CH2 | The Central Dogma Flashcards
The Central Dogma describes…
how genetic information flows from DNA to a protein product.
Gene expression is the process of…
genetic information flowing from DNA to RNA to protein.
The process of DNA to RNA is…
transcription.
The process of RNA to protein is…
translation.
What is it called when DNA makes more DNA?
Replication.
In the very rare cases when RNA is used to make DNA it’s called…
Reverse transcription.
Transcription copies…
a segment of DNA into RNA.
DNA segments transcribed into RNA that encode proteins are…
messenger RNA (mRNA).
DNA segments copied into RNA that do not encode proteins are…
non-coding RNAs.
mRNA comprises how much of total RNA?
1-3%.
The three steps of transcription are…
Initiation, Elongation, Termination.
The region of DNA where RNA polymerase binds to initiate transcription is the…
Promoter.
The segment of DNA that is transcribed into RNA is called the…
Coding sequence.
The region of DNA that signals the end of transcription is the…
Terminator.
In a gene, the region where RNA polymerase first binds is the…
Promoter.
The +1 site on a gene designates…
the transcription initiation site.
The region of DNA that is transcribed into an RNA molecule is the…
RNA-coding sequence.
The region of a gene that signals the end of transcription is the…
Terminator.
The DNA strand that is used as a guide to make mRNA during transcription is the…
Template strand.
The DNA strand that is not used during transcription and has a nearly identical sequence to the newly made mRNA is the…
Non-template strand.
The region towards the 5’ end of the gene relative to the coding sequence is considered…
upstream.
The region towards the 3’ end of the gene relative to the coding sequence is considered…
downstream.
During transcription, the enzyme that synthesizes RNA is…
RNA polymerase.
The DNA strand used by RNA polymerase to make mRNA is the…
template strand.
Other names for the template strand include the…
on-coding, or anti-sense strand
The newly synthesized RNA molecule is also called…
Nascent mRNA.
The DNA strand not used during transcription is called the…
non-template strand.
Other names for the non-template strand include the…
coding or sense strand.
RNA polymerase adds nucleotides to which end of the growing RNA molecule?
3’ end.
The region where RNA is temporarily bound to DNA during transcription is called the…
RNA-DNA hybrid.
During transcription, the RNA molecule is synthesized in which direction?
5’ to 3’ direction.
What is the direction of the movement of RNA polymerase along the template strand?
3’ to 5’ direction
Transcription in eukaryotes begins at which end of the gene?
3’ end (upstream) in the promoter region.
The TATA box is located how many base pairs upstream of the transcription start site?
Approximately 25-35 base pairs.
What protein binds to the TATA box?
TATA-binding protein (TBP).
TBP recruits what to the promoter?
Transcription factors and RNA polymerase II.
The complex formed at the promoter that initiates transcription is called the…
transcription initiation complex.
Why is the TATA box a common site for DNA unwinding?
Because it is rich in A and T bases, which have fewer hydrogen bonds than G and C, making them easier to separate.
In eukaryotes, the main RNA polymerase enzyme that is involved in transcribing most genes is…
RNA polymerase II
In a eukaryotic promoter, what’s the start point?
Where the actual transcription of the gene begins, designated as +1 on the DNA sequence.
After the transcription initiation complex forms then…
RNA synthesis begins.
During elongation, the template DNA strand is read in which direction?
3’ to 5’ direction.
RNA synthesis during elongation occurs in which direction?
5’ to 3’ direction.
The DNA strand that has a sequence nearly identical to the new mRNA (except for T’s replaced with U’s) is the…
coding strand.
What enzyme catalyzes the formation of phosphodiester bonds between adjacent ribonucleotides in the growing RNA molecule?
RNA polymerase.
What are the differences between the sequences in the mRNA and coding strand?
The base sequences are identical except T in DNA is replaced by U in RNA.
The region of DNA that signals the end of transcription is the…
terminator.
During termination, what happens when RNA polymerase recognizes the termination sequence?
It changes conformation, releasing itself from the template strand, and stops transcription.
What happens to the DNA template during termination?
It rewinds back into a double helix.
The RNA molecule released at the end of transcription is called…
Pre-mRNA.
During transcription, which DNA strand is read to synthesize RNA?
The template strand.
What is the corresponding RNA base for Adenine (A) in DNA during transcription?
Uracil (U).
What is the corresponding RNA base for Thymine (T) in DNA?
Adenine (A).
What is the corresponding RNA base for Cytosine (C) in DNA?
Guanine (G).
What is the corresponding RNA base for Guanine (G) in DNA?
Cytosine (C).
In what direction is the template DNA strand read?
3’ to 5’ direction.
In what direction is the RNA molecule synthesized?
5’ to 3’ direction.
Where is pre-mRNA produced?
In the nucleus.
Pre-mRNA is transcribed from what type of chromosome?
Linear.
What three processing steps must pre-mRNA undergo to become mature mRNA?
5’ capping, poly-A tail addition, and splicing.
