Lecture 5 Photosynthesis and Main Roads of Genetics 1

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. 6H 2 O + 6CO > C 6 H 12 O 6 + 6O 2 2

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 3

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 4

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 5

Double helix DNA wrapes around proteins nucleosomes Chromosome consists of 2 chromatids The genetic material (DNA) is found inside the nucleus. DNA wraps around Protein to form nucleosomes which is the structural unit of chromosomes. 6

Cell Cycle Cell cycle includes 2 steps 1- Interphase (G1, S, G2) 2- Mitosis 7

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. 8

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) 9

Mitosis includes 4 stages: 1- Prophase 2- Metaphase 3- Anaphase 4- Telophase 10

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 ProphaseLate Prophase 11

2- Metaphase: - Chromosomes line up along the equator - Chromosomes attach to the spindle fibers at the centromeres Metaphase 12

Anaphase: Sister chromatids separate and move to opposite poles of the cell Early AnaphaseLate Anaphase 13

4- Telophase: - Nuclear membrane and nucleolus reform. - Spindle fibers disappears - Chromosomes becomes long thin filaments (chromatin) TelophaseDaughter Cells 14

Prophase Interphase Anaphase Metaphase Interphase Telophase Plant Mitosis -- Review 15