6.1.1 Cellular Control COMPLETE Flashcards
DEFINITION- Mutation
A random mistake that causes a change in the structure of DNA, or the structure/ number of chromosomes.
Occur when DNA is replicating prior to mitosis or meiosis.
They’re spontaneous but rate is increased by mutagens such as radiation.
Types of Mutation
Substitution
Deletion
Insertion
Substitution
Swapping one or more base for another base, this causes a change in one triplet and may change the amino acid
Deletion
The loss of one or more base causing a frame shift, all the following base triplets are disrupted
Insertion
The addition of a new base/ bases which also causes frame shift
Effects of mutation
- No effect
- Harmful Missense mutation
- Harmful Nonsense mutation
- Beneficial mutation
No effect mutations
Single base mutations often have no effect because the DNA code is degenerate
A mutation may also code for a different amino acid which is chemically similar to the original amino acid and away from an active site meaning theres not functional effect
Missense Mutation- Harmful
A change in the amino acid may lead it to becoming less effective or not function at all, this decreases chance of survival likelihood.
A single change in the amino acid may affect the tertiary structure meaning the active site is no longer complementary to the substrate
Nonsense Mutation- Harmful
Mutations may cause a stop codon to be introduced part way along the gene, leads to a short non functioning polypeptide.
May mean that RNA polymerase is unable to bind properly meaning transcription can’t take place
Beneficial Mutation
Occasionally a change in the amino acid in protein can lead to it being more effective, increasing the chance of survival.
i.e. antibiotic resistant bacteria
Somatic Mutation
Not inherited but can cause ageing and cancer, result of mutation in normal diploid cells
Germline Mutation
Due to mutation during gamete formation, can cause genetic diseases and are passed onto the next generation.
When beneficial it begins about evolution
Gene Expression
Different genes are switched on and off in different cells so that they’re specialised to perform different functions and not make proteins we don’t want.
Transcriptional Level Regulation of Gene Expression
To produce a protein a gene is transcribed into mRNA, the RNA polymerase must bind to the DNA near the start of the gene called the promotor.
DEFINITION- Operon
Structural genes that code for proteins that work together, are sometimes found in groups together with a single promoter.
The Lac Operon
- Collection of genes responsible for lactose digestion and their regulation.
- If glucose is unavailable the E.Coli can also absorb and hydrolyse lactose.
- To save resources it only produces the enzymes needed when lactose is available
- When Lactose is present both Lactose Permease and Beta Galactosidase
Lactose Permease
Transports lactose into the cell acting as a carrier protein
Beta Galactosidase
Hydrolyses Lactose into glucose and galactose
Process when no lactose is available
Lac Operon
- Regulator gene transcribes mRNA which translates a repressor protein
- Repressor protein binds to operator site and blocks the transcription of structural genes
- RNA polymerase cannot bind to the promotor region which blocks the transcription of Lactose Permease and Beta Galactosidase
Process when lactose is available
Lac Operon
- Regulator gene transcribes and translates a repressor protein
- Lactose binds to the allosteric site so it no longer bins to the operator site
- RNA polymerase can therefore bind properly to the promotor region
- Beta Galactosidase and Lactose Permease can be transcribed and translated
Transcriptional Level Regulation of Gene Expression in Eukaryotes
In eukaryotes, proteins or non coding pieces of RNA called Transcription Factors can bind to the DNA at promotor regions.
These either allow RNA polymerase to bind (Activators)
or prevent them binding (Repressors)
When DNA is tightly wound around histone proteins during mitosis or meiosis, it is not able to be used for protein synthesis.
Post transcriptional Level control
Eukaryote genes contain Exons and Introns
Primary mRNA must be edited in the nucleus to remove the introns, this produces mature mRNA corresponding to DNA exons
Endonuclease enzymes must be used
Introns
Post transcriptional level Control
Non coding DNA within genes
Interruptions
Exons
Post transcriptional level Control
DNA that codes for amino acids
Expressed
Post Translational Level Control
Proteins that have been transcribed and translated may need to be activated.
This could be modification in the Golgi apparatus, e.g. add carbohydrate
Many enzymes need to be phosphorylated which alters the charge, tertiary structure and hence function.
Catalysed by Protein kinases, may need to activated by cyclic AMP
Homeobox Genes
- Control the development of a zygote to a complete organism
- The genes switch a whole set of other genes on or off affecting the organisms overall body plan
- Code for the production of transcription factors which can bind to certain sections of DNA causing it to be transcribed
- Very little mutation across species
DEFINITION- Hox Genes
Homeobox genes found only in animals, responsible for the correct positioning of body parts, thalidomide disrupted this
Maternal Effect Genes
Determines the embryo polarity, which end will be the head and which will be the tail
Segmentation Genes
Specify the polarity of each segment
DEFINITION- Apoptosis
Programmed cell death
e.g. the tail of a tadpole
Process of Apoptosis
- Cell receives internal and external signals including cytokines, hormones ect.
- Cytoskeleton broken down by enzymes, cell shrinks and membrane blebs
- Nucleus begins to disintegrate, chromatin condenses and DNA breaks down into fragments
- Cell fragments made with intact plasma membranes containing organelles
- Cell fragments are ingested and digested by phagocytic cells
Problems linked to apoptosis
- Not enough leads to the formation of tumours
- Too much leads to degeneration of tissue
- Cell signalling usually monitors the correct balance
