5584804
Description
Mind Map by Natalina Laria, updated more than 1 year ago
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Created by Natalina Laria
over 8 years ago
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Gene structure, expression and
regulation in prokaryotes
- Bacterial genome
- Circular chromosomal DNA
- Typically a few million base pairs
long
- Most bacterial species contain a
single type of chromosome
- A few thousand different genes
are interspersed throughout the
chromosome, genes separated by
short, intergenic regions
- One origin of replication is
required to initiate DNA replication
- No nucleus
- Haploid (one copy of every gene)
- Small compact
and repetitive
- Circular chromosomal DNA
- Plasmids
- Replicate independently
- Can integrate into chromosome
- Not essential for survival
- Fewer genes
- Replicate independently
- Gene organisation in Prokaryotes
- Organised into operons
- A set of genes encoding proteins
participating in the same metabolic
pathway
- A set of genes encoding proteins
participating in the same metabolic
pathway
- Transcribed as polycistronic mRNA
- Several proteins under influence of
one promoter
- Advantage:
timing and
amounts
- Disadvantage:
mutations
inflexible
- Advantage:
timing and
amounts
- Several proteins under influence of
one promoter
- Organised into operons
- Transcription
and translation
- Occur at the same time
in the “same cellular
compartment”
- Translation of an mRNA may
begin before the mRNA is
completely transcribed
- Transcription unit
- Promoter
- Important in
initiation
- Conserved sequence of nucleotides in a
DNA strand that is a binding site for
RNA polymerase
- Position and orientation of
the promoter determines
which strand is transcribed
and where transcription
starts
- Important in
initiation
- RNA coding
region
- Terminator
- Promoter
- Transcription
- Copying of template DNA strands
- Strands
grow in a
5' to 3'
direction
- RNA
polymerases can
initiate strand
growth
- DNA
polymerases
require a
primer
- Occurs in 3 phases
- Initiation
- Sigma factors recognise the
promoter to initiate
transcription
- Promoter recognition
Formation of
transcription bubble
Creation of bonds
between rNTPs Escape
from transcription
apparatus from
promoter
- Sigma factors recognise the
promoter to initiate
transcription
- Elongation
- Termination
- Rho-independent
Characterised by
1.) inverted
repeats 2.) string
of adenines ->
slow down
polymerase ->
formation of
hairpin structure
followed by a
string of uracils
- Rho-dependent 1.)
DNA region, that
slows polymerase
down 2.)
Unstructured
region -> binding
site for rho
protein, catches
up, helicase
activity
- NO
HAIRPIN
STRUCTURE
- NO
HAIRPIN
STRUCTURE
- Rho-independent
Characterised by
1.) inverted
repeats 2.) string
of adenines ->
slow down
polymerase ->
formation of
hairpin structure
followed by a
string of uracils
- Initiation
- Copying of template DNA strands
- Translation
- Genetic code is read in
triplicate but can be read in
different frames
- Genetic code
and mutations
- Silent mutation: the
base change does not
result in a protein
change
- Mis-sense mutation: a
single amino acid is
changed
- Nonsense mutation: an
amino acid codon is
changed to a stop codon
- Frameshift mutation:
insertion or deletion of a
number of nucleotides that
is not a multiple of three
- Silent mutation: the
base change does not
result in a protein
change
- Genetic code
and mutations
- Different phases
- Charging of tRNA
- Amino
acid links
to tRNA
- tRNA then binds its codon in RNA
- Net result = amino acid is selected for by its codon
- Net result = amino acid is selected for by its codon
- tRNA then binds its codon in RNA
- Amino
acid links
to tRNA
- Initiation
- Requires
ribosomes
and initiation
factors
- Complementary base-pairing between the
Shine-Dalgarno sequence on the mRNA and
the rRNA occurs
- Small subunit binds to
Shine-Dalgarnonsequence with the help
of IF3
- Then fMet-tRNA binds to initiation
codon with the help of IF1, IF2 and
GTP
- This is called the 30s initiation complex
- Then IFs are removed and large subunit is added
- This is called the 70s initiation complex
- In summary the ribosome has been assembled on the
mRNA and the first tRNA is attached to the initiation codon
- In summary the ribosome has been assembled on the
mRNA and the first tRNA is attached to the initiation codon
- This is called the 70s initiation complex
- Then IFs are removed and large subunit is added
- This is called the 30s initiation complex
- Then fMet-tRNA binds to initiation
codon with the help of IF1, IF2 and
GTP
- Complementary base-pairing between the
Shine-Dalgarno sequence on the mRNA and
the rRNA occurs
- Requires
ribosomes
and initiation
factors
- Elongation
- Termination
- Once ribosome
reaches stop codon
RFs are recruted
- Once ribosome
reaches stop codon
RFs are recruted
- Charging of tRNA
- Genetic code is read in
triplicate but can be read in
different frames
- Occur at the same time
in the “same cellular
compartment”
- Types of RNA found in prokaryotes
- mRNA
- tRNA
- rRNA
- mRNA
- Lac operon
- lacZ
- b-galactosiadase
- Splits lactose into
galactose and
glucose
- Splits lactose into
galactose and
glucose
- b-galactosiadase
- lacY
- Lactose permease
- Transports lactose into cell
- Transports lactose into cell
- Lactose permease
- lacZ
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