Chapt 06
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Transcript of Chapt 06
GENERAL BIOLOGY
SCHOOL OF MLTFACULTY OF HEALTH SCIENCE
PREPARED BY: MANEGA
HDL 121DNA REPLICATION & PROTEIN
SYNTHESIS
DNA REPLICATION & PROTEIN SYNTHESIS
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Learning Outcomes
After completing this lecture, students will be able to:
(a) Describe basic chemical substances in cell
(b) Explain physical & chemical characteristic of
the substances
(c) Understand & describe the physiological
functions
Topics© 2010 Cosmopoint
DNA REPLICATION & PROTEIN SYNTHESIS
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Topic Outlines
1.1. Basic Chemical Substances In Cell1.1.1 Characteristics1.1.2 Physical & chemical1.1.3 Physiological functions
© 2010 Cosmopoint
DNA REPLICATION & PROTEIN SYNTHESIS
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Nucleic acids
A macromolecule composed of chains of monomeric nucleotide (linked together)
Polynucleotides are formed via polymerisation of nucleotides Form polynucleotides by condensation with the formation of phosphodiester
bonds Composed of
(a) A base (purine or pirimidine)
Purines: Adenine, guanine which are double ring structures
Pirimidines: Cytosine, thymine & uracil are single ring structures
(b) A sugar (ribose & deoxyribose)
(c) A phosphate group
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1.1. Basic Chemical Substances In Cell
DNA REPLICATION & PROTEIN SYNTHESIS
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1.1. Basic Chemical Substances In Cell
DNA REPLICATION & PROTEIN SYNTHESIS
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In biochemistry, these molecules carry genetic information or form structures within cells
The most common nucleic acids are
(a) DNA
(b) RNA (including mRNA, tRNA & rRNA)
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1.1. Basic Chemical Substances In Cell
DNA REPLICATION & PROTEIN SYNTHESIS
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RNA Ribonucleic acid A close cousin of deoxyribonucleic acid (DNA) Polymer of ribonucleoside-phosphates. Its backbone is comprised of alternating ribose & phosphate
groups Contain ribose while DNA contains deoxyribose
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1.1. Basic Chemical Substances In Cell
DNA REPLICATION & PROTEIN SYNTHESIS
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Three major types:
(a) messenger RNA (mRNA) carries information about a protein sequence to the ribosomes, the protein synthesis factories in the cell
(b) transfer RNA (tRNA) is a small RNA chain that transfers a specific amino acid to a growing polypeptide chain at the ribosomal site of protein synthesis during translation
(c) ribosomal RNA (rRNA) & protein combine to form a nucleoprotein called a ribosome. The ribosome binds mRNA & carries out protein synthesis
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1.1. Basic Chemical Substances In Cell
DNA REPLICATION & PROTEIN SYNTHESIS
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1.1. Basic Chemical Substances In Cell
DNA REPLICATION & PROTEIN SYNTHESIS
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Functions
Plays several important roles in the processes of translating genetic information from deoxyribonucleic acid (DNA) into proteins
RNA acts as a messenger between DNA & the protein synthesis complexes known as ribosomes
RNA forms vital portions of ribosomes Serves as an essential carrier molecule for amino acids to be used
in protein synthesis
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1.1. Basic Chemical Substances In Cell
DNA REPLICATION & PROTEIN SYNTHESIS
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Differences between DNA & RNA
DNA RNA
Double strands of polynucleotide Single strand of polynucleotide
Bigger molecule of more than a million bases
Smaller molecule of less than 1000 bases
Entirely double helix strand Single &/or double helix of intra-strand
Pentose within is deoxyribose Pentose within is ribose
Bases consist of A, C, G and T Bases consist of A, C, G and U
The ratio of A + G : C + T = 1 : 1 The ratio of A + G : C + U = 1 : 1
Almost all DNA is found in nucleus Found in both nucleus & cytoplasm
Its amount is constant in all cells, gametes have half the amount
Its amount varies among cells & it can be altered change
Chemically stable Not so stable
Not being broken down, it exists forever
Can be broken down by enzymes
Only one type Three types: rRNA, tRNA & mRNA
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1.1. Basic Chemical Substances In Cell
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Introduction - DNA
Within the nucleus of every cell are long strings of DNA The code that holds all the information needed to make & control
every cell within a living organism. Nucleic acid that contains the genetic instructions used in the
development & functioning of all known living organisms. Functionally divided into genes. Within the molecule, it has specific sequence of bases. This sequence of bases codes for a specific sequence of amino
acids in a protein.
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1.1. DNA Replication
DNA REPLICATION & PROTEIN SYNTHESIS
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It consists of just a few kinds of atoms: carbon, hydrogen, oxygen, nitrogen & phosphorus
Combinations of these atoms form the sugar-phosphate backbone of the DNA @ the sides of the ladder
Other combinations of these atoms form the four bases: thymine (T), adenine (A), cytosine (C) & guanine (G).
These bases are the rungs of the DNA ladder. It takes two bases to form a rung – one for each side of the ladder
04/10/2023DML 202 General Biology & Human
Genetics (Chapter 11: DNA & Protein Synthesis)
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1.1. DNA Replication
DNA REPLICATION & PROTEIN SYNTHESIS
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DNA Replication Process in which a molecule of DNA forms 2 molecules
of identical ones that are also identical to the original one
Takes place in the nucleus during S
interphase i.e. occurs just before cell division
in both mitosis & meiosis Aim: Prepare another identical set of DNA molecules to
make identical sister
chromatids so that chromosome are formed
before cell division can occur
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1.1.1.Process Involved
DNA REPLICATION & PROTEIN SYNTHESIS
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1.1.1.Process Involved
DNA REPLICATION & PROTEIN SYNTHESIS
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1.1.1.Process Involved
Occurs in semi-conservative way as proved by the experiment of Meselson & Stahl
An uncoiling enzyme helicase initially catalyses the uncoiling of small parts of DNA & then proceeds to the whole DNA
Can proceed simultaneously in
several spots of a DNA molecule
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DNA REPLICATION & PROTEIN SYNTHESIS
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1.1.1.Process Involved
DNA REPLICATION & PROTEIN SYNTHESIS
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Protein
Large organic compounds made of amino acids arranged in a linear chain & joined together by peptide bonds between the carboxyl & amino groups of adjacent amino acid residues.
