D1.2 SL
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113 Terms
What is transcription?
The synthesis of RNA using a DNA template.
What enzyme carries out transcription?
RNA polymerase.
What does RNA polymerase do?
It reads the DNA template and builds a complementary RNA strand.
In which direction does RNA polymerase read the DNA template?
3′ → 5′.
In which direction does RNA polymerase build RNA?
5′ → 3′.
Does RNA polymerase need a primer?
No.
What is the difference between transcription and replication?
Transcription produces RNA from a DNA template; replication copies DNA for cell division.
What happens during transcription initiation?
RNA polymerase binds to the gene, causing the DNA to open so the template strand can be read.
What happens during transcription elongation?
RNA polymerase adds RNA nucleotides to build a complementary mRNA strand.
What happens during transcription termination?
RNA polymerase reaches the end of the gene, mRNA detaches, and DNA reforms its original double helix.
What is the role of hydrogen bonding in transcription?
It allows complementary bases to pair between the DNA template and the growing RNA strand.
Which base replaces thymine in RNA?
Uracil (U).
What is the antisense DNA strand?
The template strand used to produce mRNA.
How is the antisense strand related to mRNA?
It is complementary to mRNA.
What is another name for the antisense strand?
The non-coding strand.
What is the sense DNA strand?
The coding strand, which has the same sequence as mRNA except that DNA has T instead of U.
How does the mRNA sequence compare with the sense DNA strand?
It has the same base sequence except that U replaces T.
What is the difference between the sense and antisense strands?
The antisense strand is the template complementary to mRNA; the sense strand matches mRNA except for T instead of U.
Why is the DNA double helix stable?
Its closed double-helix structure helps prevent degradation.
What happens to DNA during transcription?
The double helix briefly opens so the template can be read.
What happens to DNA after transcription?
It closes again and reforms its original double helix.
Why must DNA remain stable?
It must be available to be used many times.
What is gene expression?
The use of genetic information to produce products, including proteins.
Why is transcription necessary for gene expression?
It produces the RNA needed for protein synthesis.
Do all cells in an organism contain all the organism's genes?
Yes, according to the slides.
What determines which proteins a cell produces?
Which genes are transcribed.
What happens to genes for proteins a cell needs?
They are switched on.
What happens to genes for proteins a cell does not need?
They are switched off.
How can gene expression affect cell function?
Different genes are transcribed, producing different proteins that determine cell function.
What is translation?
The synthesis of a polypeptide using mRNA.
Where does translation occur?
On ribosomes.
What is a polypeptide?
A chain of amino acids that folds into a three-dimensional structure.
What determines the primary structure of a protein?
The sequence of codons on mRNA.
What is a codon?
A sequence of three mRNA bases that usually codes for a specific amino acid.
How many bases make up one codon?
Three.
What determines the amino acid sequence of a polypeptide?
The mRNA sequence interpreted according to the genetic code.
How many different amino acids are coded for?
20.
What is the start codon?
AUG.
Which amino acid is coded for by AUG?
Methionine.
Which amino acid is normally the first amino acid in a newly made polypeptide?
Methionine.
Can the first methionine be removed after translation?
Yes.
What is the function of a stop codon?
It signals the ribosome to stop translation.
Does a stop codon code for an amino acid?
No.
What is a peptide bond?
A bond that joins amino acids together.
How are peptide bonds formed?
By a condensation reaction.
What is the role of the genetic code in translation?
It determines which amino acids are added according to the mRNA codons.
What is an essential amino acid?
An amino acid the body cannot produce and must obtain from the diet.
What is a non-essential amino acid?
An amino acid the body can produce.
What is a conditionally non-essential amino acid?
An amino acid the body can produce, but not always quickly enough to meet certain needs.
When might conditionally non-essential amino acids need to be obtained from the diet?
During conditions such as infancy or pregnancy.
What is protein deficiency malnutrition?
A condition in which a shortage of essential amino acids prevents the production of specific proteins.
What determines the health effects of protein deficiency malnutrition?
Which amino acid is in short supply.
What is phenylketonuria (PKU)?
A genetic condition that impairs the metabolism of phenylalanine.
