Upload
lacy
View
45
Download
1
Tags:
Embed Size (px)
DESCRIPTION
1.2 CARBOHYDRATES. 1.1 WATER . 1.3 LIPIDS . MOLECULES OF LIFE. 1.5 NUCLEIC ACIDS . 1.4 PROTEINS . 1.5 NUCLEIC ACIDS. 1.5 Nucleic Acids (1 1 / 2 hours). Objectives : Describe the structure of nucleotide as the basic composition of nucleic acid (DNA & RNA). - PowerPoint PPT Presentation
Citation preview
1
1.2 CARBOHYDRATES
1.4 PROTEINS
1.3 LIPIDS
1.5 NUCLEIC ACIDS
1.1 WATER
2
1.5 NUCLEIC ACIDS
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.
NUCLEIC ACIDS
Structure of DNA
Differences ofDNA & RNA
Structure of nucleotide
Types & functionOf RNA
mRNA, rRNA, tRNA
DNAdeoxyribonucleic
acid
RNAribonucleic
acid
• 2 types
• Complex organic molecules• Polynucleotides (polymers of nucleotides)
NUCLEIC ACIDS
Monomers / basic composition of nucleic acids
Each nucleotide composed of:i. Phosphate group
ii. Pentose sugariii. Nitrogenous base
STRUCTURE OF NUCLEOTIDE
(nitrogenous base)
STRUCTURE OF NUCLEOTIDE
phosphate group
STRUCTURE OF NUCLEOTIDE
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
Ring structures for the 2 pentose sugars
*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
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
Nitrogenous base(a) Pyrimidines (Single ring)
(b) Purines (Double ring)
Cytosine (C) Thymine (T) in DNA Uracil (U) in RNA
Adenine (A) Guanine (G)
• Nucleotides are combined by condensation reaction
• forming a polynucleotide (DNA or RNA)
FORMATION OF POLYNUCLEOTIDE
• 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
• Forming a backbone with repeating sugar-phosphate units
• Breakdown of polynucleotide may occur by hydrolysis
FORMATION OF POLYNUCLEOTIDE
Organic bases
Pentose sugars
• 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
• Contains 4 types of organic bases:- adenine (A)- guanine (G)- cytosine (C)- thymine (T)
STRUCTURE OF DNA
• 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
• 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
Hydrogen bonds
Hydrogen bonds
• The 2 strands must run in opposite directions (anti-parallel)~1 strand runs
5’ 3’ while another runs 3’ 5’
STRUCTURE OF DNA
5’
5’
3’
3’
Sugar-phosphate backbone Sugar-phosphate backboneBase pairs
OH
OH
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.
• DNA functions as the hereditary genetic material
–as it consists of nucleotides with certain sequence of organic bases
IMPORTANCE OF DNA
• Single stranded polynucleotide• Pentose sugar: ribose• Nitrogenous bases - Adenine (A)
- Guanine (G)
- Cytosine (C)
- Uracil (U)
RNA
Organic base is uracil instead of thymine
Onenucleotide
RNA
• 3 types of RNA :–Messenger RNA (mRNA)
–Ribosomal RNA (rRNA)
–Transfer RNA (tRNA)
TYPES OF RNA
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
Involvement of mRNA in protein synthesis
ii. rRNA• manufactured in the nucleolus• forms the ribosomal subunits
(together with ribosomal proteins)
TYPES & FUNCTION OF RNA
Involvement of rRNA in protein synthesis
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
tRNA
Involvement of tRNA in protein synthesis
• Mainly functions in protein synthesis
• For certain virus, RNA may become the hereditary genetic material
FUNCTIONS OF RNA
• 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
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
SEMESTER 1SESSION 2009/2010
Question • Differentiate between RNA and DNA.
[10 marks]
SESSION 1999/2000
Question
• Elaborate on the structure of DNA according to Watson and Crick.
[10 marks]
References :
• Campbell, 8th edition• Solomon, 9th edition
Next Topic….• 2.0 Cell Structure & Functions
43
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