Human genome sequence

DNA = DEOXYRIBONUCLEIC ACID RNA = RIBONUCLEIC ACID Strong acid hydrolyses DNA & RNA into 3 components: nitrogenous base (4 different ones) sugar phosphoric acid Mild acid hydrolyses DNA & RNA into 2 components: Nucleoside = base—sugar Nucleotide = base-sugar-phosphate DNA & RNA are polymers of nucleotides

NUCLEOTIDE structure: nitrogenous bases PURINE amino ADENINE — A keto (carbonyl) GUANINE — G amino

NUCLEOTIDE structure PYRIMIDINE CYTOSINE — C THYMINE — T URACIL— U amino keto (carbonyl) methyl keto (carbonyl)

First difference between DNA and RNA: DNA contains the bases A, G, C and T RNA contains the bases A, G, C and U

NUCLEOTIDE structure D-ribose (RNA) D-2-deoxyribose (DNA) 2. THE SUGARS — pentoses 1 2 4 3 5 D-ribose (RNA) 1 2 4 3 5 H D-2-deoxyribose (DNA)

Second difference between DNA and RNA: DNA contains 2-deoxyribose RNA contains ribose

NUCLEOTIDE structure pH 7 (H3PO4) (HPO42-) 3. PHOSPHORIC ACID Phosphate ion

NUCLEOSIDE = base—sugar adenine ribose DEOXYADENOSINE = adenine—deoxyribose deoxy H

Adenosine 5'-monophosphate NUCLEOTIDE structure Base—sugar—phosphate adenine ribose e.g. ADENOSINE Adenosine 5'-monophosphate (5'-AMP) 5'

NUCLEOSIDE numbering ' "Prime" mark: ' 6 5 4 3 2 1 ' "Prime" mark: ' The 3' and 5' positions are very important for understanding DNA and RNA structure and function 5 4 3 2 1

Adenosine 5'-monophosphate (5'-AMP) Adenosine 5'-diphosphate (5'-ADP) ribose adenine 5' Adenosine 5'-triphosphate (5'-ATP)

How are mononucleotides linked together to form the polymers DNA and RNA? 5' O 3' P - 3',5'-phosphodiester bond

POLARITY 5' O 3' A C Single-stranded polynucleotides have one free 5' end and one free 3' end — they exhibit POLARITY

DNA is a double helix

What information did Watson and Crick use in 1953 to arrive at their "double helix" structure for DNA? Studies of DNA hydrolysis showed that the repeating unit was a NUCLEOTIDE CHARGAFF's "rules" %A = %T %G = %C

%A = %T %G = %(C + 5-MeC) %G = %C Plants have a particularly high content of 5-MeC %A = %T %G = %(C + 5-MeC) %G = %C

5-methylCYTOSINE 6-methylADENINE Note that in addition to the bases A,G, C and T there are some minor bases found in DNA H NH 2 O N CH3 5-methylCYTOSINE H N HCH 3 6-methylADENINE prokaryotes and eukaryotes prokaryotes

Conclusion: DNA MUST be double-stranded X-ray diffraction patterns obtained by Wilkins, Franklin & Gosling showed: helical structure with repeats at 0.34 and 3.4 nm 2 nm wide phosphates on outside of structure Density of chain suggests the helix contains 2 strands Conclusion: DNA MUST be double-stranded

A G T C GC base pair AT base pair 3 H-bonds 2 H-bonds 1.08 nm N H O C

sugar-phosphate backbone Double helical DNA Major groove Minor groove 3.4 nm: One helical turn Base pairs "stacked" vertically in interior sugar-phosphate backbone 2 nm 0.34 nm 10 bp per turn

Both strands coiled round a common axis Strands are ANTIPARALLEL 5' 3' 5' 3' One runs 5' to 3' Other runs 3' to 5'

Watson & Crick solved the structure of DNA in 1953 "...A structure this pretty just had to exist." - James Watson in The Double Helix

The implications of the ‘Double Helix’ Based on the fact that DNA is the genetic material: Stable Faithful replication and propagation of life Two strands: one can form the template for DNA replication Faithful transmission of information to RNA One strand acts as template RNA then transfers information to proteins http://science.nhmccd.edu/biol/bio1int.htm

DNA replication

Protein Structure

R is a chemical group that varies in different amino acids. Amino acid structure N C O OH H R R is a chemical group that varies in different amino acids. C is central “chiral” carbon.

Non-polar amino acids

Polar amino acids

Peptide bonds result from dehydration of A.A.s

Primary structure is the sequence of A.A.s

Sickle-cell anemia cause

Secondary structure

Tertiary structure

Quaternary structure

If all cells come from other cells where did the first ‘life’ come from? The Miller-Urey experiment Water is heated in a closed apparatus containing methane (CH4), ammonia (NH3) and hydrogen (H2) and an electric discharge is passed through the mixture.

Many precursors can be produced in simple pre-biotic conditions Some amino acids found (building blocks for proteins) Some nucleic acids found e.g. adenine Some sugars found including ribose