Carbohydrates. Simple Carbohydrates sugars –monosaccharides – single sugars –disaccharides…
1.2 CARBOHYDRATES
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Transcript of 1.2 CARBOHYDRATES
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1.2 CARBOHYDRATES
1.4 PROTEINS
1.3 LIPIDS
1.5 NUCLEIC ACIDS
1.1 WATER
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1.5 NUCLEIC ACIDS
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1.5 Nucleic Acids (11/2 hours)
Objectives :
• Describe the structure of nucleotide as the basic composition of nucleic acid (DNA & RNA).
• Describe the structure of DNA based on the Watson & Crick Model.
• State the types and function of RNA.
• State the differences of DNA & RNA.
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NUCLEIC ACIDS
Structure of DNA
Differences ofDNA & RNA
Structure of nucleotide
Types & functionOf RNA
mRNA, rRNA, tRNA
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DNAdeoxyribonucleic
acid
RNAribonucleic
acid
• 2 types
• Complex organic molecules• Polynucleotides (polymers of nucleotides)
NUCLEIC ACIDS
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Monomers / basic composition of nucleic acids
Each nucleotide composed of:i. Phosphate group
ii. Pentose sugariii. Nitrogenous base
STRUCTURE OF NUCLEOTIDE
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(nitrogenous base)
STRUCTURE OF NUCLEOTIDE
phosphate group
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STRUCTURE OF NUCLEOTIDE
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A hydrogen atom attached
to its 2nd carbon
A hydroxyl group attached
to its 2nd carbon
Pentose sugar
Deoxyribose ( in DNA ) C5H10O4 Ribose ( in RNA ) C5H10O5
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Ring structures for the 2 pentose sugars
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*In a nucleotide :- phosphate group is joined to the 5th C of pentose- nitrogenous base is joined to the 1st C of pentose
STRUCTURE OF NUCLEOTIDE
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Nitrogenous base2 groups
pyrimidine purine
6-membered ring6-membered ring fused to a 5-membered ring
Cytosine
Thymine (in DNA)
Uracil (in RNA)
Adenine Guanine
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Nitrogenous base(a) Pyrimidines (Single ring)
(b) Purines (Double ring)
Cytosine (C) Thymine (T) in DNA Uracil (U) in RNA
Adenine (A) Guanine (G)
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• Nucleotides are combined by condensation reaction
• forming a polynucleotide (DNA or RNA)
FORMATION OF POLYNUCLEOTIDE
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• 2 nucleotides are joined by a phosphodiester bond - between a
phosphate group (of a nucleotide)
& the 3rd C in a pentose (of the other nucleotide)
FORMATION OF POLYNUCLEOTIDE
123
45
Phosphodiester bond
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• Forming a backbone with repeating sugar-phosphate units
• Breakdown of polynucleotide may occur by hydrolysis
FORMATION OF POLYNUCLEOTIDE
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Organic bases
Pentose sugars
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• Watson & Crick proposed the double helix model in 1953 for DNA
• 1 DNA molecule consists of 2 helical polynucleotide strands
• The pentose sugar: deoxyribose • The nucleotides in each strand
are joined by phosphodiester bonds
STRUCTURE OF DNA
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• Contains 4 types of organic bases:- adenine (A)- guanine (G)- cytosine (C)- thymine (T)
STRUCTURE OF DNA
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• Organic bases of each strand are paired in the interior of the helix
• The helix shape is maintained by H bonds between organic bases of opposite strands
STRUCTURE OF DNA
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• Organic bases of each strand are paired in the interior of the helix
• The helix shape is maintained by H bonds between organic bases of opposite strands
STRUCTURE OF DNA• The 2 strands must be
complementary to each other
• A must pair with T with 2 H bonds
• G must pair with C with 3 H bonds
• For a DNA, amount of A = T ; G = C
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Hydrogen bonds
Hydrogen bonds
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• The 2 strands must run in opposite directions (anti-parallel)~1 strand runs
5’ 3’ while another runs 3’ 5’
STRUCTURE OF DNA
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5’
5’
3’
3’
Sugar-phosphate backbone Sugar-phosphate backboneBase pairs
OH
OH
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The double helixThe helix is “right-handed”, curving up to right. The two strands are held together by hydrogen bonds (dotted lines) between the nitrogenous bases, which are paired in the interior of the double helix.
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• DNA functions as the hereditary genetic material
–as it consists of nucleotides with certain sequence of organic bases
IMPORTANCE OF DNA
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• Single stranded polynucleotide• Pentose sugar: ribose• Nitrogenous bases - Adenine (A)
- Guanine (G)
- Cytosine (C)
- Uracil (U)
RNA
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Organic base is uracil instead of thymine
Onenucleotide
RNA
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• 3 types of RNA :–Messenger RNA (mRNA)
–Ribosomal RNA (rRNA)
–Transfer RNA (tRNA)
TYPES OF RNA
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i. mRNA • it carries the genetic code transcript
(copied from DNA)• carries it from the nucleus to the site of
protein synthesis in the cytoplasm
TYPES & FUNCTION OF RNA
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Involvement of mRNA in protein synthesis
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ii. rRNA• manufactured in the nucleolus• forms the ribosomal subunits
(together with ribosomal proteins)
TYPES & FUNCTION OF RNA
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Involvement of rRNA in protein synthesis
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iii. tRNA
• smallest RNA molecules containing 75 - 80 nucleotides
• different tRNAs to transfer (carry) the different amino acids to a ribosome during protein synthesis
TYPES & FUNCTION OF RNA
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tRNA
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Involvement of tRNA in protein synthesis
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• Mainly functions in protein synthesis
• For certain virus, RNA may become the hereditary genetic material
FUNCTIONS OF RNA
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• number of polynucleotide strands• types of:
–pentose sugar–nitrogenous bases
• location in cells• chemical stability & existing • basic form• function • molecular mass• ratio of nitrogenous bases
DIFFERENCES OF DNA & RNA
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Differences between DNA and RNA DNA RNADouble stranded ?
Larger molecular mass ?
Deoxyribose as pentose sugar ?
Organic bases: A,T,C,G ?
Found mainly in nucleus Manufactured in nucleus but found throughout the cell
Chemically very stable Chemically unstable
Permanent Temporary existing
Only 1 basic form ?
Ratio of A to T & G to C is one Ratio of A to U & G to C varies
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SEMESTER 1SESSION 2009/2010
Question • Differentiate between RNA and DNA.
[10 marks]
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SESSION 1999/2000
Question
• Elaborate on the structure of DNA according to Watson and Crick.
[10 marks]
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References :
• Campbell, 8th edition• Solomon, 9th edition
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Next Topic….• 2.0 Cell Structure & Functions
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2.2 Plant & Animal Cells
2.4 Cell Transport
2.3 Cell Membrane & Organelles
2.5 Cells are grouped
into tissues
2.1 Prokaryotic & Eukaryotic
Cells