Module 6: cellular control ,patterns of inheritance

Question 1

Mutations : definition , types , effects

Answer 1

Mutation - change in DNA base sequence caused by mutagens

• point mutations ( effects only 1 base -nucleotide) - e.g. substitution (base change to another base) , insertion (extra nucleotide in one place ), deletion (removing base from sequence)
• frame shift - cause of insertion /deletion of a base , disrupt triplet code reading (codon) - diff protein is made

Effects - natural/silent - no effect ( degenerate nature codon)
- Beneficial- enchanted function protein
- damaging - e.g. cancer , malfunctioning protein

Other mutations :nonsense ( codon has changed to stop codon -premature ) , misense (amino acid changed -degenerate coding failed )
-duplication , inversion, translocation ( section big moved )

Question 2

Levels control of gene expressions

Answer 2

4 levels of control :
- Transcriptional - turning genes on/off
- post -transcriptional - Editing RNA
- - Translational - turning translation on/off
- Post- translational - editing protein

Question 3

Transcriptional control of gene expression

Answer 3

• alter conditions to allow RNA polymerase to bind in eukaryotes ( histone modification for remodelling ) , prokaryotes (lac operon)
• heterochromatin ( tightly wound dna in cell division) converted to Euchromatin ( loosely wound dna in interphase ) by acetylation / phosphorylation- this decreases the +ve charge of his tones
• ## opposite direction - methylation - increases the hydrophobic nature of histones

Question 4

Lac operon - prokaryotes of transcriptional control of gene expression

Answer 4

Operon - a group of genes controlled by the same regulatory mechanism & expressed at the same time

Structural genes ( lac z,y,a ) - proteins not involved in DNA regulation
- B- galactosidese , lactose permease , transacetylese ( enzymes that metabolise lactose
Regulatory genes - proteins involved in DNA regulation - repress or protein

Interaction :
Lac I - operator - promoter - lac z - lac y - lac A
1. Where glucose is , lacI is expressed making repressed protein , bonds to operator
2. Change in size / shape - it blocks the RNA polymerase binding site on the promoter - structural gene transcription can’t occur
3. If there’s lactose instead , binds to repress or protein , conformational change , the repress or is released from operator
4. Release of the repressor from operator unblocks the binding site on the promoter - RNA polymerase binds to transcribe the structural genes

Make transcription more efficient- cAMP receptor protein bud to cyclic AMP & upregulates activity of RNA polymerase

5. Glucose decreases cAMP concentration in cell - less CRP-cAMP complexes made bind to RNA polymerase
6. Lactose is released from repressor protein binds again to Preston - prevent RNA polymerase from binding

Question 5

Post- transcriptional ( modify mRNA)

Answer 5

• DNA - transcription occurs - makes Pre- mRNA
  ( precursor) - 1. RNA splicing ( remove all the introns - don’t code for protein ) - 2. Add modified nucleotide at the front and tail of adenine - stabilises mRNA prevent degradation - 3 . mRNA editing - different versions of mRNA different proteins diff functions

Question 6

Translational and post-translational gene expression control

Answer 6

Translational - downregulate translation - 1. Degrade mRNA 2. Inhibitory proteins bond to mRNA - stop bind to ribosomes
- upregulate - 1. Activate initiation factors ( mRNA bind to ribosomes by phosphorylation- done by , protein kinases ( activate by cAMP)

Post-translational control - modifying the polypeptides to make proteins of specific functions
1. Add non-protein groups ( lipoprotein, glycoprotein )
- modify amino acids to make bonds
- protein folding (tertiary/quaternary structure)
- modification by cAMP (CAMp + CRP) /camp + kineses

Question 7

Homeobox genes

Answer 7

• Regulatory genes. ( 180bp ) - code for homeodomain ( part protein ) - control body development (position body parts ) - highly conserved in plants animals and fungi - regulate mitosis /apoptosis (respond to internal /external stimuli -stress)
• hox genes - found in animals
• exam - hox genes mutated , did body arrangement-highly conserved

Question 8

Monogenic inheritance

Answer 8

5 types -
1. Homozygous crosses e.g. BB , bb - offspring 100% heterozygous
2. Heterozygous crosses e.g. Bb , Bb - offspring - 25% homozygous dominant , 50% heterozygous , 25% homozygous recessive
- 75% dominant trait , 25% recessive trait
3.Codominance - both alleles of one gene are dominant - 3 phenotypes , e.g CR CR -red , CW CW - white , CR CW - pink
RW - wrong - epistasis (2 diff genes )

4. Multiple alleles- more than 2 sellers for 1 gene e.g. blood type ABO -I -gene symbol
5. Sex linkage - gene found on sex chromosomes - male XY - female XX - makes easier effect then women

Question 9

Dihybrid inheritance - show inheritance pattern 2 genes

Answer 9

• each gamete carries one allele of both genes ( 4 different genotypes )
  -homozygous cross YYRR x yyrr - lines out 4 for each - draw Punnett square