Wk. 3 | Transcription and Translation Flashcards
What is transcription?
The transfer of information from DNA to RNA
Simplified version of the central dogma
DNA -> transcription -> RNA -> translation -> protein
What is the role mRNA
carries genetic info to the entire cell
Process of Transcription
- DNA strands are pulled apart
- A single strand of RNA molecule is made using the antisense DNA strand as a template.
- This strand is complementary to the DNA except T replaced with U - RNA is synthesized 5’ to 3’
Which direction is RNA synthesized in transcription
5’ to 3’
The product of transcription is
mRNA
Transcription occurs when
only when specific gene needed
The enzyme that makes RNA in transcription
RNA polymerase
RNA Polymerase Function
binds to DNA at the start of a gene and opens the double helix
makes RNA from the antisense strand of DNA
The _____ strand is the DNA strand transcribed to make mRNA
antisense
The coding or sense strand is
the complementary strand of DNA
What recognizes the promoter?
the sigma subunit of RNA polymerase
The ___________ strand matches the mRNA strand that was just synthesized
coding/sense strand
The sigma subunit of RNA polymerase recognizes what two sequences
-10 and -35 regions on the opposite DNA strand
-10 sequence codes for what
TATA box in eukaryotes
- TATAAT
-35 region sequence
TTGACA
Upstream region of DNA
stretch of DNA in front of a gene
Where does RNA polymerase bind?
the promotor region
Consensus Sequence
- can be ____________
- __________________ depends on how closely it matches consensus sequence
one or two bases off and sigma subunit will still recognize
Strength of a promotor
What is located upstream and downstream?
Upstream: promotor
Downstream: gene
Once the sigma subunit has been found…
a promotor + RNA polymerase binds
sigma subunit drops off, remaining portion is the core enzyme
2 ways transcription is terminated in prokaryotes
Rho-independent
Rho-dependent
Rho Independent
- A ______________________ tells ____________ where to stop
- Termination sequence consists of _______ separated by ~ _ bases followed by numerous ___
- The two _______ are on opposite strands of DNA
- terminator sequence, RNA polymerase
- 2 inverted repeats, 6, As
- inverted repeats
Rho-independent | Inverted repeats on the same strand of RNA pair up to form a
hairpin loop followed by a run of U’s
Rho Dependent
- A protein factor Rho does this
destabilizes the interaction between template and mRNA, releasing the mRNA
Termination in Eukaryotes
- New transcript is ____________
- Followed by _____________ of the __ end
- cleaved
- polyadenylation, 3’
Genes that are on all the time
- constitutively expressed
- housekeeping genes
These types of genes have -10 and -35 regions IDENTICAL to consensus and are ALWAYS
- housekeeping genes that are on all the time
- recognized by sigma
Genes that are only needed under certain conditions have ________ are not recognized without _______
poor recognition sequences
accessory proteins
Gene activator proteins are a type of gene that is
only needed under certain conditions
Gene activator proteins
helps the RNA polymerase bind to the DNA
aka transcription factors
What do repressor proteins do? (3 things)
- turn off genes
- bind DNA and block action of RNA polymerase
- bind to the operator sequence
Does RNA polymerase or activator protein bind to DNA first?
activator protein, then RNA polymerase
“help yourself before helping others put their mask on”
How do regulators work?
Fits into the binding site on regulatory protein -> signal molecule changes shape (allosteric)
What is global regulation
the coordinated control of large groups of genes
What is an operon
a group of genes that all have the same promotor and are regulated together
Operons are found in
prokaryotes
Antisense RNA is
RNA that is complementary to the mRNA and can base pairs with it
If you make an RNA from the non-template strand, you would produce an RNA molecule that’s
complementary to the mRNA
Function of antisense RNA
blocks translation by preventing mRNA binding to the ribosome by base pairing with the complementary mRNA
Prokaryote vs Eukaryote Transcription
Prokaryote
- Occurs in _________
- mRNA is usually __________
- Cytoplasm alongside translation
- NOT modified
Prokaryote vs Eukaryote Transcription
Eukaryote
- Location: _____________
- DNA access controlled by
- mRNA ___________ through RNA splicing, 5’ end capping, and polyA tail
- localized in nucleus, transcript is transported to cytoplasm where translation occurs
- chromatin
- modified
Polyadenylation
- _________ nucleotides added to the __ end of mRNA by ______________
- Typical run is ___ nucleotides
- adenine
- 3’
- polyadenylate polymerase
- 200
The polyA tail is _______ in genomic DNA
not coded
5’ Capping
- Addition of ________ _________ to the 5’ end of mRNA.
- Function:
methyl guanosine
- protective, acts as a recognition signal
The 5’ cap is made of a
5’ - 5’ pyrophosphate bridge to a methylated guanosine
Prokaryotic genes are
uninterrupted open reading frames
What happens during splicing
Eukaryotic coding sequences separated by introns
Introns are removed by splicing
Only exons (able to code for proteins) remain
Exons
Eukaryotic sequences that code for proteins
Introns
long stretches of non-coding sequence that separate exons
Does mRNA perform any work?
