DNA Structure Flashcards
(24 cards)
Describe how a phosphodiester bond is formed between two nucleotides within a DNA
molecule.
condensation reaction between deoxyribose and phosphate group
catalysed by DNA polymerase
In the process of semi-conservative DNA replication, the two strands within a DNA
molecule are separated. Each then acts as a template for the formation of a new
complementary strand.
Describe how the separation of strands occurs.
DNA helicase breaks hydrogen bonds between complementary base pairs
The nucleus and a chloroplast of a plant cell both contain DNA.
Give three ways in which the DNA in a chloroplast is different from DNA in the nucleus.
IN CHLOROPLAST
DNA SHORTER
DNA IS CIRCULAR NOT LINEAR
DNA IS NOT ASSOCIATED WITH HISTONES
DNA HAS FEWER GENES
Some DNA nucleotides have the organic base thymine, but RNA nucleotides do not have
thymine. RNA nucleotides have uracil instead of thymine.
Give one other difference between the structure of a DNA nucleotide and the structure of
an RNA nucleotide.
DNA has deoxyribose sugar whereas RNA has ribose
Not all mutations in the nucleotide sequence of a gene cause a change in the structure of a
polypeptide.
Give two reasons why.
Triplets code for the same amino acids
Occurs in introns
DNA is a polymer of nucleotides. Each nucleotide contains an organic base.
Explain how the organic bases help to stabilise the structure of DNA.
Hydrogen bonds between the base pairs hold the strands together
Many Hydrogen bonds provide strength
Suggest one advantage of showing the genetic code as base sequences on mRNA, rather
than triplets on DNA.
DNA has two strands each with a different (complementary) base sequence;
What name is given to a group of three bases on mRNA that codes for an amino acid?
codon
Use information from Table 1 to explain why the genetic code is described as degenerate.
some amino acids have more than one codon
Suggest the role of the mRNA base triplets UGA, UAG and UAA.
stop translation
Result in detachment of polypeptide chain from ribosome
Describe two differences between the structure of a tRNA molecule and the structure of an
mRNA molecule.
tRNA is a clover leaf shape
tRNA has an amino acid binding site
The length of a gene is described as the number of nucleotide base pairs it contains.
Use information in above diagram to calculate the length of a gene containing 4.38 × 103
base pairs.
1861
In a eukaryotic cell, the structure of the mRNA used in translation is different from the
structure of the pre-mRNA produced by transcription.
Describe and explain a difference in the structure of these mRNA molecules
mRNA has fewer nucleotides
pre-mRNA has exons and introns
because of splicing
Why is the genetic code described as being universal?
the same triplet codes for the same amino acid;
The genetic code uses four different DNA bases. What is the maximum number of
different DNA triplets that can be made using these four bases?
64
Transcription of a gene produces pre-mRNA.
(b)
Name the process that removes base sequences from pre-mRNA to form mRNA.
splicing
Mutation 1 leads to the production of a non-functional protein.
Explain why.
mutation changes triplets/codons causing frame shift
changes the specific sequence of amino acid
hydrogen bonds form in different places they are affected
tertiary structure changes/unfolds of protein so non-functional
DNA is a polymer. What is the evidence from the diagram that DNA is a polymer?
Repeating units / nucleotides / monomer / molecules;
What effect might mutation 2 have on the protein produced?
Explain your answer.
Intron non-coding (DNA) / only exons coding;
(So) not translated / no change in mRNA produced / no effect (on protein)
A polypeptide has 51 amino acids in its primary structure.
What is the minimum number of DNA bases required to code for the amino acids in
this polypeptide?
153
The gene for this polypeptide contains more than this number of bases.
explain why
some regions of the gene are non-coding they have introns
Name the two substances that make up part X.
ribose
phosphate
Explain the difference between pre-mRNA and mRNA.
pre-mRNA contains introns
mRNA has exons
Explain why the percentages of bases from the middle part of the chromosome and
the end part are different.
Have different (base) sequences / combinations of (bases);
(Pre-mRNA) transcribed from different DNA / codes for different proteins;
