DNA & Gene Expression (Edexcel International A Level (IAL) Biology): Flashcards
Exam code: YBI11
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- FrontDNA Replication
Semi-conservative replication
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Semi-conservative replication
Semi-conservative replication is the process by which a new DNA molecule consists of one original DNA strand and one newly synthesized strand.
Why is DNA replication necessary before a cell divides?
DNA replication is necessary before cell division so that each daughter cell receives a full copy of the parental DNA.
During DNA replication, the enzyme breaks the hydrogen bonds between base pairs.
During DNA replication, the enzyme helicase breaks the hydrogen bonds between base pairs.
DNA polymerase
DNA polymerase is an enzyme that synthesises new DNA strands by catalysing condensation reactions between nucleotides.
The new DNA strand is made up of nucleotides joined together by bonds to form the sugar-phosphate backbone.
The new DNA strand is made up of nucleotides joined together by phosphodiester bonds to form the sugar-phosphate backbone.
How does DNA polymerase make sure each new DNA strand is an exact copy of the original?
DNA polymerase adds free nucleotides that pair with their complementary bases on the template strand (adenine with thymine, cytosine with guanine), so each new strand is a complementary copy of the original.
Template strand
A template strand is one of the two separated original DNA strands; each acts as a pattern that free nucleotides base-pair with to build a new complementary strand during replication.
DNA replication occurs during the phase of the cell cycle, which is part of interphase.
DNA replication occurs during the S phase of the cell cycle, which is part of interphase.
True or False?
Both strands of the new DNA molecule are newly synthesised during semi-conservative replication.
False.
In semi-conservative replication, one strand is from the original DNA molecule and the other is newly synthesised.
What is the importance of retaining one original DNA strand during replication?
Retaining one original DNA strand ensures genetic continuity between generations of cells, so new cells inherit all their genes from parent cells.
Who performed the experiment that provided evidence for semi-conservative replication of DNA?
The experiment was performed by Matthew Meselson and Franklin Stahl.
In Meselson and Stahl's experiment, DNA containing nitrogen settled at the bottom of the centrifuge tube, while DNA with both heavy and light nitrogen settled in the of the tube.
In Meselson and Stahl's experiment, DNA containing heavy nitrogen settled at the bottom of the centrifuge tube, while DNA with both heavy and light nitrogen settled in the middle of the tube.
True or False?
Meselson and Stahl's results showed that DNA replication is conservative.
False.
Their results showed that DNA replication is semi-conservative, not conservative.
Triplet code
A triplet code is a sequence of three nucleotide bases in DNA that codes for one amino acid.
Each sequence of bases in a gene codes for amino acid.
Each sequence of three bases in a gene codes for one amino acid.
What is the function of start and stop codons in the genetic code?
Start and stop codons tell the cell where individual genes start and stop, ensuring the correct reading of the genetic code and production of proteins.
Non-overlapping code
A non-overlapping code is one in which each base is only read once in the sequence; adjacent codons do not overlap.
True or False?
The genetic code is non-overlapping, so a single base can be part of more than one codon.
False.
In a non-overlapping code, each base is only read once, so a single base cannot be part of more than one codon.
There are different codons but only amino acids commonly found in proteins.
There are 64 different codons but only 20 amino acids commonly found in proteins.
What does it mean that the genetic code is degenerate?
The genetic code is degenerate, meaning that more than one codon can code for the same amino acid.
True or False?
The genetic code is universal, meaning it is the same in almost all living things.
True.
The genetic code is universal, so the same triplet codes code for the same amino acids in nearly all organisms.
Gene
A gene is a sequence of nucleotides that forms part of a DNA molecule and codes for the production of a specific polypeptide (protein).
A gene is a sequence of that forms part of a DNA molecule and codes for a .
A gene is a sequence of nucleotides that forms part of a DNA molecule and codes for a specific polypeptide (protein).
What does a gene code for?
A gene codes for the production of a specific polypeptide (protein).
Protein molecules are made up of a series of bonded together.
Protein molecules are made up of a series of amino acids bonded together.
What determines the shape and behaviour of a protein molecule?
The exact sequence of amino acids determines the shape and behaviour of a protein molecule.
True or False?
Genes in DNA control protein structure by determining the sequence in which amino acids join together.
True.
Genes in DNA determine the exact sequence of amino acids that join together during protein synthesis, thus controlling protein structure and function.
Central dogma
Crick's central dogma describes the one-way flow of genetic information in a cell: from DNA to mRNA to protein.
A of three bases in a gene codes for one .
A triplet of three bases in a gene codes for one amino acid.
Gene
A gene is a sequence of nucleotide bases in a DNA molecule that codes for the production of a specific sequence of amino acids, which make up a specific polypeptide (protein).
What are the two main stages of protein synthesis?
The two main stages of protein synthesis are transcription and translation.
During transcription, a segment of DNA and the hydrogen bonds between complementary base pairs .
During transcription, a segment of DNA unwinds and the hydrogen bonds between complementary base pairs break.
The enzyme responsible for catalysing the formation of an mRNA molecule during transcription is .
The enzyme responsible for catalysing the formation of an mRNA molecule during transcription is RNA polymerase.
Antisense strand
The antisense strand is the template strand of DNA that is transcribed to produce an mRNA molecule during transcription.
Which base in RNA replaces thymine found in DNA?
In RNA, the base uracil replaces thymine found in DNA.
The mRNA molecule leaves the via a pore in the nuclear envelope after transcription.
The mRNA molecule leaves the nucleus via a pore in the nuclear envelope after transcription.
Anticodon
An anticodon is a triplet of unpaired bases at one end of a tRNA molecule that pairs with a complementary codon on mRNA during translation.
Where does translation occur in a cell?
Translation occurs in the cytoplasm of the cell, at the ribosome.
The sequence of three bases on mRNA that codes for a specific amino acid is called a .
The sequence of three bases on mRNA that codes for a specific amino acid is called a codon.
The start codon on mRNA is , which codes for the amino acid .
The start codon on mRNA is AUG, which codes for the amino acid methionine.
True or False?
tRNA molecules each carry a specific amino acid to the ribosome during translation.
True.
Each tRNA molecule has a specific anticodon and carries a specific amino acid to the ribosome for translation.
Peptide bond
A peptide bond is a chemical bond formed between two amino acids during a condensation reaction in translation.
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