Structure of Nucleic Acids & Replication of DNA (Cambridge (CIE) AS Biology): Flashcards
Exam code: 9700
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- FrontNucleotides
Define nucleotide.
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Cards in this collection (23)
Define nucleotide.
A nucleotide is made of a phosphate group, a pentose sugar and a nitrogenous base.
What are the three components of a nucleotide?
A phosphate group
A pentose sugar
A nitrogenous base
Describe the structure of ATP.
ATP is a phosphorylated nucleotide.
It consists of the base adenine, the pentose sugar ribose and three phosphate groups.
Which bases are purines, and what is their structure?
Adenine and guanine are purines.
They have a double ring structure.
Which bases are pyrimidines, and what is their structure?
Cytosine, thymine and uracil are pyrimidines.
They have a single ring structure.
Adenine and guanine are purines with a ring structure.
Adenine and guanine are purines with a double ring structure.
What does it mean that the two DNA strands are antiparallel?
The two strands run in opposite directions.
One runs 5' to 3' and the other runs 3' to 5'.
What are the complementary base pairing rules in DNA?
Adenine (A) pairs with thymine (T).
Cytosine (C) pairs with guanine (G).
How does the hydrogen bonding differ between C–G and A–T base pairs?
C–G pairs are joined by three hydrogen bonds.
A–T pairs are joined by two hydrogen bonds.
Which bonds link the nucleotides along a single DNA strand?
Phosphodiester bonds link adjacent nucleotides, joining the phosphate of one to the sugar of the next.
The two strands of a DNA molecule are twisted into a helix.
The two strands of a DNA molecule are twisted into a double helix.
True or False?
C–G base pairs are held together by two hydrogen bonds.
False.
C–G pairs are held by three hydrogen bonds; A–T pairs are held by two.
What is semi-conservative replication?
DNA replication in which each new DNA molecule contains one original (template) strand and one newly synthesised strand.
During which stage of the cell cycle does DNA replication occur?
The S phase (synthesis phase) of interphase.
What is the role of DNA polymerase in replication?
It catalyses the addition of new nucleotides to the growing strand by complementary base pairing.
It can only add nucleotides in the 5' to 3' direction.
What is the role of DNA ligase in replication?
It joins the fragments of the lagging strand together by forming bonds in the sugar–phosphate backbone.
Why is the leading strand made continuously but the lagging strand in fragments?
DNA polymerase can only add nucleotides in the 5' to 3' direction.
The leading strand is synthesised continuously towards the replication fork.
The lagging strand is synthesised in short fragments away from the fork.
Replication is described as because each new molecule keeps one original strand.
Replication is described as semi-conservative because each new molecule keeps one original strand.
Give three differences between an RNA molecule and a DNA molecule.
RNA is single-stranded; DNA is double-stranded.
RNA contains the sugar ribose; DNA contains deoxyribose.
RNA contains the base uracil; DNA contains thymine.
What is mRNA (messenger RNA)?
A single-stranded RNA molecule that carries a copy of the genetic code from the DNA to the ribosomes.
Which pentose sugar is found in an RNA molecule?
Ribose.
In RNA, the base uracil replaces the base found in DNA.
In RNA, the base uracil replaces the base thymine found in DNA.
True or False?
An mRNA molecule is double-stranded.
False.
mRNA is single-stranded.
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