BiomoleculesNucleic acids

Nucleic acids Are the genetic materials of all organisms

and determine inherited characteristics. The are two kinds of nucleic acids, DNA &

RNA. DNA is found in genes which are on

chromosomes and carries ‘instructions’ for assembly of specific proteins. RNA is also involved in this process (transcription and translation). We will study this in UNIT4.

DNAAll life on Earth has a common thread at the

molecular level – DNA { deoxyribonucleic acid}DNA is a large (macro) molecule made up of a

series of chemical building blocks called nucleotides.

A nucleotide is composed of a phosphate group, sugar and a nitrogen containing base.

DNA is organised into segments called GENES In these genes are triplets called ‘codons’ that

translate the nucleotide sequences into amino acids (protein)

Each NUCLEOTIDE is made of: A phosphate group A 5 carbon sugar (deoxyribose),

[ in any nucleotide a phosphate is attached to the 5’ carbon and the base to the 1’ carbon]

One of the 4 bases (A,G,C,T)

Nucleotides join together to form a polynucleotide chain. The two ends of the chain are different and are referred to as the 5’ & 3’. This makes the DNA double helix ‘antiparallel’.

Complementary Base Pairs

The 4 nitrogenous bases are: Adenine (A) - Purine type double ring structure Guanine (G) - Purine type double ring structure Thymine (T) - Pyrimidine type single ring structure Cytosine (C) - Pyrimidine type single ring structure

Of these bases only A can bond to T and only G can bond to C

DNA Structure

DNA may exist as a double-stranded helix.

Each strand is a polynucleotide.

Each nucleotide is made up of a deoxyribose sugar, a purine or pyrimidine base and a phosphate group.

Structure of NucleotidesThe chemical structure of nucleotides:

Symbolic form

Phosphate: Links neighboring sugars

Sugar: One of two types possible: ribose in RNA and deoxyribose in DNA

Base: Four types are possible in DNA: adenine, guanine, cytosine and thymine. RNA has the same except uracil replaces thymine.

NucleotidesThe building blocks of nucleic acids (DNA and RNA) comprise the following

components:

a sugar (ribose or deoxyribose)

a phosphate group

a base (four types for each of DNA and RNA)

BaseSugarPhosphate

Adenine

DNA & RNA Compared

Structural differences between DNA and RNA include:

DNA RNA

Strands Double Single

Sugar Deoxyribose Ribose

Bases Guanine Guanine

Cytosine Cytosine

Thymine Uracil

Adenine Adenine

Nucleotide Bases

The base component of nucleotides which comprise the genetic code.

Base component of a nucleotide

Always pair up with purines

PyrimidinesCytosine

• Single-ringed structures

Thymine•

Uracil

PurinesAdenine

• Double-ringed structures

Guanine• Always pair up with pyrimidines

Double strand formation

This occurs because of H-bonding between the base pairs as follows:

N

N

N

N O

N

N

N

N

O

H

H

H

H

H

GuanineCytosine

7

3

G C

N

N

N

N N

N

N

O

O

CH3

H

H

H

AdenineThymine

7

3

TA

Note number of H-bonds between each base pair.

Watson and Crick double helix: B type

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

Watson and Crick double helix: B type

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

The central DOGMA of Molecular Biology can be summarised in the form:

RNA (ribonucleic acid)RNA is a single nucleotide chain, similar to DNA

(double chain), but with the sugar ribose in place of deoxyribose and uracil (U) rather than thymine (T).

The bases G, C, T and A in DNA are transcribed respectively as C, G A and U in RNA.

There are three main forms of RNA: ribosomal(rRNA), messenger (mRNA) and transfer RNA (tRNA).

Synthesis of ProteinsHow are such a diverse range of proteins possible? The code for making a protein is found in your genes (on your DNA). This genetic code is copied onto a messenger RNA molecule. The mRNA code is read in multiples of 3 (a codon) by ribosomes which join amino acids together to form a polypeptide. This is known as gene expression.

G T A C T A

Chromosome

The order of bases in DNA is a code for making proteins. The code is read in groups of three

DNAGene

Cell machinery copies the code making an mRNA molecule. This moves into the cytoplasm.

Ribosomes read the code and accurately join Amino acids together to make a protein

AUGAGUAAAGGAGAAGAACUUUUCACUGGAUAM S E E LK G TF G

The protein folds to form its working shape

M

S EK G

E L TF G

M

S

E

K

GE L TF G

M

S

E

K

G

EL

TF

G

M

S

E

K

G

EL

TF

G

M

S

E

K

G

EL

T F

G

CELL

NUCLEUS

Gene Expression

M

S

E

K

G

EL

T F

G

T

G

M

S

E

K

G

EL

F

T

G

M

E

K

G

EL

FS

Proteomics Proteomics is the study of the proteome. The proteome is the entire complement of

proteins expressed by a genome, cell, tissue or organism.

More specifically, it is the expressed proteins at a given time point under defined conditions.

The term is a blend of proteins and genome.

A cellular proteome is the collection of proteins found in a particular cell type under a particular set of environmental conditions such as exposure to hormone stimulation.

It can also be useful to consider an organism's complete proteome, which can be conceptualized as the complete set of proteins from all of the various cellular proteomes. This is very roughly the protein equivalent of the genome.

Proteome The term "proteome" has also been used to

refer to the collection of proteins in certain sub-cellular biological systems.

For example, all of the proteins in a virus can be called a viral proteome.

The proteome is larger than the genome, especially in eukaryotes, in the sense that there are more proteins than genes.