The sequence of amino acids in a protein is defined by a gene & encoded in the genetic code.
Genetic code: a system of representation in which a code of 3 bases in the DNA or RNA codes for an amino acid in the protein.
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1.2 Protein Definition
DNA REPLICATION & PROTEIN SYNTHESIS
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A primer RNA strand is added to the side of one DNA strand that acts as a template by the addition of nucleotide triphosphates forming the new DNA strand called leading strand
It is catalysed by the enzyme DNA polymerase that adds nucleotides to the 3’ end of DNA, so replication proceeds in 5’ to 3’ fashion in the growing new DNA strand
The bases on these nucleotides are very particular about what they connect to.
Cytosine (C) will pair to guanine (G); adenine (A) will pair to thymine (T)
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1.2 Protein Definition
DNA REPLICATION & PROTEIN SYNTHESIS
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However, the process is different in the other complementary strand called lagging strand of DNA that is bent by the enzyme polymerase & short strands called Okazaki fragments are formed also in 5’ to 3’ way
DNA ligase: enzyme to join the fragments formed to become continuous long complementary strand
Finally when the primer is removed by DNA polymerase, 2 identical strands of DNA are formed
Each contains one side of the original DNA & one side made of ‘new’ nucleotide
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1.2 Protein Definition
DNA REPLICATION & PROTEIN SYNTHESIS
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1.2 Protein Definition
DNA REPLICATION & PROTEIN SYNTHESIS
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Protein
Large organic compounds made of amino acids arranged in a linear chain & joined together by peptide bonds between the carboxyl & amino groups of adjacent amino acid residues.
The sequence of amino acids in a protein is defined by a gene & encoded in the genetic code.
Genetic code: a system of representation in which a code of 3 bases in the DNA or RNA codes for an amino acid in the protein.
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1.2 Protein Definition
DNA REPLICATION & PROTEIN SYNTHESIS
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1.2 Protein Definition
DNA REPLICATION & PROTEIN SYNTHESIS
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Protein SynthesisCan be divided into
(a) transcription(b) activation of amino acids
(c) translation
(d) formation of functional
protein
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1.2.1 Protein Synthesis (transcription and translation)
DNA REPLICATION & PROTEIN SYNTHESIS
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1.2.1 Protein Synthesis (transcription and translation)
DNA REPLICATION & PROTEIN SYNTHESIS
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1.2.1 Protein Synthesis (transcription and translation)
DNA REPLICATION & PROTEIN SYNTHESIS
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Translation
The sequence of bases in mRNA is translated to become a sequence of amino acids in a polypeptide
Initially, mRNA forms a complex with the subunits of ribosome Two sites, P and A are created on the surface of the ribosome with
the first & second codes of the mRNA in them respectively The ribosome binds to the mRNA at the start codon (AUG) Two suitable amino-acyl tRNAs are then attached to the P site & the
A site respectively each with its anti-codon complementary to that of the mRNA.
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1.2.1 Protein Synthesis (transcription and translation)
DNA REPLICATION & PROTEIN SYNTHESIS
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1.2.1 Protein Synthesis (transcription and translation)
DNA REPLICATION & PROTEIN SYNTHESIS
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1.2.1 Protein Synthesis (transcription and translation)
DNA REPLICATION & PROTEIN SYNTHESIS
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A peptide bond is formed between the two amino acids, which are brought close together.
The process is catalysed by a ligaseA relative movement occurs in which the 3rd code of
the mRNA is shifted to the A site & its 1st code is shifted out liberating the 1st tRNA & the 2nd code sits on the P site
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1.2.1 Protein Synthesis (transcription and translation)
DNA REPLICATION & PROTEIN SYNTHESIS
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Protein Synthesis
Purpose: create a polypeptide – a protein made out of a chain of amino acids
In a hair follicle cell, a protein called keratin is made. Many ribosomes can be working on a single strand of mRNA at once.
Is not a slow processA protein chain with 400 amino acids long can be
assembled in 20 seconds.
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1.2.1 Protein Synthesis (transcription and translation)
DNA REPLICATION & PROTEIN SYNTHESIS
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A peptide bond is formed between the 2nd & 3rd amino acid lengthening the polypeptide
Another relative movement occurs & the process is repeated with further lengthening of the polypeptide until the last code gets into A site
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1.2.1 Protein Synthesis (transcription and translation)
DNA REPLICATION & PROTEIN SYNTHESIS
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The last codon is a ‘nonsence’ codon (UAG, UAA & UGA) indicating a ‘full stop’. No amino acyl-tRNA can get into the A site. The final relative movement would liberate the completed polypeptide, mRNA, tRNA & the subunits of the ribosomes
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1.2.1 Protein Synthesis (transcription and translation)
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1.2.1 Protein Synthesis (transcription and translation)
DNA REPLICATION & PROTEIN SYNTHESIS
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DML 202 General Biology & Human Genetics (Chapter 11: DNA &
Protein Synthesis)35
1.2.1 Protein Synthesis (transcription and translation)
DNA REPLICATION & PROTEIN SYNTHESIS
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