5 - transcription and translation Flashcards
what do the genetic instructions in DNA allow organisms to do?
it contains genetic instructions that allow organisms to grow and function.
what does DNA stand for?
DNA stands for “deoxyribonucleic acid”.
what does RNA stand for?
RNA stands for “ribonucleic acid”
what does RNA do?
RNA executes the instructions given by DNA and synthesises proteins.
is DNA or RNA a type of nucleic acid?
both
is DNA or RNA a double-stranded helix?
DNA is a double stranded helix and RNA is a single-stranded helix.
where is DNA located in the cell?
the nucleus
where is RNA located in the cell?
the nucleus and cytoplasm
what is the sugar in the DNA backbone?
deoxyribose sugar
what is the sugar in the RNA backbone?
ribose sugar
what nitrogenous bases does DNA contain?
- Adenine
- Guanine
- Cytosine
- Thymine
what nitrogenous bases does RNA contain?
- Adenine
- Guanine
- Cytosine
- Uracil
what is the main type of DNA?
B-form DNA
what are the main types of RNA?
mRNA, rRNA, tRNA
what is DNA replication?
the process by which two identical DNA molecules are produced from a single original DNA molecule.
what is transcription?
the process of copying genetic information carried on DNA sequence into RNA
what is translation?
the process of converting an mRNA sequence into a polypeptide that can fold into a protein.
what are genes?
a code of instructions used to make proteins.
what is gene expression?
when a protein is produced
what is a genome?
a complete set of DNA including all the genes
what are the large stretched of DNA which do not code for proteins called?
non coding DNA and includes introns.
what is the principal role of DNA in the cell?
long-term storage of hereditary information that is necessary to build and maintain an organism.
what are codons?
protein coding information in DNA, which will be copied to mRNA, is stored via codons of 3 nucleotides.
what direction are codons read?
in a 5’ to 3’ direction
what does each codon code for?
a single amino acid
e.g. GGC-glycine
how many amino acids are there?
20
how can one amino acid have more than one codon?
the code is degenerate.
what happens from transcription to translation?
an RNA strand known as messenger RNA copies the information from the DNA strand.
in prokaryotes when does transcription and translation occur?
in prokaryotes transcription and translation can occur at the same time.
where does transcription and translation occur in eukaryotes?
transcription occurs in the nucleus and the mRNA strand travels to the cytoplasm to be translated by ribosomes.
what happens during transcription?
DNA is copied to mRNA for protein synthesis
what is RNA polymerase?
multi-protein complex that catalyses the synthesis of an RNA molecule from a DNA template.
how many types of RNA polymerase are there in prokaryotes and eukaryotes?
1 type in prokaryotes
3 types in eukaryotes
what are the three types of RNA polymerase?
RNA polymerase I - transcribe genes encoding ribosomal RNA (rRNA)
RNA polymerase II - transcribe genes encoding mRNA
RNA polymerase III - transcribe genes encoding tRNA and rRNA.
where does initiation begin?
at a specialised upstream DNA sequence known as a promoter, which contains a rich AT sequence known as a TATA box.
what proteins bind to promoter sites to initiate transcription?
basal or general transcription factors.
what is the transcription initiation complex?
RNA polymerase II and other transcription factors.
this involves:
- transcription factor TFIID - binds to the TATA box
- contains TATA binding protein (TBP) sub-unit
- TFIIA and TFIIB then bind following this
- aided by the transcription factors already in place, RNA polymerase binds to the DNA strand at the start site for transcription.
- additional factors must still bind to the complex before transcription can begin.
what are the transcription factors called that link the basal transcription factors to another type of transcription factor called activators.
co-activators
what do activators do?
increase or decrease the rate of transcription.
what do activators bind to which increase the rate of transcription?
Activators bind to another sequence in the DNA strand called enhancers which can increase the rate of transcription
what do transcription factors called repressors do?
they bind to silencer sequences to decrease the rate of transcription.
what happens during transcription initiation?
hydrogen bonds between DNA strands are broken by RNA polymerase to separate the strands (coding/template and template) near the promotor site
an initiation or transcription bubble is created.
what happens during transcription elongation?
hydrolysis of ATP required to produce energy
RNA polymerase adds ribonucleotides in a 5’ to 3’ direction.
only one strand of DNA is copied.
this is known as the template strand. the other strand is the coding/non- template strand
mRNA is copied using complementary base pairing.
what happens during transcription termination?
a terminator sequence is located downstream of the gene on the DNA strand being copied.
RNA polymerase dissociates from the DNA molecule and the copied strand is released.
the copied strand is known as pre-messenger RNA, it contains introns which need to be removed
what is added following transcription?
a cap and tail are added to the mRNA strand at the 5’ and 3’ end.
what does the Poly-A tail do?
poly-A tail (consists of multiple adenosine monophosphate) - provides stability and facilitates mRNA exit from the nucleus.
what is the 5’ cap?
guanine nucleotide connected to mRNA via triphosphate bridge.
why does RNA splicing happen?
the pre-messenger RNA contains introns that need to be removed to create an mRNA molecule that can be translated to create a protein.
what do introns contain?
introns contain a ‘GU’ sequence at the 5’ end, a ‘AG’ sequence at the 3’, and a consensus sequence including ‘A’
what is the protein complex called that binds to mRNA and cleaved it at the 5’ end of the intron?
spliceosome
what structure is formed as GU binds with A
a looped structure known as a lariat
what does alternative splicing patterns yield?
alternative splicing patterns in the pre-mRNA can yield different RNA strands.
what is tRNA?
Transfer RNA - a “cloverleaf” RNA structure which binds a specific amino acid to a particular codon.
what is a ribosome?
a complex molecular structure containing ribosomal RNA which links the amino acid in the order corresponding to a mRNA transcript.
it has two parts which joint together on the mRNA molecule.
where does the mRNA travel to once it leaves the nucleus in eukaryotes?
travels to the cytoplasm to reach the ribosomes.
how does translation and transcription occur simultaneously in prokaryotes?
In prokaryotes, ribosomes (70S) can attach to the mRNA strand at the same time as transcription is still happening which allows translation to occur simultaneously.
what are the ribosome binding sites in translation?
E site (exit site) for the empty (non-energized) tRNA molecule
P site - (peptidyl-tRNA site) holds the tRNA with the growing polypeptide chain
A site - (aminoacyl-tRNA site) holds the tRNA molecule containing the next amino acid.
what happens during translation initiation?
Small subunit of ribosome attaches to the mRNA strand
tRNA molecule carrying methionine amino acid binds to the AUG start site on the mRNA
Large subunit of ribosome attaches to form initiation complex.
what happens during translation elongation?
Ribosome matches a tRNA molecule to the specific codon next on the mRNA strand
Amino acids linked to produce bond
Process continues producing a sequence of amino acids.
what happens in translation termination?
Termination occurs when the ribosome reaches a stop codon (UAA, UAG, and UGA)
There is no tRNA molecule that corresponds to a stop codon.
A release factor instead binds at the stop codon and polypeptide chain is released, folding onto its 3D dimensional confirmation.
