6.1 Cellular Control Flashcards by Eva x

What is a gene mutation?

Change to DNA

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How might they occur?

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

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

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

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What is a silent point mutation?

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

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What is a missense point mutation?

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

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What is an example of a missense point mutation?

sickle cell anaemia

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

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

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What is an indel mutation? What is an example?

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

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

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

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

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

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What is lac0?

operator region

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What is lacZ?

codes for B-galactosidase

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What is lacY?

codes for lactose permease

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What is P?

promotor region where RNA polymerase binds to begin transcription

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What is I?

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

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What process occurs when lactose is present?

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.

What are transcription factors?

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

What are transcription factors involved with in eukaryotic cells?

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

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

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

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

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

What occurs in post-translational modification/gene regulation?

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

What is the homeobox gene sequence?

sequence of 180 base pairs in animals, fungi and plants

What does the homeobox gene sequence encode for?

60 amino acid sequence called homeodomain sequence

What is the structure and function of the homeodomain sequence?

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

What is significant about these sequences?

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

What are Hox genes?

- 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.

What is colinearity?

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

How are hox genes regulated?

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

How is mitosis regulated?

- by Hox and homeobox genes

What is apoptosis? What is the process?

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

How is apoptosis controlled?

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

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

Low cost Simple body plan Rapid reproduction rate Development well understood

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

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

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

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

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.

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

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.

(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 