The addition of a methylated guanine to the 5’ end of pre-mRNA is called…
5’ capping.
The addition of a string of adenine nucleotides to the 3’ end of pre-mRNA is called…
poly-A tail addition.
The process of removing introns from pre-mRNA is called…
Splicing.
What are the regions of pre-mRNA that are removed during splicing?
Introns.
What are the regions of pre-mRNA that are retained and joined together during splicing?
Exons.
What region in mRNA is translated to a protein?
The protein-coding region.
What regions are present in pre-mRNA that are not translated into the final protein sequence?
5’ and 3’ UTR.
One function of the 5’ cap and poly-A tail is to facilitate…
nucleocytoplasmic transport of mRNA.
The 5’ cap and poly-A tail protect mRNA from degradation by…
exonucleases.
How does the poly-A tail length affect mRNA stability and translation?
Shortening can trigger degradation; lengthening can enhance stability and translation.
The 5’ cap helps in the recognition of mRNA by…
translational machinery (ribosomes).
What do the 5’ cap and poly-A tail ensure during translation?
They distinguish between immature and mature mRNA, ensuring that only mature mRNA is translated.
Alternative splicing is a process where…
exons from the same gene are joined in different combinations.
Alternative splicing leads to the production of…
different, but related, mRNA transcripts.
Different mRNAs produced by alternative splicing can be translated into proteins with…
distinct structures and functions.
The main function of alternative splicing is to…
increase the diversity of mRNAs and proteins expressed from a single gene.
Alternative splicing increases the transcriptome size from approximately 21,000 genes to…
around 200,000 transcripts.
In a eukaryotic gene, the region where RNA polymerase binds to initiate transcription is the…
Promoter.
The initial RNA molecule transcribed from DNA, which includes both introns and exons, is called the…
Primary transcript (or pre-mRNA).
The non-coding sequences within the primary transcript that are removed during RNA processing are…
Introns.
The coding sequences within the primary transcript that are retained and joined together to form mature mRNA are…
Exons.
What are the three main processing steps that convert a primary transcript into mature mRNA?
Capping, splicing, and polyadenylation.
What is added to the 5’ end of the mRNA during capping?
A 7-methylguanosine (7-mG) cap.
What is added to the 3’ end of the mRNA during polyadenylation?
A poly-A tail (100-200 adenine nucleotides).
The regions at the beginning and end of the mRNA that are not translated into protein are called…
5’ UTR and 3’ UTR (untranslated regions).
The genetic code defines how the four-letter DNA code is translated into…
the 20-letter amino acid code.
A unit of three adjacent nucleotides in mRNA that codes for an amino acid is called a…
codon.
How many possible codons are there?
64 (4 bases ^ 3 positions = 64).
Why is the genetic code described as degenerate or redundant?
Because a single amino acid can be coded for by more than one codon.
What is the start codon and what amino acid does it code for?
AUG, Methionine.
What are the three stop codons?
UAA, UAG, UGA.
How do you determine the amino acid sequence from an mRNA sequence?
Divide the mRNA into codons (3 nucleotides each), then use the genetic code table to find the corresponding amino acid for each codon.
If an mRNA sequence is 5’-AUGCCUAGU-3’, what is the first codon?
5’-AUG-3’
Using the genetic code table, what amino acid does the codon 5’-AUG-3’ code for?
Methionine.
How do you find the number of amino acids a given mRNA will make?
Divide the number of nucleotides by 3 since every codon is 3 nucleotides long, but remember to not count the stop codon since it does not make an amino acid.
Using the genetic code table, what amino acid does the codon 5’-CAU-3’ code for?
Histidine (His).
Using the genetic code table, what amino acid does the codon 5’-GGG-3’ code for?
Glycine (Gly).
Using the genetic code table, what amino acid does the codon 5’-UCA-3’ code for?
Serine (Ser).
Using the genetic code table, what does the codon 5’-UAG-3’ code for?
Stop codon.
What are the possible codons for the amino acid Leucine (Leu), according to the genetic code table?
UUA, UUG, CUU, CUC, CUA, CUG.
What are the possible codons for the amino acid Alanine (Ala)?
GCU, GCC, GCA, GCG.
If a codon is mutated from 5’-UUU-3’ to 5’-UUC-3’, what is the effect on the amino acid sequence?
No effect, both code for Phenylalanine (Phe). This demonstrates the redundancy of the genetic code.
Translation is the process where information in mRNA directs…
the addition of amino acids during protein synthesis.
What are the three types of RNA involved in translation?
mRNA (messenger RNA), tRNA (transfer RNA), and rRNA (ribosomal RNA).
What is the role of mRNA in translation?
Carries the genetic code from DNA that specifies the amino acid sequence.
What is the role of tRNA in translation?
Brings specific amino acids to the ribosome, matching its anticodon to the mRNA codon.
What is the role of rRNA in translation?
Forms part of the ribosome, the machinery that synthesizes proteins.
The region on tRNA that is complementary to the mRNA codon is the…
anticodon.
What is the function of the ribosome in translation?
