Gene Expression and Stem Cells Revision

PROTO-ONCOGENES encode proteins that STIMULATE cell division mutation = oncogene makes too much active protein all the time cell divides unchecked - can lead to cancer mutation is DOMINANT

TUMOUR - SUPPRESSOR GENES encode protein that INHIBIT cell division mutation = stop protein made so cell can pass through checkpoints mutation is recessive - both copies of gene must mutate

OESTROGEN hormone that can affect transcription binds to a transcription factor called receptor complex complex moves from cytoplasm - nucleus it binds to specific DNA site near start of gene complex either acts as an ACTIVATOR - helping RNA polymerase. or acts as a (REPRESSOR - blocking RNA polymerase this depends on type of cell) level of oestrogen affects rate of transcription of genes

RNA polymerase attaches to DNA double helix at start of gene hydrogen bonds broken so DNA uncoils one strand is then used as a template to make mRNA copy RNA lines up free RNA nucleotides along template. specific base pairing - mRNA is complementary copy of DNA nucleotides paired with specific bases on DNA - joined together forming mRNA RNA polymerase moves along - separating DNA and assembling mRNA hydrogen bonds reform on DNA once RNA polymerase has passed - strand recoils into double helix when RNA polymerase reaches stop codon - stops making mRNA and detached from DNA mRNA is then edited

EDITING mRNA eukaryotic DNA contain section that dont code for amino acids - INTRONS bits needed - EXONS during transcription both are copied to mRNA from DNA - this forms pre-mRNA introns removed from pre-mRNA - SPLICING exons joined together forming mRNA mRNA then leaves nucleus onto ribosome in cytoplasm

mRNA attaches to ribosome and tRNA carries amino acids  to ribosome tRNA with complementary anticodon to first codon on mRNA attaches to mRNA by specific base pairing 2nd tRNA molecule attaches to mRNA in the same way 2 amino acids attached to tRNA are joined by peptide bond. 1st tRNA molecule moves away leaving amino acid behind 3rd tRNA molecule binds to next codon behind the 2nd. its amino acid binds to the first 2 and the 2nd tRNA moves off process continues producing a polypeptide chain until it reaches a stop codon on mRNA polypeptide chain moves away from ribosome.

STEM CELLS TOTIPOTENT STEM CELLS = can develop into a complete organism. found in embryos up to the 32 cells stage PLURIPOTENT STEM CELLS = can differentiate into nearly all cells. found in blastocysts (5 day old embryo - 150 cells) - embyronic stem cells MULTIPOTENT STEM CELLS = can differentiate into related family cells. found in some tissues throughout life. - adult stem cells - used in body to replace and repair damaged tissue

DELETION AND INSERTION MUTATION cause frame shift may not change the actual sequence of bases. all amino acids after the mutation are shifted left or right so protein is completely wrong and non functional

SUBSTITUTION MUTATION NONSENSE MUTATION = base change resulting in the formation of a STOP CODON - may result in shorter polypeptide chain thus changing primary structure. MIS-SENSE MUTATION = base change resulting in different amino acid coded for SILENT MUTATION = base change dpesnt result in different amino acid - may be more than one triplet coding for the same amino acid - DNA code is DEGENERATE

cancer and oestrogen

transcription

editing mRNA and mutations

translation

stem cells