What type of inheritance is PKU associated with in the slides?
Autosomal recessive inheritance.
Which gene is mutated in PKU according to the slides?
The gene encoding phenylalanine hydroxylase (PAH).
What does phenylalanine hydroxylase normally do?
It converts excess phenylalanine into tyrosine.
What happens to excess phenylalanine in people with PKU?
It is instead converted into phenylpyruvate, also called phenylketone.
What can build up in the blood and urine of a person with PKU?
Phenylketones.
Why can untreated PKU be harmful?
The buildup of phenylalanine and related compounds can cause serious medical problems.
Why may infants with PKU appear normal at birth?
During pregnancy, the mother can break down phenylalanine.
How is PKU diagnosed according to the slides?
With a blood test for elevated phenylalanine levels shortly after birth.
How is PKU treated?
With a diet that restricts phenylalanine and includes an appropriate medical formula.
Why is phenylalanine restricted in the PKU diet?
To prevent it from building up in the body.
What does the medical formula used in PKU treatment provide?
Precise quantities of essential amino acids.
What can happen if PKU is diagnosed early and the diet is maintained?
The person can have a normal lifespan without damaging symptoms.
What is the role of mRNA in translation?
It carries instructions for making a protein from the nucleus to the site of translation.
Where is mRNA produced?
In the nucleus, during transcription.
How does mRNA leave the nucleus?
Through nuclear pores.
What does mRNA bind to at the ribosome?
The small ribosomal subunit.
How many tRNAs can bind simultaneously to the large ribosomal subunit according to the slides?
Two.
Which organelle carries out translation?
The ribosome.
Where are functioning ribosomes found?
Free in the cytoplasm or attached to the rough endoplasmic reticulum.
What is the role of tRNA?
It brings the appropriate amino acid to the ribosome.
What is tRNA made of?
RNA.
From what type of DNA is tRNA transcribed according to the slides?
“Non-coding” DNA.
What is the characteristic shape of tRNA?
A cloverleaf structure.
What holds tRNA in its cloverleaf shape?
Hydrogen bonds between complementary nucleotides.
Where is the amino acid attached to tRNA?
At the 3′ end.
What is an anticodon?
A sequence of three bases on tRNA that pairs with a complementary mRNA codon.
How does complementary base pairing help translation?
It allows the tRNA anticodon to pair with the correct mRNA codon.
What is the anticodon complementary to the mRNA codon AUG?
UAC.
What is the role of the ribosome in protein synthesis?
It reads mRNA and helps join amino acids by peptide bonds.
What happens when mRNA enters a ribosome?
The ribosome reads its codons during translation.
What can happen to a polypeptide made by a ribosome attached to the rough ER?
It enters the ER lumen and travels through the ER before being released in vesicles.
What does the A site of the ribosome stand for?
Aminoacyl site.
What does the P site of the ribosome stand for?
Peptidyl site.
What does the E site of the ribosome stand for?
Exit site.
What is found at the P site during elongation?
The tRNA carrying the growing polypeptide.
Where does the next amino acid join the ribosome?
At the A site, carried by a tRNA.
What happens when the amino acids are joined during translation?
A peptide bond forms between them.
How far does the ribosome move along mRNA during each step?
One codon toward the 3′ end.
What happens to the tRNA that was at the A site after the ribosome moves?
It moves into the P site.
What happens to the tRNA that was at the P site after the ribosome moves?
It moves into the E site after its amino acid has been transferred.
What happens to the tRNA at the E site?
It exits the ribosome.
What happens after a tRNA moves from the A site to the P site?
Another tRNA carrying the next amino acid can enter the A site.
What is the repeated cycle of translation responsible for?
Extending the growing polypeptide chain one amino acid at a time.
How does the ribosome help form a polypeptide?
It acts as an enzyme that helps amino acids bond through peptide bonds.
What does degenerate genetic code mean?
One amino acid can be coded for by more than one codon.
What advantage does a degenerate genetic code provide?
Some mutations are silent and do not change the amino acid sequence or protein structure.
What is a silent mutation in the context of the slides?
A DNA change that does not lead to a change in the amino acid sequence.