BIS 101 lecture 2: Transcription

define Gene

sequence of DNA at a specific location in the genome that encodes information

to direct the synthesis of a biological end product (biomolecule)

such as a protein or RNA.

a gene is the P…. and F….. U….. of H….

a gene is the Physical and Functional unit of Hereditary

define genome

the complete set of DNA, (including all of its genes), in a cell/ organism/ species

what is a genotype

the different variations of genes that an individual possesses for a particular trait.

what is the phenotype

observable and measureable traits and behaviours

what is gene expression?

the cellular production of biological molecules

driven by the information encoded in the DNA sequence

how does genotype → phenotype

via gene expression

what is transcription?

process of reading a single strand of DNA template and building an RNA molecule based off the DNA template

3 steps of transcription?

1. initiation: specific proteins recognise a gene to start transcription

2. elongation: synthesising the RNA transcript

3. Termination: RNA synthesis stopped and RNA is released

what is a promoter?

where is it found?

Why is it important?

• a promoter is a DNA sequence found upstream o0f the transcription start site of a gene

• it is required to begin the transcription of a gene

• the promoter sequence is recognised by a protein which binds to it. the protein initiates transcription

what portion of the DNA is in the mRNA

only the transcribed region

where is the transcription start site?

the +1 site on the DNA strand is where transcription begins

• it is the first base in the mRNA

what are the promoters in prokaryotes

what binds to the promoters

the -35 box and the -10 box

sigma factors bind to the promoters

how is transcription initiated in prokaryotes?

1. the sigma factor binds to the -35 and -10 box simultaneously.

2. the RNA polymerase core enzyme attaches to the sigma factor

This forms RNA polymerase hollow enzyme

1. RNA polymerase hollow enzyme begins transcribing → forms RNA

why doesnt the RNA polymerase core enzyme just bind to the promoter sequence?

it has poor promoter binding

how does the prokaryote’s machienary know which genes to transcribe

1. there are multiple sigma factors which match the promoter sequence

2. each sigma factor has a slightly different version of the 35 10 consensus

3. only when the sigma factor which matches the 35 10 promotor, the gene is transcribed

the cell regulates the sigma factors that are present

what is the main sigma factor in prokaryotes?

sigma 70

• it is used for most prokaryote genes including housekeeping genes: genes that are continuously on

local impact vs global impact

local impact: affects expression of only the mutated gene

global impact: affects many genes at the same time

which directions does RNA polymerase work in

• it synthesises in the 5’ to 3’ direction (5’ phosphate group is attached to the 3’ -OH group on the previous nucleotide.)

• it reads in the 3’ to 5’ direction.

which direction do the RNA, template and coding strands go in?

are they complementary and parallel nature relative to the RNA strand

RNA strand: 5’ to 3’

coding strand: 5’ to 3’ → identical to RNA strand (except T instead of U) → non-complementary and parallel to RNA strand

template strand: 3’ to 5’ _> antiparallel and complementary to RNA strand

what are the major themes for termination?

what are the 2 major theories for termination?

• there is a terminator sequence in the DNA

• it signals for the RNA polymerase to detach and stop synthesis

• it is transcribed into the RNA which catalyses termination

theories:

a) a protein binds to the terminator sequence on RNA → RNA polymerase detaches

b) the terminator sequence on RNA folds on itself → RNA polymerase detaches