6.1.1 Cellular Control Flashcards
Mutation
Change in the base sequence of the DNA in a gene
Randomly occur during DNA replication
Substitution
Base substitution may be ‘silent’ - new codon still codes for the same amino acid
Genetic code is degenerate (multiple codons code for the same amino acid)
Base deletion/insertion
Base inserted or deleted from sequence
Results in a frameshift & codes for different amino acids > protein
Effects of gene mutations
Result in different amino acid sequence > different folding + coiling > different hydrogen + ionic bonds - results in a different 3D shape
Not all mutations are harmful, can be beneficial (antibiotic resistance in bacteria) or can be neutral
Transcription factors
- Transcription occurs when a molecule from the cytoplasm enters the nucleus & binds to the DNA in the nucleus
- The molecules are proteins (transcription factors) each one can bind to different base sequences on DNA > initiate transcription of genes
- Can turn on/off genes
- When bound, transcription begins - creates mRNA molecule for that gene which cane be translated in the cytoplasm to create the protein
- Gene is inactive before binding
Lac operon overview
- Group of simultaneously controlled genes that are all expressed or not
- If glucose not present, lactose will be digested
- Proteins produced by the lac operon are needed if glucose is absent + lactose is present
Lac operon structure & function
- Contains 3 genes: lacZ, lacY, lacA
- LacI is a regulatory gene found near the operon - codes for a repressor protein which inhibits transcription when no lactose
- No lactose - repressor protein constantly produced, binds to operator which prevents RNA polymerase from binding at promoter region - inhibits transcription
- Lactose is present - binds to repressor protein, changes shape - prevents it from binding to operator - RNA polymerase can bind to promotor > transcription occurs
- cAMP increases rate of transcription, CRP binds as well once bound to cAMP
Post-transcriptional changes
mRNA modification:
-pre-mRNA before synthesis
- Removal of all introns by spliceosome (splicing)
- Rearrangement of exons
Post-translational changes
- Non-protein groups assed in Golgi
- Proteins folded to unique 3D shapes
- Some proteins made inactive > activated by phosphorylation
Homeobox genes
Sequences of genes which create proteins that regulate the expression of other genes involved in formation of the body as an embryo
Highly conserved in plants, animals, fungi
Hox genes
- Type of homeobox gene in animals
- Responsible for the correct body development + positioning of body parts
- Regulate mitosis & apoptosis
- Order of the genes in DNA same in which their effects are expressed in the organism
- Body development of most organisms shows symmetry
Mitosis & Apoptosis
Mitosis: results in an increase in number of cells - growth
Apoptosis: (programmed cell death) - removes unwanted cells
- New cells only made when needed for growth + repair to preserve energy & prevent tumour formation
- If error detected/too old to function, apoptosis occurs + resources recycled
