n ucleic a cids as biology by1. n ucleic a cids - m ade in the nucleus and slightly acidic long...
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NUCLEIC ACIDSAS BiologyBY1
NUCLEIC ACIDS - MADE IN THE NUCLEUS AND SLIGHTLY ACIDIC
Long molecules (polymers) made up of nucleotides
Linked by condensation reactions2 main types:
DNA = deoxyribonucleic acidRNA = ribonucleic acid
NUCLEOTIDES
Nucleotides consist of a:• Pentose sugar• Phosphate group• Nitrogen-containing base
• (purine or pyrimidine)
INTRODUCTION TO NUCLEOTIDESAll 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
FORMATION OF NUCLEOTIDES
DNA
Has deoxyribose as the sugarExists as a double helix of 2 chains
linked by H bonds between complementary bases
Contains the nucleotides:AdenineThymineCytosineGuanine
Figure 2.16
COMPLEMENTARY BASE PAIRING :
A bonds with T
C bonds with G
BASESThere are five bases, split into two types:
adenine (A) and guanine (G) are purine bases. A G
T U
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
IDENTIFYING BASES
BASE PAIRING RULES
FORMATION OF POLYNUCLEOTIDES
DNA STRUCTURE
Held by covalent bonds
DNA2 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
DETERMINING 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.
STRUCTURE OF DNA
HOW 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
STRUCTURE OF EUKARYOTIC CHROMOSOMES
RNA Has ribose as the
sugar Is single-strandedUracil 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
RIBOSOMAL RNA
•Makes up part of the ribosome – made in the nucleolus
mRNA strand
ribosome
TRANSFER RNA
nucleotides
amino acidattachment site
anticodon
•Found in the cytoplasm•Used to carry amino acids to the ribosome during protein synthesis
3’ end
5’ end
hydrogen bond
MESSENGER 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 REPLICATION
DNA REPLICATION•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 REPLICATION
•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
WHAT’S THE KEYWORD?
MULTIPLE-CHOICE QUIZ