DNA & Protein Synthesis (AQA A Level Biology): Flashcards
Exam code: 7402
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- FrontThe Genome
Define genome.
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Cards in this collection (49)
Define genome.
The genome is the complete set of genes present in a cell.
Define proteome.
The proteome is the full range of proteins that a cell is able to produce.
Is the proteome usually larger or smaller than the genome?
The proteome is usually larger than the genome.
Why is the proteome larger than the genome?
One gene can produce more than one protein, because of:
Alternative splicing of pre-mRNA
Post-translational modification of proteins (often in the Golgi apparatus)
The full genome is present in every cell, but the genes that are depend on the type.
The full genome is present in every cell, but the genes that are expressed depend on the cell type.
True or False?
Every gene in the genome is expressed in every cell.
False.
The full genome is present in every cell, but only certain genes are expressed, depending on the cell type.
The is the complete set of genes in a cell, whereas the is the full range of proteins it can produce.
The genome is the complete set of genes in a cell, whereas the proteome is the full range of proteins it can produce.
Which nitrogenous base is found in RNA but not in DNA?
Uracil (U) — it replaces thymine.
Which pentose sugar is found in RNA nucleotides?
Ribose.
RNA molecules are made of a single strand, unlike double-stranded DNA.
RNA molecules are made of a single polynucleotide strand, unlike double-stranded DNA.
What is the function of mRNA?
mRNA carries the genetic code from DNA in the nucleus to the ribosomes, where it is used to synthesise proteins during translation.
Describe the structure of a tRNA molecule.
Single-stranded but folded into a clover-leaf shape
Held in shape by hydrogen bonds between complementary bases
Has an anticodon (three unpaired bases) at one end
Has an amino acid binding site at the other end
True or False?
tRNA is a double-stranded molecule.
False.
tRNA is single-stranded but folds into a clover-leaf shape, held together by hydrogen bonds between complementary bases.
mRNA carries the genetic code from the to the , where proteins are made.
mRNA carries the genetic code from the nucleus to the ribosomes, where proteins are made.
Name three types of RNA.
Messenger RNA (mRNA), transfer RNA (tRNA) and ribosomal RNA (rRNA).
Where in the cell does transcription occur?
In the nucleus.
Which enzyme joins the RNA nucleotides together during transcription?
RNA polymerase.
Describe the process of transcription.
The DNA unwinds and the hydrogen bonds between the bases break (catalysed by RNA polymerase)
One strand acts as a template
Free RNA nucleotides align by complementary base pairing
RNA polymerase joins the nucleotides to form mRNA
The mRNA leaves the nucleus through a nuclear pore
In transcription, the DNA strand that is copied is called the strand.
In transcription, the DNA strand that is copied is called the template strand.
True or False?
DNA polymerase is the enzyme that catalyses transcription.
False.
RNA polymerase catalyses transcription. DNA polymerase is used in DNA replication.
Free RNA nucleotides pair with the template strand by base pairing.
Free RNA nucleotides pair with the template strand by complementary base pairing.
How does the mRNA base sequence compare to the DNA coding (non-template) strand?
It is the same sequence, except that uracil replaces thymine.
Define template strand.
The template strand is the DNA strand that is transcribed to produce a complementary mRNA molecule.
Define splicing.
Splicing is the removal of introns (non-coding sequences) and the joining together of exons (coding sequences) to form mature mRNA.
What is pre-mRNA?
The initial transcript produced in eukaryotes, containing both introns and exons, before splicing takes place.
During splicing, are removed and are joined together.
During splicing, introns are removed and exons are joined together.
Why can a single eukaryotic gene code for more than one polypeptide?
Because of alternative splicing — different combinations of exons are joined together to form different mature mRNA molecules, each coding for a different polypeptide.
True or False?
Prokaryotic genes contain introns.
False.
Prokaryotic genes do not contain introns, so no splicing is needed and mRNA is produced directly from DNA.
How does transcription differ between prokaryotes and eukaryotes?
Prokaryotes: no pre-mRNA — mRNA is produced directly (no introns to splice)
Eukaryotes: produce pre-mRNA, which is then spliced to form mature mRNA
In eukaryotes, the whole gene is transcribed to form , which is then spliced to form mature .
In eukaryotes, the whole gene is transcribed to form pre-mRNA, which is then spliced to form mature mRNA.
Where in the cell does translation occur?
In the cytoplasm, on a ribosome.
Describe the process of translation.
The mRNA attaches to a ribosome
tRNA molecules bring specific amino acids to the ribosome
Each tRNA anticodon pairs with a complementary codon on the mRNA
A peptide bond forms between adjacent amino acids (using ATP)
This continues until a stop codon is reached, forming the polypeptide
The tRNA pairs with a complementary on the mRNA.
The tRNA anticodon pairs with a complementary codon on the mRNA.
What provides the energy for peptide bond formation during translation?
ATP (produced by the mitochondria).
How many tRNA molecules fit onto a ribosome at any one time?
Two.
True or False?
Translation takes place in the nucleus.
False.
Transcription occurs in the nucleus; translation occurs in the cytoplasm.
Define codon.
A codon is a sequence of three bases on mRNA that codes for a specific amino acid.
Define anticodon.
An anticodon is a sequence of three unpaired bases on tRNA that is complementary to an mRNA codon.
A bond forms between adjacent amino acids during translation, using energy from .
A peptide bond forms between adjacent amino acids during translation, using energy from ATP.
What three key terms describe the genetic code?
Universal, non-overlapping and degenerate.
What does it mean that the genetic code is degenerate?
Most amino acids are coded for by more than one codon.
Why is the genetic code described as degenerate?
There are 64 possible codons but only 20 amino acids, so most amino acids are coded for by more than one codon.
What does it mean that the genetic code is non-overlapping?
Each base is read only once, as part of a single codon.
What does it mean that the genetic code is universal?
The same codons code for the same amino acids in almost all organisms.
Which codon is the start codon, and which amino acid does it code for?
AUG — it codes for methionine.
What is a stop codon?
A codon that signals the end of translation and does not code for an amino acid (e.g. UAA).
A change in the base sequence does not always change the amino acid sequence, because the genetic code is .
A change in the base sequence does not always change the amino acid sequence, because the genetic code is degenerate.
A segment of mRNA contains 303 coding nucleotides. How many amino acids are in the polypeptide produced?
100 amino acids.
303 ÷ 3 = 101 codons
101 − 1 (for the stop codon) = 100 amino acids
True or False?
You must memorise which codons code for which amino acids.
False.
You are always given a codon table in the exam, so you do not need to recall specific codons.
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