Topic 1 - Deoxyribonucleic Acid

DNA stores the genetic information for the production of protiens

In a eukatyote it is associated with histone protiens found within the nucleus

Naked DNA is also found in the Chloroplast and mitocondria

Prokaryotes contain a single circular chromosome within the nucleoid

A Naked Chromosone means it is not bound to any protien

In Eukaryotes DNA is stored as linear paired chromosomes

DNA Structure

The two strands are are joined together by pairs of bases to form a double helix

Deoxyribose (Sugar) and a Phosphate Group Bind on either sides of the pairs of bases

Nucleotide

Nucleotide Description

There are 4 possible bases with A bonding with T and C bonding with G

Adenine, Thynime, Cytosine and Guanine are the 4 bases

They bond based on the number of hydrogen bonds, for A and T that is 2 and for C and G that is 3

Each base is attached to a sugar which is attached to a phosphate groupe.

5’ and 3’ Ends

DNA groups have direction defined by the bound or unboud phosphate group

The 5’ end has an unbound/terminal phosphate group

The 3’ end has an unbound/terminal hydroxyl group

The strands run in opposite direction antiparralel.

Linkages go from 3 prime to 5 prime as they are aysmetrical.

Diagram displaying DNA structure

DNA is transcribed in the 3’ to 5’ direction of the template DNA

Transcribe means creating RNA to send protien codes from the DNA to the ribosome inorder to make protiens.


Purine and Pyrimade Bases

The nitrogenous bases can be wither puriens or pyrimide bases based off the structure

Purines (2 Ring)

Pyrimidine (1 Ring)

Adenine

Thymine

Guanine

Cytosine


Uracil


DNA vs RNA

  • DNA has dexyribose where as RNA has only ribose

  • RNA is single helix where as DNA is a double helix

  • In RNA uracil replaces Thymine

  • DNA is longer


Types of RNA

  1. Messenger RNA (mRNA) Template for Translation

  2. Ribosomal RNA (rRNA) component of ribosome as catalyst)

  3. Transfer RNA (tRNA) delivers Amino acids to ribosome - has 3 bases as an identifer called a condon


DNA Packing

In eukayotes DNA is bound to histone to form chromation.

It is wrapped around 8 histone protiens in an organised way to form a nucleosome.

Nuclesomes are losely packed during most of the cell phase.

Methylation causes nucleosomes to pack tightly, decreasing expression of the gene.

Acetylation results in losely packing, increasing gene expression.

Topoisomerase Enzymes causes DNA to supercoil

Why?

For organises DNA to fit inside the nuclues as well as for the DNA to stay organised in cell replication.


DNA Replication

DNA replication is the process by which DNA makes a copy of itself.

DNA replicates during Interphase (S-Phase) before mitosis and Meiosis.


Step 1. Unwind DNA

Completed by a helicase enzyme which breaks the hydrogen bonds.

Stage 2. Build daughter DNA strand

DNA polymerase adds complemantry bases.

The polymerase move from 3’ to 5’

Therefore strands grow from 5’→ 3’

Stage 3. Rewind

The new daughter DNA rewind into the doubele helic form.


DNA Replication is Semi-Conservative

  1. One Strand will be the original template

  2. The other strand will be the newly synthesized.


Multiple Replication Sites

Origin of replicatation occurs at multtiples points where the DNA comes unzziped and forms a replication fork moving in two directions.

Many sections of DNA can be replicated at once for speeding up the replication.


Contentious and Discontinuous

As polymerase run unidirectional it causes a lagging and leading strand.


Leading Strand:

Assembled continuously, starts replication from the 3’ end


Lagging Strand:

Broken up into (Okazaki) fragments later joined together by the ligase enzymes. Starts replication from the 3’ end.