Week 8 - Gene expression

Question 1

gene expression

Answer 1

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

Question 2

gene regulation

Answer 2

• 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

Question 3

turning genes on & off

Answer 3

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

Question 4

gene expression - control

Answer 4

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

Question 5

Transcriptional regulation - bacteria

Answer 5

• 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.

Question 6

gene regulation - prokaryotes

Answer 6

• 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

Question 7

gene expression - prokaryotes

Answer 7

• 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

Question 8

eukaryotic regulation

Answer 8

• 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

Question 9

transcription factors

Answer 9

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

Question 10

gene expression - importance

Answer 10

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

Question 11

enhancers

Answer 11

• 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

Question 12

gene regulatory cascades - eukaryotes

Answer 12

• 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

Question 13

Key points

Answer 13

• 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.