NO, it is just a message
There are __ amino acids total
20
Aminos consist of a central hydrocarbon surrounded by:
- NH2 (amino group)
- COOH (carboxyl) group
- A variable group (side chain)
______ bonds join amino acids
peptide
4 Roles of proteins
- Structural proteins: flagella, microtubules, etc
- Enzymes: carries out chemical rxns
- Regulatory proteins
- Transport proteins
Regulatory Proteins
A protein that controls expression of a gene or activity of another protein
Transport Proteins
A protein that carries other molecules across membranes or around the body
Amino terminus
amino (NH2) group at the end of the first amino in the chain
Carboxyl terminus
carboxy (COOH) group at the end of the last amino in the chain
A complete protein can have ______ polypeptide chain
a.) only one
b.) more than one
more than one
Cofactors are or are not made up of amino acids
NOT
Primary Structure
The sequence/order of monomers
Secondary Structure
The folding of the original polymer chains thru H bonding
Tertiary Structure
- 3D folding
- Result of hydrophobic inner and hydrophilic outer groups
Quaternary Structure
Assembly of several individual polypeptide chains to give final structure
Ribosomes bind to ____ and do what
bind to the 5’ end of mRNA and translates it
After binding, the ribosome
moves along the mRNA adding a new amino each time it reads a codon
Translation Rule
In general, 1 gene codes for 1 protein
Adaptor Molecules
Transfer RNA, carries amino to ribosome
Codon and anti-codon pairing
tRNA has a
- an anticodon at one end
(3 bases complementary to the mRNA)
Wobble Rule
- Allows tRNA to ________
- Less rigid _________ for __________ pairing so
- _____ tRNA base can wobble around
- recognize different codons
- base pairing
- codon/anticodon
- First
Each tRNA carries _______
- a single amino acid
There are __ codons to be recognized
64
For each tRNA there is an enzyme that
recognizes the tRNA and the corresponding amino acid
What charges tRNA
amino-acyl tRNA synthetase
What is a charged tRNA?
tRNA with its amino attached
What is the structure of tRNA?
Cloverleaf
4 short base-paired stems + 3 loops
Where is the amino acid bound on tRNA?
the free acceptor stem (on the opposite end of the anticodon
The other two ends of the tRNA are needed for
- binding to the ribosome
- recognizing the adaptor enzyme
What is a reading frame?
one of 3 possible ways to read the bases of mRNA in groups of 3 to give codons
Start Codon(s)
AUG - methionine
What is an open reading frame?
What is translated into a protein!
A stretch of RNA beginning with a start codon that can be translated into protein
How many open reading frames per mRNA are there
several
An initiator tRNA is
charged and chemically tagged with methionine
- Formyl-methionine (fMet)
fMet binds to the
start codon
Proteins are made from a linear chain of
monomers (aminos)
________ allows proteins to carry out their function. This must be done correctly
Folding
Amino acids have a central hydrocarbon atom surrounded by
- NH2 amino group
- COOH carboxyl group
- R or variable group
Stop Codons
- UAG
- UGA
- UAA
Each protein is made using
the genetic info stored on the chromosomes
Shine-Delgarno sequence is the
site of initiation in prokaryotes
- includes ribo binding site, spacer, and AUG
Kozak Sequence
helps the ribosome identify the start codon in eukaryotes
Initiation
1. mRNA binds to ______________________
2. ________________ recognizes AUG start
3. __ ____________________ help arrange all components
4. _____ ribosome subunit arrives and the ______________ fall off
- small subunit of ribosome
- Initiator tRNA w/ fMet
- 3 initiation factor proteins
- Large; initiation factors
Ribosome sites for tRNA in elongation
A-site: acceptor site
P-site: peptide site
Elongation
1. fMet initiator tRNA starts at the ______
2. Another tRNA carrying next amino enters the _____
3. fMet is cut loose and bonded to _______
4. tRNA number 2 now carries _______________
- P-site
- A-site
- Amino number 2
- 2 linked amino acids
Elongation factors do what
supervise shifting of tRNAs on the ribosome
EF-T function
delivers tRNA to ribosome and installs it into the A-site
EF-T is made of these two elongation factors
EF-Tu
EF-Ts
Function of EF-G
oversees that everything moves sideways at the correct time
Termination
1. Stop codon reaches the _____________________
2. _____________ chop completed polypeptide chain from tRNA
3. Ribosome falls off and __________________
- A site of the ribosome
- Release factors
- separates into its subunits
Polysome
complex formed when multiple ribosomes are translating the same mRNA into proteins
DNA is made in the 5’ to 3’ direction by adding nucleotides to the __ end
3’
