- 30nm fibre (heterochromatin- genes not expressed)

L11- DNA introduction Flashcards by Saskia Chapman

DNA is found in the nucleus packaged into

chromosomes

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heterochromatin

condensed- darker

- genes not expressed

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euchromatin

uncondensed- light

- genes expressed

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DNA is made up of

genes

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central dogma

DNA–> RNA –> proteins

genes in the nucleus encode proteins found in the cytoplasm

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how many m of DNA in each cells and what’s its width

2m, 6um

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width of DNA helix

2nm

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linear DNA (DNA helix) is packaged first by

wrapping its self around histone core twice (nucleosome)

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nucleosome

histone with DNA wrapped around twice

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nucleosomes are linked by

linker DNA and look like beads on a screen

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beads on a screen

euchromatin

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beads on a string packaged tighter into

solenoid

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solenoid

30nm fibre (heterochromatin- genes not expressed)

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solenoids loops form to create

chromosomes

- no gene expression not accessible for transcription e

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one chromosome=

one DNA molecule

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one chromosome after replication

2 DNA molecules connected by a centromere

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end of chromosomes called

telomeres

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smaller arms

p arm

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longer arms

q arms

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a gene is a

stretch of DNA that codes for a protein

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genes are located on

the chromosomes in a fixed location

- diff genes have diff chromosomal locations

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how many genes carried on chromosomes

25,000

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how many pairs of chromosomes do humans have

23 pairs (sex chromosomes are a pair)
- 46 overall

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nucleic acid=

linear polymers of nucleotides (polynucleotides)

- negatively charged due to phosphate groups

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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

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