1
Q
What is a mutation?
A
- a random change in DNA sequence (simples….)
2
Q
3 main types of Genetic Mutations and Effects to organisms..!
A
- Substisution/Point Mutation = base pair subbed for another
- Insertion/Addition Mutation = addition of nucleotide base
- Deletion Mutation = loss of nucleotide base
- Harmful = cancers, CF…, Neutral = smells, earlobe shape, Beneficial = evolution, natural selection…
3
Q
3 types of Point mutation!
A
- Silent = no AA change, due to DNA degeneracy > no change in protien primary/tertiary structure
- Missense = base triplet sequence change > change in AA in protien
- Nonsense = changes AA into a STOP codon, truncating the protien length > improper folding and no function..
4
Q
Explain how Insertions/Addition and Deletion mutations cause FrameShift!
A
- I/A: added base will case ALL following bases to be modified = reading frame shift RIGHT by 1
- D: lost base will cause reading frame shift by 1
- BOTH may also cause truncation of base sequence as a result ….
5
Q
What is a nucleic acid?
A
- these are polymers of nucleotides!
- includes = DNA and RNA
6
Q
Features of non-coding DNA??
A
- rRNA / tRNA synthesis!
- Increases/decrease of gene expression (lac operon logic…)
7
Q
What are Transcription Factors, and method of transcription control..?
A
- These are proteins that bind to specific regions of DNA to control gene transcription!
- Will bind to RNA polymerase, and binds to DNA site to intitate transcription of certain protein… (Transcription Initation Complex)
- Inhibitor molecules can bind to DNA sites > prevents transcription factors to bind = NO TRANSCRIPTION
8
Q
Define operon
A
- a group of genes expressed at SAME TIME and functions as a single transcription unit! (one same gene regulatory system)
9
Q
What are REGULATORY and STRUCTURAL genes?
A
- Reg = gene that produces transcription factors to control transcription of protiens / turn other genes ON or OFF
- Struc = genes coding for structure of enzymes/polypeptides of any protien!
- Hence, regulatory genes control expression of structural genes…!
10
Q
General purpose of the Lac Operon??
A
- TRANSCRIPTIONAL level modification”
- Prokaryotes (e.g. E.Coli) normally respires glucose molecules
- However, If lactose presence is available, LACTOSE is metabolised…
- Hence, lactose presense induces production of the 2 enzymes: β-galactosidase and lactose permease……
11
Q
Structure of Lac Operon…
A
- Σ 6 segments in operon
- Regulatory Region! (of Lac Operon transcription): Lac I = encodes Lac Repressor Protien, Promoter = RNA polymerase binding site, Lac O = Lactose Repressor Protien binding site
- Structure Genes (actual DNA coding section): Lac Z = encodes β-galactosidase [lactose hydrolysis] , Lac Y = lactose permease [Lactose transport into cell], Lac A = encodes transacetylase
12
Q
What occurs when Lactose is NOT PRESENT in prokaryotic cell?
A
- Lac I (regulatory gene) continually transcribes and translates Lac Repressor protein
- The Lac Repressor Protein binds to the operator region (Lac O) neighbouring lac Z
- Due to repressor protein presence, RNA polymerase CAN’T BIND to promoter region
- NO TRANSCRIPTION of structural genes (down regulated operon)
- No enzyme is synthesised….
13
Q
What occurs when Lactose is PRESENT in prokaryotic cell?
A
- Uptake of lactose by the bacterium…
- Lactose binds to binding site on Lactose Repressor Protein, changing 3D tertiary shape = can’t bind to the operator (Lac O)
- RNA polymerase NOW able to bind to the promoter region = transcription takes place!
- The mRNA from all three structural genes is translated
- cAMP binds to RNA polymerase = increases transcription rate!
- Enzyme β-galactosidase is produced = lactose broken down for respiration by bacterium!
14
Q
Example of post-transcriptional modification (control of genes?)
A
- after transcription, primary mRNA is produced, contains introns (non-coding genes for protien) and exons (coding genes!)
- Splicing occurs = the removing of introns primary mRNA joining together exons to produce final, mature mRNA!
- Ready to enter translation…..
15
Q
How can DNA genes encode for more than 1 protien?
A
- During splicing of introns away from exons, these exons can join together in diff combinations and lengths, or some not used at all!
- Hence, different translated protien, due to different exon arrangement!
16
Q
Example of post-translational modification (control of genes?)
A
- Hormone as 1st messenger CAN NOT pass through phospholipid bilayer [non lipid soluble] = binds to cell surface RECEPTORS!
- G-protien is activated, then activating adenyl cyclase = converts ATP to cAMP
- cAMP as 2nd messenger causes Protien Kinase activation/phosphorylation…
- Activated proteins with CHANGED SHAPES may enter nucleus via nuclear pore = acts as transcription factor!
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17
Q
Why may non-coding regions of DNA have large variation?
A
- these are not selected against during natural selection!
- no phenotypic advantage/disadvantage to random mutations that may develop…
18
Q
Define Morphogenesis…
A
- the development of correct anatomical features in the correct places of an organism!
19
Q
What is a Homeobox
A
- Homeobox = DNA sequence that codes for a protein transcription factor
- These transcription factors (that homeobox sequences code for) attach to DNA at specific regions regulating gene transcriptions by TURNING DIFFERENT GENES on/off in the CORRECT ORDER!
- Hence, genes will aslo be EXPRESSED in order, whilst regulating apoptosis/mitosis rate during development
20
Q
Define Homeobox Gene and Key Properties!…
A
- This is any gene that contains a homeobox sequence!
- This sequence is 180 base pairs long, hence codes 60 amino acids on homeodomain
- Will code for amino acids that produces transcription factors, the DNA-binding regions of which must all have the same shape (coded part by the sequence = homeodomain!)
- Homeobox gene sequences in plants, animals and fungi are SIMILAR and HIGHLY CONSERVED = have been seleced for by natural selection!
- Mutations that affect homeobox sequences can lead to organisms that are not viable so they are selected against by natural selection….
21
Q
What is the general purpose of Homeobox Genes?
A
- Responsible for the genetic control of the development of body plans in different organisms!
- Helps to form the basic pattern of the body
- For example, they control the polarity of the organism (which end will develop into head/tail)
- Controls the segmentation of organisms into distinct body parts such as wings and limbs/organs present in each section of the body
22
Q
Define Hox genes!
A
- These are a subset of homeobox genes, only in ANIMALS, determining the embryonic body regions along the anterior-posterior axis!
- These Hox genes are organised into groups known as Hox clusters, as each gene codes for specifica area of development
- Vertebrates have four Hox clusters, which are found on different chromosomes
- Linear order present in Hox genes , this order is directly related to the order of the regions of the body that they affect!!
23
Q
How exactly does apoptosis occur?
A
- Enzymes break down cytoskeleton, as cytoplasm becomes dense with tightly packed organelles
- cell surface membranes form protusions (blebs)
- chromosome condensation, DNA and nuclear envelope breaks down
- Cell breaks down into vesicles, where phagocytes engulf + digest cells…
24
Q
Control and Importance of Mitosis and Apoptosis??
with NAMED EXAMPLES!!
A
- Homeotic genes control rate of apoptosis/mitosis
- Constantly producing + destroying cells at controlled rate throughout the early development!
the presence of pathogens - Examples = limb separation / organ growth in Embryos / Removal of T lymphocytes that may recognise self-cell antigens as foriegn / Tadpoles loosing tail during adolescence….
