MOLECULAR BIOLOGY EXAM: LATEST A+ QUESTIONS
AND ANSWERS BREAKDOWN
building block of DNA
Deoxyribonucleoside 5' triphosphate (dNTP)
-N represents 1 of the 4 basic nucleosides
Sense strand of DNA
-non-template strand
Antisense strand of DNA
-template strand
nucleotides are built from 3 components
1) sugar (deoxyribose for DNA, ribose for RNA)
2) an aromatic, nitrogenous base
3) and 1-3 phosphate groups
purines
Adenine and Guanine
-they are derived from a precursor called purine
pyrimidines
Cytosine (C), Uracil (U), Thymine (T)
-CUT the Py
nucleoside
ribose or deoxyribose with a purine or pyrimidine linked to the 1' carbon
nucleotides
phosphate esters of nucleosides with 1, 2, or 3 phosphate groups joined to the ribose ring by
the 5' hydroxy group
backbone of DNA
sugar and phosphate
nucleotides in DNA chain are covalently linked by
,phosphodiester bonds between 3' hydroxy group of one deoxyribose and the 5' phosphate
group of the next deoxyribose
GC pair
held by 3 H bonds
AT pair
held by 2 H bonds
annealing
binding of 2 complementary strands of DNA into a double stranded structure
DNA double helix is stabilized by
van der Waal forces between the bases, which are stacked on each other
prokaryotic genomes
consist of a single, circular chromosome
viral genomes
may be linear or circular DNA or RNA
DNA gyrase
-if DNA remained as a simple double helix floating free in the cell, it would be fragile and bulky
-prokayrotes have a mechanism for making their single circular chromosome more compact
--DNA gyrase uses ATP to twist the large circular DNA molecule
---it functions by breaking the DNA and twisting the 2 sides of the circle around each other; the
twists are called supercoils
histones
globular proteins that eukaryotic DNA wraps around
nucleosomes
DNA wrapped around an octamer of histones
heterochromatin
DNA that is densely packed around histones. The genes in heterochromatin are generally
inaccessible to enzymes and are turned off.
Euchromatin
The less condensed form of eukaryotic chromatin that is available for transcription.
, centromere
region of chromosome to which spindle fibers attach during cell division
-the fibers attach via kinetochores: multi protein complexes that act as anchor attachment sites
for spindle fibers
chromosomes have 2 arms
p: short
q: long
telomeres
ends of linear chromosomes
-consists of repeated nucleotide sequences
-guanine rich DNA sequence
-composed of both single and double stranded DNA
-function to prevent chromosome deterioration and prevent fusion with neighboring
chromosomes
-prokaryotes do not contain telomeres since their genome is circular
intergenic regions of DNA
noncoding DNA
-may direct assembly of specific chromatin structures and can contribute to regulation of
nearby genes
-tandem repeats and transposons are major components of them
single nucleotide polymorphisms (SNPs)
Variations in the DNA sequence due to the change of a single nitrogenous base
-occur mostly in noncoding regions of genome
-some can lead to specific traits and phenotypes
tandem repeats
copies of genes repeated one after another along a chromosome
-repeats can be unstable when the repeating unit is short or if it's very long
--unstable tandem repeats can lead to chromosome breaks and can implicate disease
stop codons (aka nonsense codons)
UAA, UAG, UGA
- do not correspond to an amino acid
-notify ribosome that protein is complete and stop the reading of mRNA
synonym codons
AND ANSWERS BREAKDOWN
building block of DNA
Deoxyribonucleoside 5' triphosphate (dNTP)
-N represents 1 of the 4 basic nucleosides
Sense strand of DNA
-non-template strand
Antisense strand of DNA
-template strand
nucleotides are built from 3 components
1) sugar (deoxyribose for DNA, ribose for RNA)
2) an aromatic, nitrogenous base
3) and 1-3 phosphate groups
purines
Adenine and Guanine
-they are derived from a precursor called purine
pyrimidines
Cytosine (C), Uracil (U), Thymine (T)
-CUT the Py
nucleoside
ribose or deoxyribose with a purine or pyrimidine linked to the 1' carbon
nucleotides
phosphate esters of nucleosides with 1, 2, or 3 phosphate groups joined to the ribose ring by
the 5' hydroxy group
backbone of DNA
sugar and phosphate
nucleotides in DNA chain are covalently linked by
,phosphodiester bonds between 3' hydroxy group of one deoxyribose and the 5' phosphate
group of the next deoxyribose
GC pair
held by 3 H bonds
AT pair
held by 2 H bonds
annealing
binding of 2 complementary strands of DNA into a double stranded structure
DNA double helix is stabilized by
van der Waal forces between the bases, which are stacked on each other
prokaryotic genomes
consist of a single, circular chromosome
viral genomes
may be linear or circular DNA or RNA
DNA gyrase
-if DNA remained as a simple double helix floating free in the cell, it would be fragile and bulky
-prokayrotes have a mechanism for making their single circular chromosome more compact
--DNA gyrase uses ATP to twist the large circular DNA molecule
---it functions by breaking the DNA and twisting the 2 sides of the circle around each other; the
twists are called supercoils
histones
globular proteins that eukaryotic DNA wraps around
nucleosomes
DNA wrapped around an octamer of histones
heterochromatin
DNA that is densely packed around histones. The genes in heterochromatin are generally
inaccessible to enzymes and are turned off.
Euchromatin
The less condensed form of eukaryotic chromatin that is available for transcription.
, centromere
region of chromosome to which spindle fibers attach during cell division
-the fibers attach via kinetochores: multi protein complexes that act as anchor attachment sites
for spindle fibers
chromosomes have 2 arms
p: short
q: long
telomeres
ends of linear chromosomes
-consists of repeated nucleotide sequences
-guanine rich DNA sequence
-composed of both single and double stranded DNA
-function to prevent chromosome deterioration and prevent fusion with neighboring
chromosomes
-prokaryotes do not contain telomeres since their genome is circular
intergenic regions of DNA
noncoding DNA
-may direct assembly of specific chromatin structures and can contribute to regulation of
nearby genes
-tandem repeats and transposons are major components of them
single nucleotide polymorphisms (SNPs)
Variations in the DNA sequence due to the change of a single nitrogenous base
-occur mostly in noncoding regions of genome
-some can lead to specific traits and phenotypes
tandem repeats
copies of genes repeated one after another along a chromosome
-repeats can be unstable when the repeating unit is short or if it's very long
--unstable tandem repeats can lead to chromosome breaks and can implicate disease
stop codons (aka nonsense codons)
UAA, UAG, UGA
- do not correspond to an amino acid
-notify ribosome that protein is complete and stop the reading of mRNA
synonym codons
