2 7.1 - dna structure hl
TRANSCRIPT
DP Biology 11DP Biology 11Unit 7.1DNA Structure HL
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
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
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
DNA StructureDNA Structure
DNA StructureDNA Structure
DNA StructureDNA Structure
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
DNA StructureDNA Structure
Nucleosome structureHistone proteins:
◦Eight histone proteins fit together perfectly 4 types, 2 of each type DNA wraps around this core twice
DNA StructureDNA Structure
Nucleosome structureHistone proteins:
◦1 histone protein outside each nucleosome Organizes and holds the nucleosome
together
DNA StructureDNA Structure
Nucleosome structureNucleosome
◦A structure for coiling DNA by combining it with histone proteins
◦DNA is wrapped twice around each nucleosome
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
DNA StructureDNA Structure
Nucleosome structureNucleosome
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
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
DNA StructureDNA Structure
DNA StructureDNA Structure
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
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
DNA StructureDNA Structure
DNA StructureDNA Structure
Eukaryotic DNA: Exons and Introns
Eukaryotic organisms have DNA which differs from prokaryotic organism◦ Have exons and introns
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
DNA StructureDNA Structure
Eukaryotic DNA: Introns and Exons
ANIMATION
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
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