6.1 Cellular Control Flashcards
What is a gene mutation?
Change to DNA
How might they occur?
- randomly during DNA replication
- mutagenic agents such as UV light, tobacco, gamma rays etc
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
What is a silent point mutation?
- substitution of a base in a triplet but still coding for the same amino acid due to DEGENERACY
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
What is an example of a missense point mutation?
- sickle cell anaemia
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
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
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
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)
What is lac0?
operator region
What is lacZ?
codes for B-galactosidase
What is lacY?
codes for lactose permease
What is P?
promotor region where RNA polymerase binds to begin transcription
What is I?
when expressed, LacI repressor protein is coded for which binds to operator -> prevents RNA polymerase from binding and prevents transcription
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
