L11- DNA introduction Flashcards
DNA is found in the nucleus packaged into
chromosomes
heterochromatin
condensed- darker
- genes not expressed
euchromatin
uncondensed- light
- genes expressed
DNA is made up of
genes
central dogma
DNA–> RNA –> proteins
genes in the nucleus encode proteins found in the cytoplasm
how many m of DNA in each cells and what’s its width
2m, 6um
width of DNA helix
2nm
linear DNA (DNA helix) is packaged first by
wrapping its self around histone core twice (nucleosome)
nucleosome
histone with DNA wrapped around twice
nucleosomes are linked by
linker DNA and look like beads on a screen
beads on a screen
euchromatin
beads on a string packaged tighter into
solenoid
solenoid
- 30nm fibre (heterochromatin- genes not expressed)
solenoids loops form to create
chromosomes
- no gene expression not accessible for transcription e
one chromosome=
one DNA molecule
one chromosome after replication
2 DNA molecules connected by a centromere
end of chromosomes called
telomeres
smaller arms
p arm
longer arms
q arms
a gene is a
stretch of DNA that codes for a protein
genes are located on
the chromosomes in a fixed location
- diff genes have diff chromosomal locations
how many genes carried on chromosomes
25,000
how many pairs of chromosomes do humans have
23 pairs (sex chromosomes are a pair) - 46 overall
nucleic acid=
linear polymers of nucleotides (polynucleotides)
- negatively charged due to phosphate groups
what makes up a nucleotide
base + sugar (phosphate). + phosphate
difference between ribonucleic and deoxyribonucleic acid
ribonucleotide has two hydroxyl group
deoxyribonucleotide has one hydroxyl group
ribonucleic acid
forms RNA
- ribose as sugar
deoxyribonucleic acid froms
DNA
- 2- deoxyribose as sugar
name the 4 bases
adenine
guanine
cytosine
thyrmine
two types of nitrogenous base
purine and pyrimidine
purine
adenine
guanine
pyrimidine
thymine
cytosine
uracil
nucleoside
base + sugar (without phosphate)
RNA adenine nucleoside
adenosine
RNA guanine nucleoside
guanosine
RNA uracil nucleoside
uridine
RNA cytosine nucleoside
cytidine
DNA adenine nucleoside
deoxyadenosine
DNA guanine nucleoside
deoxyguanosine
DNA thymine nucleoside
deoxythymidine
DNA cytosine nucleoside
deoxycytidine
RNA adenine nucleotide
adenosine monophosphate
RNA guanine nucleotide
guanosine monophosphate
RNA uracil nucleotide
uridine monophosphate
RNA cytosine nucleotide
cytidine monophosphate
DNA adenine nucleotide
deoxyadenosine monophosphate
DNA guanine nucleotide
deoxyguanosine monophosphate
DNA cytosine nucleotide
deoxycytosine monophosphate
DNA thymine nucleotide
deoxythymidine monophosphate
DNA and RNA run in the
5’ to 3’ direction
what are nucleotides joined together by
phosphodiester bonds
5’ end of DNA always has a
phosphate at the end
3’ end of DNA always has an
OH at the end
which parts of the nucleotides form hydrogen bonds
electronegative and electropositive sides
how many bonds between G-C
3 hydrogen bonds (strongest)
how many bonds between A- T and A-U
2 hydrogen bonds
DNA strands in the alpha helical structure run
anti-parallel
right handed
Minor and major grooves
order of cell cycle
Mitosis —>G1 —> Synthesis of DNA (replication) —> G2 —> Mitosis again
interphase includes
G1, S, G2
division
M
DNA replication is a ….. process
semi-conservative
- 1 strand of old and 1 new strand
DNA replication is catalysed by
DNA polymerase
- reaction driven by pyrophosphate hydrolysis
chain growth occurs from the
5’ to 3’
prokaryotes have different DNA to humans
naked circular chromosomes
outline DNA replication (simple)
- initiation
- elongation
- termination
detailed outline of DNA replication (prokaryotes)
1) DNA helices unwinds the DNA strand at origin of replication site
2) recruitment of DNA polymerase
3) primase produces primer which binds to single stranded DNA (Polymerase requires- can only add from 3’ end)
4) DNA polymerase elongates int he 5’ to 3’ direction
5) 3’ end of the DNA continuous replication
6) 5’ end will make strands in little fragments (Okazaki fragments)
7) helices continues to unwind double helix- moving the replication fork
8) termination- when replication forks meet each other and DNA ligase has joined everything
DNA replication in humans
many origins of replication
• Before replication: One chromosomes= 1 DNA molecules
• After replication: One chromosome = 2 DNA molecules
lagging strand
o 5’ end will make strands in little fragments- Okazaki fragments
leading strand
o continual replication