GCU BIO 319: LATEST A+ QUESTIONS AND ANSWERS
GUIDE FOR ULTIMATE SUCCESS
What are the types of DNA damage?
Deamination, UV damage, Alkylation, depuration/ depyrimidation, oxidation, and strand breaks
What is deamination?
when water makes ammonia and creates uracil instead of cytosine.
What is UV damage?
UV light causes cross linking within the strand. Most often occurs at thymine causing thymidine dimer.
What is alkylation?
when a bulky group joins onto a base (G, C, A, T).
what is depuration/depyrimidation?
when the bond between the sugar and base in DNA gets broken because of hydrolysis leading to the loss
of a base in DNA (Backbone is still intact). This led to polymerase not knowing what to put next.
What is oxidation?
when something reacts with oxygen causing the removal of a base, the modification of sugar and breaks
backbone, or damage to base. Every part of nucleotide can be attacked by oxidation
What is a strand break?
Can be caused by oxidation. It's when the DNA strand breaks.
- single stranded break repairs itself
- double stranded break
Can be caused by oxidation
What does unrepaired DNA damage lead to?
a mutation
What is a mutation?
a persistent change in the sequence of DNA that remains unrepaired and is carried over through
generations.
What are the different types of mutations?
point mutation, insertions and deletions, and rearrangements
What are the different types of point mutations?
, -> silent: only changes the base at the end of the codon is changed ( no change to amino acid )
-> nonsense: causes a premature stop codon , only changes the base at the front codon
-> missense: changes the middle base in codon.
What are insertions and deletions?
When a nucleotide pair is lost or gained in a gene, causing a frameshift.
What are rearrangements?
When pieces of chromosomes are missing, duplicated (there are extra copies), or moved around
What are the different types of DNA repair mechanisms?
Direct reversal of DNA damage, excision repair, double stranded break repair
Name an example of direct reversal of DNA.
Photolyase (an enzymes) reversing pyrimidine dimers
What are the key steps of photolyase reversing the DNA?
1. Photolyase recognizes dimers.
2. Energy from visible light is used by photolyase to break (remove) the cyclobutene ring, linking the
bases. This process is called photo reactivation (reverses crosslinks).
What is the difference between gene knockout and gene knockdown?
Gene knockdown - temporary reduction of the expression of a gene.
Gene knockout - permanently getting rid of gene.
What methods are used for knockout and knockdown gene expression.
Gene editing is used for gene knockout by using CRISPR/ Cas 9 to modify DNA and completely get rid of
the gene.
RNA interference (RNAi) is used for gene knockdown at the mRNA level. siRNA or miRNA degrade or
inhibit the translation of specific messenger RNA molecules to knockdown the gene expression. (done
naturally )
What is FISH?
Fluorescence In Situ Hybridization.
Uses fluorescent nucleotides to make the chromosomes they want to look at light up.
What are the 4 main steps of FISH?
1. The cell needs to be fixed (pauses/freezes the cells). To do that formaldehyde is used to fix the cells
making the proteins inside the cell stick together. This makes it easier to analyze and study them.
2. A probe is designed by taking a DNA strand that's complementary to the chromosomal region of
GUIDE FOR ULTIMATE SUCCESS
What are the types of DNA damage?
Deamination, UV damage, Alkylation, depuration/ depyrimidation, oxidation, and strand breaks
What is deamination?
when water makes ammonia and creates uracil instead of cytosine.
What is UV damage?
UV light causes cross linking within the strand. Most often occurs at thymine causing thymidine dimer.
What is alkylation?
when a bulky group joins onto a base (G, C, A, T).
what is depuration/depyrimidation?
when the bond between the sugar and base in DNA gets broken because of hydrolysis leading to the loss
of a base in DNA (Backbone is still intact). This led to polymerase not knowing what to put next.
What is oxidation?
when something reacts with oxygen causing the removal of a base, the modification of sugar and breaks
backbone, or damage to base. Every part of nucleotide can be attacked by oxidation
What is a strand break?
Can be caused by oxidation. It's when the DNA strand breaks.
- single stranded break repairs itself
- double stranded break
Can be caused by oxidation
What does unrepaired DNA damage lead to?
a mutation
What is a mutation?
a persistent change in the sequence of DNA that remains unrepaired and is carried over through
generations.
What are the different types of mutations?
point mutation, insertions and deletions, and rearrangements
What are the different types of point mutations?
, -> silent: only changes the base at the end of the codon is changed ( no change to amino acid )
-> nonsense: causes a premature stop codon , only changes the base at the front codon
-> missense: changes the middle base in codon.
What are insertions and deletions?
When a nucleotide pair is lost or gained in a gene, causing a frameshift.
What are rearrangements?
When pieces of chromosomes are missing, duplicated (there are extra copies), or moved around
What are the different types of DNA repair mechanisms?
Direct reversal of DNA damage, excision repair, double stranded break repair
Name an example of direct reversal of DNA.
Photolyase (an enzymes) reversing pyrimidine dimers
What are the key steps of photolyase reversing the DNA?
1. Photolyase recognizes dimers.
2. Energy from visible light is used by photolyase to break (remove) the cyclobutene ring, linking the
bases. This process is called photo reactivation (reverses crosslinks).
What is the difference between gene knockout and gene knockdown?
Gene knockdown - temporary reduction of the expression of a gene.
Gene knockout - permanently getting rid of gene.
What methods are used for knockout and knockdown gene expression.
Gene editing is used for gene knockout by using CRISPR/ Cas 9 to modify DNA and completely get rid of
the gene.
RNA interference (RNAi) is used for gene knockdown at the mRNA level. siRNA or miRNA degrade or
inhibit the translation of specific messenger RNA molecules to knockdown the gene expression. (done
naturally )
What is FISH?
Fluorescence In Situ Hybridization.
Uses fluorescent nucleotides to make the chromosomes they want to look at light up.
What are the 4 main steps of FISH?
1. The cell needs to be fixed (pauses/freezes the cells). To do that formaldehyde is used to fix the cells
making the proteins inside the cell stick together. This makes it easier to analyze and study them.
2. A probe is designed by taking a DNA strand that's complementary to the chromosomal region of
