cellular control Flashcards
what is nonsense
- mutation results in one of the three stop codons
what is missense
results in different amino acid sequence being coded for
what is silent
different codon
same amino acid is coded for
what is insertion
addition of a nucleotide
what is deletion
nucleotide removed
what is frame shift
causes all further amino acids to be changed including start and stop codons
what are the effects of mutations
Neutral - normal functioning proteins synthesised - phenotype unchanged
Harmful = proteins not synthesised and not functional - phenotype negatively impacted
Beneficial = protein synthesised with a new and useful characteristic in phenotype
what are the causes of mutations
- occur naturally and spontaneously during DNA replication but appearnace increased by mutagens
- x-rays, high energy radiation, chemicals in cigarettes
how is a gene switched off
- site on the transcription factor binds to DNA and is blocked by an inhibitor
- prevents transcription
how are genes turned on
- hormones activate transcription factors
what are transcription factors
- proteins move in from the cytoplasm and bind to DNA at the start of target genes
- activators
- repressors
how do transcription factors control gene expression at the transcriptional level
- altering rate of transcription of genes
- controlled by transcription factors
- shape of a transcription factors determines whether it can bind to DNA or not
what are the features of a operon
- structural gene codes for useful proteins
- control elements = promotor (RNA polymerase binds) and operator (transcription factor binds to)
- regulatory gene - codes for activator or repressor
the lac operon in E.Coli
- E.Coli respires glucose but can use lactose
Lactose not present
- regulatory gene produces lac repressor
- transcription factor that binds to operator site when there is no lactose
- blocks transcription as RNA polymerase cannot bind
Lactose Present
- lactose binds to repressor
- repressor shapes changed and no longer binds to operator site
- RNA polymerase begins transcription of structural genes
how is mRNA edited at the post-transcription level
- introns and exons copied into mRNA called pre-mRNA
- introns removed from primary mRNA by splicing by a spliceosome
- introns removed and exons joined forming mature mRNA and left in nucleus
- mature mRNA leaves nucleus for translation
how does CAMP activate proteins at the post-translational level
- protein activation is controlled by hormones and sugars
- molecules work by binding to cell membranes and triggering production of CAMP inside the cell
- CAMP activates proteins inside the cell by altering the 3D structure
PKA is an enzyme made of 4 sub-units
when CAMP isn’t bound the four units are bound together and inactive
what are body plans
general structure of an organism
what are homeobox genes
- sequence of 180 base pairs found within genes in regulating anatomical development in plants, animals, fungi
what are hox genes
- subset of homeobox genes
- involved in formation of anatomical features of an animal
homeodomain proteins
- coded for by hox genes
- act as transcription factors to activate, repress genes, regulate mitosis, apoptosis and the cell cycle
how do hox genes control development
- homeobox sequences code for homeodomain proteins
- homeodomain binds to specific sites on DNA enabling protein to work as a transcription factor
- proteins bind to DNA at the start of developmental genes, activating or repressing transcription
- alter the production of proteins
what is apoptosis
- programmed cell death
- series of biochemical events leading to orderly cell death
- too much = cell loss
- too little = tumours
what are the events of apoptosis
- enzymes inside the cell breakdown important cell components such as proteins and DNA
- cell contents begin to break up and shrink into fragments
- fragments engulfed by pathogens and digested
how is apoptosis controlled
- regulated by hox genes
Internal
- damage to DNA detected in the cell cycle
- genes expressed that cause the cycle to stop
- release of hormones
External
- change in light intensity or temperature
- pathogen attack
- lack of nutrients
- drugs = thalidomide
