6.1 Cellular Control

Question 1

What is a gene mutation?

Answer 1

Change to DNA

Question 2

How might they occur?

Answer 2

• randomly during DNA replication
• mutagenic agents such as UV light, tobacco, gamma rays etc

Question 3

What is the difference between mutations in mitotic division and meiosis?

Answer 3

Mitotic -> cannot be passed, form cancerous tumours
Meiosis -> can be passed, in gamete formation

Question 4

What is a silent point mutation?

Answer 4

• substitution of a base in a triplet but still coding for the same amino acid due to DEGENERACY

Question 5

What is a missense point mutation?

Answer 5

• change to triplet causing DIFF amino acid sequence
• alteration of primary, etc, tertiary structure of protein -> might affect function

Question 6

What is an example of a missense point mutation?

Answer 6

• sickle cell anaemia

Question 7

What is a nonsense point mutation? What is an example?

Answer 7

• altering of a base triplet, so it becomes a stop codon
• truncated protein that will not function
• Duchenne muscular dystrophy

Question 8

What is an indel mutation? What is an example?

Answer 8

• nucleotide bases, NOT IN MULTIPLES OF 3, get inserted or deleted
• all subsequent triplets are altered due to overlapping nature of code + FRAMESHIFT
• primary, etc, tertiary structure altered.
• some forms of thalassemia

Question 9

What is the significance of an expanding triple nucleotide repeat? What is an example?

Answer 9

• number of repeats increases at meiosis and again from generation to generation
• Huntingtons: if CAG repeats go above a certain critical number

Question 10

If glucose is absent and lactose is present, what occurs?

Answer 10

• induces production of lactose permease (allows it to enter) and B-galactosidase (hydrolyses to galactose and glucose)

Question 11

What is lac0?

Answer 11

operator region

Question 12

What is lacZ?

Answer 12

codes for B-galactosidase

Question 13

What is lacY?

Answer 13

codes for lactose permease

Question 14

What is P?

Answer 14

promotor region where RNA polymerase binds to begin transcription

Question 15

What is I?

Answer 15

when expressed, LacI repressor protein is coded for which binds to operator -> prevents RNA polymerase from binding and prevents transcription

Question 16

What process occurs when lactose is present?

Answer 16

regulatory gene switches on and transcription of mRNA and then translation of repressor protein occurs

this binds to lactose, forming an inducer-repressor complex so it cannot bind to lac0 anymore

lacZ and lacY can therefore be transcribed into mRNA and this can be translated into the two required proteins to use lactase.

Question 17

What are transcription factors?

Answer 17

proteins/short non coding mRNA that bind to their specific promoter region, aid/inhibit RNA polymerase attachment, and activate/suppress transcription

Question 18

What are transcription factors involved with in eukaryotic cells?

Answer 18

• cell cycle (tumour suppressor + proto-oncogenes use them)

Question 19

What happens in post-transcriptional modification/gene regulation? What happens to the introns?

Answer 19

• full transcription unit including exons (coding) AND introns (non-coding) is transcribed into primary mRNA.
• splicing occurs to form the mature mRNA (introns removed, remaining exons joined together)
• some may become short lengths of non-coding RNA involved in gene regulation

Question 20

A length of DNA with introns and exons can…..

Answer 20

encode more than one protein, depending on the splicing (alternative splicing)

Question 21

What occurs in post-translational modification/gene regulation?

Answer 21

• activation of proteins via PHOSPHORYLATION

1) hormone/signal binds to receptor
2) G protein activated
3) adenyl cyclase activated
4) catalyses cAMP from ATP
5) cAMP activates PKA
6) phosphorylation of proteins occurs, activating many enzymes. uses ATP
7) using ATP, many also phosphorylate another protein such as CREB
8) CREB enters nucleus and acts as a transcription factor

Question 22

What is the homeobox gene sequence?

Answer 22

sequence of 180 base pairs in animals, fungi and plants

Question 23

What does the homeobox gene sequence encode for?