It provides the site for protein synthesis, where mRNA and tRNA interact and amino acids are linked together.
What is the growing chain of amino acids called during translation?
A polypeptide.
What type of bond is formed between amino acids during translation?
A peptide bond.
If a codon in mRNA is 5’-AUG-3’, what would be the anticodon sequence on the tRNA?
3’-UAC-5’. (Remember, the anticodon is complementary and antiparallel to the codon)
What does it mean that tRNA and mRNA interact in an antiparallel manner?
The 5’ end of the mRNA codon pairs with the 3’ end of the tRNA anticodon, and vice-versa.
Ribosomes are made of…
both RNA (rRNA) and protein.
What is the main function of ribosomes in the cell?
They are the site of protein synthesis.
What are the two main functions of rRNA in the ribosome?
1) Ensure proper alignment of mRNA and ribosome.
2) Catalyze peptide bond formation.
What are the two subunits of a ribosome?
The large subunit and the small subunit.
What are the three binding sites on the ribosome for tRNA molecules?
A site, P site, and E site.
What does the A site on the ribosome stand for and what is its function?
Aminoacyl-tRNA binding site; holds the tRNA carrying the next amino acid to be added.
What does the P site on the ribosome stand for and what is its function?
Peptidyl-tRNA binding site; holds the tRNA carrying the growing polypeptide chain.
What does the E site on the ribosome stand for and what is its function?
Exit site; where discharged tRNAs leave the ribosome.
In what order does an mRNA molecule move through the ribosome binding sites?
A site, then P site, then E site.
Where does the very first tRNA carrying Methionine bind on the ribosome?
It binds directly to the P site, subsequent tRNAs first bind to the A site.
When does the polypeptide exit from the ribosome?
It exits from the P site after a new peptide bond is formed and the ribosome has moved along the mRNA, transferring the polypeptide to the tRNA in the A site.
What is the main function of tRNA?
To carry amino acids to the ribosome during translation.
The characteristic shape of a tRNA molecule is described as…
a cloverleaf.
What is the name of the three-base sequence on tRNA that is complementary to the mRNA codon?
Anticodon.
To which end of the tRNA molecule does the amino acid attach?
The 3’ end.
What is the name of the enzyme that attaches the correct amino acid to a tRNA molecule?
Aminoacyl-tRNA synthetase.
A tRNA molecule that has an amino acid attached is said to be…
charged.
How does the tRNA anticodon interact with the mRNA codon?
Through complementary base pairing (A with U, G with C).
What is the first step in the initiation of translation?
The small ribosomal subunit binds to the 5’ cap of the mRNA.
What is the start codon that the ribosome scans for in the mRNA?
AUG.
In what direction does the ribosome scan the mRNA to find the start codon?
5’ to 3’ direction.
What is the initiator tRNA in eukaryotes and what amino acid does it carry?
Initiator tRNA is tRNA that carries methionine (Met).
To which site on the ribosome does the initiator tRNA (Met) bind?
The P site.
Once the initiator tRNA is bound to the start codon, what happens next?
The large ribosomal subunit joins the complex.
How is the translational reading frame established?
By the position of the start codon (AUG), which dictates that subsequent codons are read as groups of three nucleotides.
Which part of the ribosome initially binds to the mRNA to hold it in place?
Small ribosomal subunit.
Where is the initiator tRNA located in the fully assembled ribosome?
P site
Elongation in translation refers to…
the addition of amino acids to the growing polypeptide chain.
During elongation, which tRNA binding site on the ribosome holds the growing polypeptide chain?
The P site.
During elongation, where does a new tRNA carrying an amino acid bind?
To the A site.
What happens to the polypeptide chain when a new tRNA binds to the A site?
The polypeptide chain is transferred from the tRNA in the P site to the amino acid on the tRNA in the A site.
What is the movement of the ribosome along the mRNA during elongation called?
Translocation.
During translocation, the ribosome moves down by how many codons?
One codon.
What happens to the tRNA that was in the P site after the polypeptide chain is transferred?
It moves to the E site and then exits the ribosome.
What happens to the tRNA in the A site after translocation?
It moves to the P site, carrying the polypeptide chain.
The state in which an incoming tRNA brings a new amino acid to the A site is known as…
the pre-translocation state.
The state after which the ribosome moves one codon down the mRNA, the empty tRNA leaves the E site, the tRNA carrying the polypeptide moves from the A site to the P site is known as…
the post-translocation state.
What marks the termination of translation?
The presence of a stop codon in the mRNA.
What are the three stop codons?
UAA, UAG, UGA.
Do stop codons code for any amino acid?
No.
What binds to the ribosome when a stop codon is in the A site?
A release factor protein.
What is the effect of the release factor binding to the ribosome?
It causes the ribosome, mRNA, and the newly synthesized polypeptide to dissociate.
What happens to the ribosomal subunits after termination?
They can be recycled and used for another round of translation.
What happens to the mRNA after termination?
The mRNA can be reused for another round of translation, or be degraded.
