N UCLEIC A CIDS AS Biology BY1

N UCLEIC A CIDS - M ADE IN THE NUCLEUS AND SLIGHTLY ACIDIC Long molecules (polymers) made up of nucleotides Linked by condensation reactions 2 main types: DNA = deoxyribonucleic acid RNA = ribonucleic acid

N UCLEOTIDES Nucleotides consist of a: Pentose sugar Phosphate group Nitrogen-containing base (purine or pyrimidine)

I NTRODUCTION TO NUCLEOTIDES All nucleotides contain the following three groups: In DNA the sugar is deoxyribose, whereas in RNA the sugar is ribose. a phosphate group a pentose sugar a nitrogen- containing base

F ORMATION OF NUCLEOTIDES

DNA Has deoxyribose as the sugar Exists as a double helix of 2 chains linked by H bonds between complementary bases Contains the nucleotides: Adenine Thymine Cytosine Guanine Figure 2.16

COMPLEMENTARY BASE PAIRING : A bonds with T C bonds with G

B ASES There are five bases, split into two types: adenine (A) and guanine (G) are purine bases. AG TU thymine (T), cytosine (C) and uracil (U) are pyrimidine bases. DNA contains A, G, T and C, whereas RNA contains A, G, U and C. C

I DENTIFYING BASES

B ASE PAIRING RULES

F ORMATION OF POLYNUCLEOTIDES

DNA S TRUCTURE Held by covalent bonds

DNA 2 major functions: 1. replication, in dividing cells 2. carrying the information for protein synthesis in all cells Replication allows accurate copying of DNA for cell division

D ETERMINING THE STRUCTURE OF DNA The double-stranded structure of DNA was determined in 1953 by the American biologist James Watson and the British physicist Francis Crick. X-ray diffraction studies by British biophysicist Rosalind Franklin strongly suggested that DNA was a helical structure. The Austrian chemist Erwin Chargraff had earlier showed that DNA contained a 1:1 ratio of pyrimidine:purine bases.

S TRUCTURE OF DNA

H OW IS DNA PACKAGED ? In eukaryotic cells: DNA is packaged as chromosomes in the nucleus In prokaryotic cells: DNA is loose in the cytoplasm – there are no histones or chromosomes. It is tightly coiled and folded so that all 2m can fit in the nucleus It is wrapped around proteins called histones DNA + Histones = chromatin

S TRUCTURE OF EUKARYOTIC CHROMOSOMES

RNA Has ribose as the sugar Is single-stranded Uracil replaces Adenine A can hydrogen bond with U C can hydrogen bond with G

RNA 3 types: Ribosomal (rRNA) Messenger (mRNA) Transfer (tRNA)

RNA is made by making a complementary copy of a section of the DNA DNA RNA

R IBOSOMAL RNA Makes up part of the ribosome – made in the nucleolus mRNA strand ribosome

T RANSFER RNA nucleotides amino acid attachment site anticodon Found in the cytoplasm Used to carry amino acids to the ribosome during protein synthesis 3’ end 5’ end hydrogen bond

M ESSENGER RNA Is a mobile copy of a gene that codes for a protein It moves out of the nucleus to the ribosome to act as a template for protein synthesis mRNA strand ribosome mRNA DNA

ATP – ADENOSINE TRIPHOSPHATE Has ribose sugar, adenine, and 3 phosphate groups (Has 2 extra phosphates on the adenine containing nucleotide

ATP Is made by condensation reactions (dehydration synthesis) Is broken by hydrolysis reaction to liberate useful energy for the cell

DNA R EPLICATION

Watson and Crick provided evidence that complementary base pairing was key to DNA’s ability to replicate The DNA ‘unzips’ as hydrogen bonds between base pairs are broken

DNA R EPLICATION New polynucleotide strands can then be synthesized using the originals as a template Replication allows accurate copying of the DNA for cell division ( mitosis and meiosis )

DNA REPLICATION

W HAT ’ S THE KEYWORD ?

M ULTIPLE - CHOICE QUIZ