Answer 23

60 amino acid sequence called homeodomain sequence

Question 24

What is the structure and function of the homeodomain sequence?

Answer 24

can regulate transcription of adjacent genes involved in development

H-T-H (2 a-helices and one turn)
part of sequence recognises TAAT on enhancer region of gene to be transcribed

Question 25

What is significant about these sequences?

Answer 25

they have been CONSERVED: similarity in sequences extends across wide evolutionary distances

Question 26

What are Hox genes?

Answer 26

- only in animals - subset of homeobox genes that regulate development of embryos along ANTERIOR-POSTERIOR axis - clusters of up to 10 genes (tetrapods have 4 clusters) - encode homeodomain proteins: factors that can switch on cascades and promote cell division, apoptosis, etc.

Question 27

What is colinearity?

Answer 27

sequential and temporal order of gene expression corresponds to sequential and temporal development of body parts

Question 28

How are hox genes regulated?

Answer 28

- by gap and pair rule genes which are regulated by maternal mRNA from egg

Question 29

How is mitosis regulated?

Answer 29

- by Hox and homeobox genes

Question 30

What is apoptosis? What is the process?

Answer 30

PROGRAMMED CELL DEATH 1) enzymes break cytoskeleton 2) cytoplasm = dense 3) blebs form 4) chromatin condenses, DNA into fragments 5) vesicles ingested by phagocytic cells to avoid damage to others from debris

Question 31

How is apoptosis controlled?

Answer 31

cell signals e.g. cytokines, hormones, growth factors nitric oxide can induce it rate of cells dying should equal rate of cells produced

Question 32

Why are fruit flies chosen for research into genes controlling body plan development?

Answer 32

Low cost Simple body plan Rapid reproduction rate Development well understood

Question 33

Why are mice chosen as a suitable species for investigation also?

Answer 33

Low cost/ rapid reproduction OR development well understood More similar to humans Can show genetics are generalisable to more than one species

Question 34

Describe the general role of homeobox genes in the human body and suggest the roles of these genes in the development of the brain

Answer 34

GENERAL: - overall body plan determination - switch different genes on and off in diff cells, determining cell identity - regulate patterning and positioning of structures - active and expressed in ORDER during development - regulate levels of apoptosis and mitosis BRAIN: - determine anterior and posterior regions and therefore where brain and spinal cord will develop - expressed in a set order sequentially and temporally to determine regions of the brain, and neuronal organisation - switch genes on or off in the brain to form specialised neurones - regulate mitosis and apoptosis of neurones

Question 35

The yellow colour in peas is the result of an enzyme that breaks down chlorophyll, which is green. * The Y allele codes for the production of an enzyme that breaks down chlorophyll. * The y allele is the result of a mutation in the Y allele. * The y allele codes for an inactive form of this enzyme. (i)* Outline how the Y allele codes for the production of this enzyme and explain why the y allele codes for an enzyme with a different primary structure.

Answer 35

Genetic code (G)  DNA base sequence codes for amino acid sequence  reference to mRNA base sequence  triplet code / 3 bases = 1 amino acid  degenerate code  substitution could result in same amino acid Transcription (C)  transcription then translation  complementary base pairing  synthesis of mRNA strand  role of RNA polymerase Translation (L)  mRNA binds to ribosome  tRNA binds to mRNA  tRNA brings specific amino acid  mRNA translated into polypeptide Effect of y allele (M) substitution / frame-shift  different base sequence of DNA  different mRNA codon  different tRNA anticodon  tRNA brings different amino acid  different sequence of amino acids  amino acid sequence is primary structure

Question 36

In order for lactose to enter the cytoplasm of E coli a protein is required. The E coli living in the digestive system of young mammals are more likely to contain this protein than E coli living in the digestive system of old mammals. Suggest an explanation for this observation.

Answer 36

(mammal diet high in milk, so) high lactose concentration  (structural) gene for protein channel / lactose permease gene /lac Y , is , transcribed / expressed / switched on  (protein is) lactose permease 