated by the activation of proteins. many genes are activated by being phosphorylated.

Question 33

what is a body plan?

Answer 33

a body plan is the general structure of an organism that are arranged in a certain way.

Question 34

what are hox genes?

Answer 34

hox genes are a set of genes that control the development of ANIMALS ONLY from the head to the tail (anterior to posterior).

Question 35

what are homeobox genes?

Answer 35

homeobox genes are a set of genes that control the development of specific body parts.
they are transcription factors which regulate the transcription of other transcription factors.

Question 36

what is the homeodomain sequence?

Answer 36

the homeodomain sequence is 180 base pairs long which means that it codes for 60 amino acids.
the homeodomain sequence can fold into a particular shape and bind to the DNA, regulating the transcription of other genes

Question 37

what is mitosis?

Answer 37

mitosis is the source of growth within organisms. it is controlled in development to control the size and position of structures.
e.g. the control of mitosis determines the formation and size of limbs

Question 38

what is apoptosis?

Answer 38

apoptosis is called programmed cell death. it is an intended process and occurs quickly.

Question 39

what is apoptosis used to prevent?

Answer 39

apoptosis is used to prevent cancerous growth when cells grow uncontrollably.

Question 40

name all of the kingdoms that use homeobox genes to control the development of their body plans

Answer 40

animals, fungi and plants

Question 41

why are homeobox genes highly conserved?

Answer 41

they are highly conserved because these genes are highly important.
a mutation to these genes would alter the body plan and many other genes would be affected.

Question 42

describe the sequence of events in apoptosis

Answer 42

1. enzymes break down the cell cytoskeleton
2. the cytoplasm becomes dense
3. the cell surface changes and small protrusions called blebs form.
4. chromatin condenses, the nuclear envelope breaks and the DNA breaks into fragments.
5. the cell breaks into vesicles that are ingested by phagocytic cells.

Question 43

how many times can normal body cells divide

Answer 43

normal body cells are limited to dividing a certain number - 50 - times before they die. this is known as the Hayflick constant.

Question 44

which genes regulate mitosis and why do they do this?

Answer 44

mitosis is regulated by Hox and Homeobox genes.

this regulation ensures the each new daughter cell contains the full genome and is a clone of the part cell

Question 45

how is apoptosis controlled?

Answer 45

apoptosis is controlled by cell signals that are released when genes involved in cell cycle regulation and apoptosis respond to internal and external stimuli.

Question 46

give some examples of signalling molecules involved in apoptosis.

Answer 46

cytokines from cells in the immune system.
hormones.
growth factors.

Question 47

why is apoptosis essential to development?

Answer 47

apoptosis is essential during limb development as it causes the digits to separate from one another.

not enough apoptosis = tumour formation
too much apoptosis = degeneration and cell loss