2 7.1 - dna structure hl
TRANSCRIPT
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DP Biology 11DP Biology 11Unit 7.1DNA Structure HL
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DNA StructureDNA Structure
Features of DNA double helixAntiparallel strands:
◦ The two strands have their 3’ and 5’ terminals at opposite ends
5’ - 3’ linkages◦ At one end of each DNA strand is a
phosphate group linked to carton atom 5 of deoxyribose
◦ At one end of each DNA is a hydroxyl group attached to carbon atom 3 of deoxyribose
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DNA StructureDNA Structure
Features of DNA double helixNucleotides linked by covalent
bonds◦ Between the 5’ phosphate group and the
3’ carbon atom of the other nucleotide
Hydrogen bonding◦ Between purines and pyrimidines
A purine can only bond with a pyrimidine and vice versa
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DNA StructureDNA Structure
Features of DNA double helixNitrogenous base
◦ Pyrimadines A one-ring structure (CUT the pie!) Cytosine, Thymine, and Uracil
U replaces T in RNA
◦ Purines A two-ring structure Guanine and Adenine
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DNA StructureDNA Structure
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DNA StructureDNA Structure
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DNA StructureDNA Structure
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DNA StructureDNA Structure
Nucleosome structureGrooves on the diameter of the
double helix◦ Expose compounds that can hydrogen
bond◦ Thus, DNA is bonded to proteins, called
histones
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DNA StructureDNA Structure
Nucleosome structureHistone proteins:
◦Eight histone proteins fit together perfectly 4 types, 2 of each type DNA wraps around this core twice
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DNA StructureDNA Structure
Nucleosome structureHistone proteins:
◦1 histone protein outside each nucleosome Organizes and holds the nucleosome
together
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DNA StructureDNA Structure
Nucleosome structureNucleosome
◦A structure for coiling DNA by combining it with histone proteins
◦DNA is wrapped twice around each nucleosome
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DNA StructureDNA Structure
Nucleosome structureNucleosome
◦DNA is wound around and hydrogen bonded to eight histones 146 DNA bases or 1.65 turns of the
helix are associated with the 8 histones
◦The combination of DNA and histones is secured by the 'H1 linker' protein 9 proteins total
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DNA StructureDNA Structure
Nucleosome structureNucleosome
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DNA StructureDNA Structure
SupercoilingUncoiled DNA is around 1.8 meters
long◦ Coiled to be moved around the cell
during mitosis◦ Partially uncoiled during transcription
◦ Nucleosomes aid in both these actions
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DNA StructureDNA StructureSupercoilingFor mitosis, DNA is coiled16,000x
◦DNA wraps twice around a histone proteins
◦These nucleosomes wrap around each other
◦These strands wrap around each other forming coils
◦These stack one upon another in a coil
◦= supercoiling
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DNA StructureDNA Structure
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DNA StructureDNA Structure
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DNA StructureDNA Structure
Single-copy vs. repetitive nuclear DNA
Unique or single-copy genes◦ Code for mRNA which codes for
polypeptides Around 25,000 different proteins
◦ About 1.5 % of our DNA
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DNA StructureDNA StructureSingle-copy vs. repetitive nuclear DNAHighly repetitive sequences
◦ Also called satellite DNA◦ Constitute 5-45% of the genome◦ Sequences are 5-300 base pairs per repeat◦ May be repeated up to 10,000 times per
genome
◦ Function of repetitive DNA is not known◦ Repetitive sequences vary from person to
person Useful in DNA profiling
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DNA StructureDNA Structure
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DNA StructureDNA Structure
Eukaryotic DNA: Exons and Introns
Eukaryotic organisms have DNA which differs from prokaryotic organism◦ Have exons and introns
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DNA StructureDNA Structure
Eukaryotic DNA: Exons and IntronsExons:
◦ Regions of DNA that are translated into proteins
Introns: ◦ Non-coding regions within the gene◦ These are copied when the gene is
transcribed to produce pre-mRNA◦ The intron-RNA is edited out to form
mature mRNA
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DNA StructureDNA Structure
Eukaryotic DNA: Introns and Exons
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ANIMATION
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TOK QUESTION:TOK QUESTION:
Power of LABELS
Highly repetitive sequences were once classified as “junk DNA”, showing a degree
of confidence that it had no role.
To what extent do the labels and categories used in the pursuit of knowledge affect the
knowledge we obtain?
SEE: “Failed states” in Politics, “Tracking” in Education, “Bad students/kids” in Parenting and Schools, “Day names” in
Africa
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MAJOR SOURCESMAJOR SOURCESThank you to my favorite sources of information when making these lectures!
John Burrell (Bangkok, TH)
www.click4biology.info
Dave Ferguson (Kobe, JA)
http://canada.canacad.ac.jp/High/49
Stephen Taylor (Bandung, IN)
www.i-biology.net
Andrew Allott – Biology for the IB Diploma
C. J.Clegg – Biology for the IB Diploma
Weem, Talbot, Mayrhofer – Biology for the International Baccalaureate
Howard Hugh’s Medical Institute – www.hhmi.org/biointeractive
Mr. Hoye’s TOK Website – http://mrhoyestokwebsite.com
And all the contributors at www.YouTube.com