BIOC0007 EXAM QUESTIONS AND ANSWERS WITH
COMPLETE SOLUTIONS VERIFIED LATEST UPDATE
Nucleotide vs nucleoside
- Nucleoside- glycosidic linkage of sugar and base
- Nucleotide- phosphoester linkage of phosphate to nucleoside
Purines
Adenine and Guanine
Pyrimidines
Cytosine and Thymine
Nitrogenous bases hydrogen bonding
- A-T: 2 H bonds
- C-G: 3 H bonds
Double helix conformation
- Two strands associated via H bonds and Van der Waals
- Antiparallel and complementary
- 2 strands make full 360 turn every 10.4bp
-ve supercoiled when condensed
-ve charged
- Major and minor grooves
A, B and Z DNA
,- A- less common, right handed, 26 A diameter (short and fat)
- B- most common (Watson Crick model), right handed, 20 A diameter
- Z- least common, left handed, 18 A diameter (tall and thin)
Prokaryotic genome packaging
- Single circular chromosome- nucleoid
- Condensed via Nucleoid Associated Proteins (NAPs), gyrase, Integration Host Factor
(IHF) (alpha and beta subunits)
Euchromatin
Light stained, relaxed (less condensed), transcriptionally active
Heterochromatin
Dark stained, compact, transcriptionally inactive
Nucleosome
- Basic unit of chromatin
- 147 bp of DNA around histone octamer
- 4 core histones
- +ve charged, Lys and Arg rich
Nucleosome formation into octamer
- H32-H42 tetramer + 2x H2A-H2B dimers
Levels of DNA packaging
- 10nm fibre, nucleosome association with linker (beads on a string)
- 30nm fibre- H1 linker histone bound to linker DNA, nucleosomes closer to each other
- H1 removed during transcription
Histone tails
,- N-terminus tails- H2A, H2B, H3, H4
- C-terminus tails- H2A, H2B
- 19-39 residues
- Extend from nucleosome complex
- Flexible and unstructured
- Chromatin remodelling
- Epigenetic regulation
Semi-conservative replication
Method of DNA replication in which parental strands separate, act as templates, and
produce molecules of DNA with one parental DNA strand and one new daughter DNA
strand
Meselson-Stahl Experiment
Used isotope of nitrogen to change the weight of DNA N15 & N14, demonstrated that
the semi-conservative model is the best description of replication.
Origin of replication
- Prokaryotes- oriC
- Eukaryotes- many ori
- DNA unwinds to form 2 replication forks moving in opposite directions, forming a
bubble
- Process is regulated to ensure replication occurs only once per cell cycle
- Origins 'fired' once replication beings so that they cant be used again until the next cell
cycle to prevent re-replication
, Initiator proteins
- DnaA in prokaryotes
- ORC in eukaryotes
- Bind to origin of replication
- DNA unwinds in AT rich region, recruit helicase
Helicase
- Hexameric ring shaped ATPase
- Breaks H bonds between DNA strands using energy from ATP hydrolysis
- DnaB in prokaryotes
- DnaC helicase loader
ssDNA binding proteins
- Prevents re-annealing of the separated single strands, protects against nuclease
degradation
- Single stranded binding protein (SSB) in prokaryotes
- Replication factor A (RPA) in eukaryotes
Primase
- DnaG in prokaryotes
- Part of MCM complex in eukaryotes
- Synthesises RNA primers as a starting point for DNA polymerase
- RNA primers degraded by nucleases, replaced by DNA
Topoisomerase
- Prokaryotes: DNA gyrase (introduces negative supercoils), Topo I
- Eukaryotes- Topo I, II
COMPLETE SOLUTIONS VERIFIED LATEST UPDATE
Nucleotide vs nucleoside
- Nucleoside- glycosidic linkage of sugar and base
- Nucleotide- phosphoester linkage of phosphate to nucleoside
Purines
Adenine and Guanine
Pyrimidines
Cytosine and Thymine
Nitrogenous bases hydrogen bonding
- A-T: 2 H bonds
- C-G: 3 H bonds
Double helix conformation
- Two strands associated via H bonds and Van der Waals
- Antiparallel and complementary
- 2 strands make full 360 turn every 10.4bp
-ve supercoiled when condensed
-ve charged
- Major and minor grooves
A, B and Z DNA
,- A- less common, right handed, 26 A diameter (short and fat)
- B- most common (Watson Crick model), right handed, 20 A diameter
- Z- least common, left handed, 18 A diameter (tall and thin)
Prokaryotic genome packaging
- Single circular chromosome- nucleoid
- Condensed via Nucleoid Associated Proteins (NAPs), gyrase, Integration Host Factor
(IHF) (alpha and beta subunits)
Euchromatin
Light stained, relaxed (less condensed), transcriptionally active
Heterochromatin
Dark stained, compact, transcriptionally inactive
Nucleosome
- Basic unit of chromatin
- 147 bp of DNA around histone octamer
- 4 core histones
- +ve charged, Lys and Arg rich
Nucleosome formation into octamer
- H32-H42 tetramer + 2x H2A-H2B dimers
Levels of DNA packaging
- 10nm fibre, nucleosome association with linker (beads on a string)
- 30nm fibre- H1 linker histone bound to linker DNA, nucleosomes closer to each other
- H1 removed during transcription
Histone tails
,- N-terminus tails- H2A, H2B, H3, H4
- C-terminus tails- H2A, H2B
- 19-39 residues
- Extend from nucleosome complex
- Flexible and unstructured
- Chromatin remodelling
- Epigenetic regulation
Semi-conservative replication
Method of DNA replication in which parental strands separate, act as templates, and
produce molecules of DNA with one parental DNA strand and one new daughter DNA
strand
Meselson-Stahl Experiment
Used isotope of nitrogen to change the weight of DNA N15 & N14, demonstrated that
the semi-conservative model is the best description of replication.
Origin of replication
- Prokaryotes- oriC
- Eukaryotes- many ori
- DNA unwinds to form 2 replication forks moving in opposite directions, forming a
bubble
- Process is regulated to ensure replication occurs only once per cell cycle
- Origins 'fired' once replication beings so that they cant be used again until the next cell
cycle to prevent re-replication
, Initiator proteins
- DnaA in prokaryotes
- ORC in eukaryotes
- Bind to origin of replication
- DNA unwinds in AT rich region, recruit helicase
Helicase
- Hexameric ring shaped ATPase
- Breaks H bonds between DNA strands using energy from ATP hydrolysis
- DnaB in prokaryotes
- DnaC helicase loader
ssDNA binding proteins
- Prevents re-annealing of the separated single strands, protects against nuclease
degradation
- Single stranded binding protein (SSB) in prokaryotes
- Replication factor A (RPA) in eukaryotes
Primase
- DnaG in prokaryotes
- Part of MCM complex in eukaryotes
- Synthesises RNA primers as a starting point for DNA polymerase
- RNA primers degraded by nucleases, replaced by DNA
Topoisomerase
- Prokaryotes: DNA gyrase (introduces negative supercoils), Topo I
- Eukaryotes- Topo I, II
