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Flashcards in Week 8 - Gene expression Deck (13)
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gene expression

- how information in genes is used to produce proteins, functional RNAs


gene regulation

- refers to the ability of cells to control their level of gene expression
- majority of genes are regulated so proteins are produced at certain times in specific amounts


turning genes on & off

1. cells respond to changes in the internal & external environment by turning genes on & off , cONSERVES energy & resources - proteins produced only when needed → helps to balance all diff processes in cells

2. Cells in a multicellular organism become highly SPECIALISED w/ specific structures & functions → have different sets of proteins and/ or differing amount of same type of protein


gene expression - control

- often accomplished by controlling: TRANSCRIPTION , INITIATION
- REGULATORY PROTEINS bind DNA to either BLOCK or STIMULATE TRANSCRIPTION, depending on how they interact w/ RNA polymerase


Transcriptional regulation - bacteria

- involves regulatory TRANSCRIPTION FACTORS ( act as on& off)
- bind to DNA in vicinity of a promoter & affect transcription of one or mroe near by genes

repressors →inhibit transcription NEGATIVE CONT
activators → inc. rate of transcription POSITIVE CONT.


gene regulation - prokaryotes

- often has to respond to changes in environment
- when lactose is not present, E.coi DOES NOT MAKE MUCH lactose permease (lactose transporter) or Beta-galactosidase (catabolism of lactose)
- when lactose available → lactose made
- when lactose levels drop → proteins are no longer made at such a high level


gene expression - prokaryotes

- prokaryotic genes are located in FUNCTIONAL GROUPS (OPERONS) allows certain genes to be controlled together
- genes encoding enzymes in same pathway are arranged in sequence under control of a SINGLE PROMOTER


eukaryotic regulation

- control is more complex
- major diff from prokaryotes
→ eukaryotes have DNA organised into chromatin: complicates protein DNA interation
→ eukaryotic transcription occurs in nucleus
- amount of DNA involved in regulating eukaryotic genes much higher


transcription factors

General factors:
- necessary for the assembly of a transcription apparatus and recruitment of RNA polymerase II to a promoter & initiate transcription
- they required for transcription → do not inc. transcription above basal rate
- TFIID recognises TATA box sequence

Specific factors:
- inc. level of transcription in certain cell types or in response to signals


gene expression - importance

- cellular differentiation
- respond to environment
- save resources
- maintain constant intracellular conditions



- promoters from the binding site or gen. transcript factors
- enhancers are the binding sites of the specific transcription factors
- DNA bends to form loop to position enhancer close to promoter
- diff enhancers are associated w/ diff genes
- enhancers function in positive control
- when regulatory proteins bind to enhancers, transcription begins


gene regulatory cascades - eukaryotes

- transcription factors bind to ENHANCER/ SILENCER sequences → are gene products
- coordinated expression of many genes can therefore be achieved by just a few genes
- often tissue specific allowing a complex pattern of gene expression
- such regulatory cascades are important in embryonic development of eukaryotes


Key points

- gene expression affects the amount of functional RNA & proteins produced in a cell
- gene expression is controlled
- genes may be expressed constantly or differentially regulated
- changes in gene expression allow eukaryotic cells to respond to changes in the environment & cause distinct cell types to develop
- in eukaryotes, transcrip. initiated only when proteins in factors bind to promoter & reg seq.