Lecture 5
Photosynthesis
and Main Roads
of Genetics
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What is Photosynthesis?
Photosynthesis the process by which plants use
the energy from sunlight to produce sugar.
The conversion of sunlight energy into chemical
energy, is associated with the actions of the
green pigment Chlorophyll.
6H2O + 6CO2 ----------> C6H12O6+ 6O2
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The chemical equation translates as:
Six molecules of water plus six molecules of carbon
dioxide produce one molecule of sugar plus six
molecules of oxygen.
Diagram of a typical plant,
showing the inputs and outputs
of the photosynthetic process
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Main roads of Genetics:
Structure of the gene:
DNA is formed of double helix according to
Watson and Kreig model.
Nucleotides are the structural unit of DNA.
Every nucleotide consists of:
1- Deoxyribose sugar
2- Phosphate group
3- Nitrogenous base
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The nitrogenous bases are of two types:
Purines (Adenine A or Guanine G)
Pyrimidines (Cytosine C, Thyamine T)
Adenine and Thyamine are connected by 2
hydrogen bonds A T
Cytosine and Guanine are connected by 3
hydrogen bonds C G
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Double helix
DNA wrapes
around proteins
The genetic material
(DNA) is found inside
the nucleus.
DNA wraps around
Protein to form
nucleosomes which
is the structural unit
of chromosomes.
nucleosomes
Chromosome
consists of 2
chromatids
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Cell Cycle
Cell cycle includes 2 steps
1- Interphase (G1, S, G2)
2- Mitosis
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Cell spend most of their lives in interphase.
Interphase includes 3 stages:
1-G1 (Gap 1)
Cell growing
2- S (synthesis)
DNA duplication
3- G2 (Gap2)
Cell growing and preparation of next cellular
division.
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The cell undergoes 2 types of divisions
1- Mitosis
2- Meiosis
Mitosis
► Mitosis occurs in somatic cells.
► It leads to the growth of living organisms.
► It involves one nuclear division
► It results in 2 genetically identical daughter
cells
► Both daughter cells are diploid (2n)
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Mitosis includes 4 stages:
1- Prophase
2- Metaphase
3- Anaphase
4- Telophase
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1- Prophase:
- Chromosomes condenses and become visible.
- Each chromosome consists of 2 sister chromatids.
- Nuclear membrane and nucleolus disappears.
- Spindle fibers extends between the 2 centrioles at
the opposite poles of the cell.
Early Prophase
Late Prophase
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2- Metaphase:
- Chromosomes line up along the equator
- Chromosomes attach to the spindle fibers
at the centromeres
Metaphase
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Anaphase:
Sister chromatids separate and move to
opposite poles of the cell
Early Anaphase
Late Anaphase
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4- Telophase:
- Nuclear membrane and nucleolus reform.
- Spindle fibers disappears
- Chromosomes becomes long thin filaments (chromatin)
Telophase
Daughter Cells
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Plant Mitosis -- Review
Interphase
Prophase
Metaphase
Anaphase
Telophase
Interphase
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