2 7.1 - dna structure hl

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


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


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





Nucleosome structureGrooves on the diameter of the

double helix◦ Expose compounds that can hydrogen

bond◦ Thus, DNA is bonded to proteins, called

histones


Nucleosome structureHistone proteins:

◦Eight histone proteins fit together perfectly 4 types, 2 of each type DNA wraps around this core twice


Nucleosome structureHistone proteins:

◦1 histone protein outside each nucleosome Organizes and holds the nucleosome

together


Nucleosome structureNucleosome

◦A structure for coiling DNA by combining it with histone proteins

◦DNA is wrapped twice around each nucleosome



◦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




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




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



Eukaryotic DNA: Exons and Introns

Eukaryotic organisms have DNA which differs from prokaryotic organism◦ Have exons and introns


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


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

Technology

2 7.1 - dna structure hl