Mitosis vs Meiosis
Notes in GENERAL BIOLOGY 1
Sources:Kto12 (PERCDC)
-----CHAPTER 1: CELL----At the end of each the topic the learners will be able to understand the:
1. Principles of the cell theory
2. Structures and functions of cell
3. Difference between prokaryotic & eukaryotic
4. Different cell types
5. Cell modification
6. Phases of the cell cycle
7. Importance of Mitosis and Meiosis
8. Transport mechanisms in cells
9. Difference between exocytosis& endocytosis
CELL - structural & functional units of living body.
- it is the smallest structure that is able to carry out the basic functions of life.
HOW WERE CELLS DISCOVERED?
• ROBERT HOOKE first discovered cell while viewing cork specimen. He noticed little rooms that resembled cells, & thus the term
"CELL" was born. Hooke was not able to observe living cells but they were remnants of a cell specifically the cell wall.
• ANTON VAN LEEUWENHOEK invention of a much better microscope led to the study of living cells.
The following years, other scientists also studied living cells. Their collective work led to the formulation of the CELL THEORY.
WHAT DOES THE CELL THEORY STATE?
a. All organisms are composed of one or more cells.
b. Cell is the structural unit of all living organisms.
• MATTIAS SCHLEIDEN proposed that all plants are composed of cells. The following year, THEODORE SCHWAN made a similar
statement regarding animals.
a. Cells come from pre-existing cells.
• RUDOLPH VIRCHOW showed that cells self reproduce which contributed to the third principle of the cell theory.
WHAT'S INSIDE A CELL?
Cell is made up of organelles, structures with a membrane that perform a variety of functions such as protein production,
storage of materials, harvesting energy & digestion of substance, & among others. Organelles roles are interdependent.
WHAT ARE THE FUNCTIONS OF THE ORGANELLES?
a. ENDOMEMBRANE SYSTEM
• Rough Endoplasmic Reticulum
- filled with ribosomes, production of glycoprotein.
• Smooth Endoplasmic Reticulum
- lacks ribosomes, responsible for lipid and hormone production.
• Golgi Apparatus
- packaging center of the cell.
• Vacuole
- serve as storage of the cell.
• Lysosome
- contains digestive enzymes, organelle - recycling facility of an animal cell.
b. ENERGY RELATED ORGANELLES
• Chloroplast
- disk shaped that specialize in photosynthesis.
• Mitochondrion
- place of cell respiration & where most ATP is generated.
c. CYTOSKELETON
-system of interconnected protein filament.
• Actin Filaments
- provide structural support to plasma membrane & facilitate mov't of the cell.
• Intermediate Filaments
- provide structure to cell.
• Microtubules
- important during cell division.
WHAT ARE THE TWO MAIN GROUP OF CELLS?
Cells, based on the basis of nucleus are classified into two large groups:
1. PROKARYOTIC CELL (pro =early/primitive)
2. EUKARYOTIC CELL (eu=true karyon/nucleus)
PLANT CELL ORGANELLES
• Nucleus
• Nucleolus
• Mitochondria
• Plasma membrane
• Cytoplasm
• Vacuole
• Cell wall
• Chloroplast
• Starch granules
ANIMAL CELL ORGANELLES
• Nucleus
• Nucleolus
• Mitochondria
• Cytoplasm
• Vacuole
• Endoplasmic Reticulum
• Centriole
• Pinocyte
WHAT MAKES UP A TISSUE?
Tissue is a group of same or similar cells that perform a specific function in the body.
Two Major Types of Tissue
1. PLANT TISSUE
• Meristematic Tissue
• Primary Plant Tissue
2. ANIMAL TISSUE
• Epithelial Tissue - for protection & coverings.
• Connective Tissue - it connects.
• Nerve Tissue - for signal & supports.
• Muscle Tissue - for movements.
WHAT IS CELL MODIFICATION?
It is a features or structure of the cell that makes it different from another type of the cell that makes it different from another
type of cell & at the same time enables it to carry out unusual functions.
WHY DOES CELL MODIFICATION OCCUR?
Plant & animal cells are specialized to be able to carry out their tasks efficiently. They have particular adaptation to their
structure to suits its function.
WHAT IS CELL CYCLE?
Cell cycle is an orderly sequence of stages that takes place from the time an eukaryotic cell divides to the time the resulting
daughter also divides. Its two main parts are: INTERPHASE & M PHASE.
INTERPHASE is the longest stage of cell cycle. It has three stages:
a. G1, the first interval when the cell grows before DNA replication.
b. S, the time of DNA replication.
c. G2, the second interval when the cell prepares to divide.
M PHASE or Mitotic Phase, replicated DNA & cytoplasm divide to make two new diploid cells, both the same chromosome
number.
It involves CYTOKINESIS which is the splitting of the cytoplasm in two making two new cells.
CELL CYCLE CHECKPOINT
It is a stage where the cell examines internal & external cues & decides whether to go through with cell division or not.
THREE MAJOR CHECKPOINTS:
G1 Checkpoint
G2 Checkpoint
Spindle Checkpoint
WHAT IS MITOSIS AND MEIOSIS?
MITOSIS is a process of cell division in which a cell divides produces identical copies of itself. This process is important for growth
and repair of the body. (PMAT)
Importance of Mitosis
a. It ensures equal distribution of nucleus material down to each daughter cell.
b. Constancy of species is maintained by keeping a constant chromosome number of each daughter cell that is genetically
identical to the parent cell.
c. It restores wear & tear of the body tissues heals wounds & replaces damaged or lost organs through regeneration .
d. It is a means of asexual reproduction for some organisms.
e. Facilitates growth from a single fertilized egg to an individual with billions or trillions of cells.
FOUR MITOTIC STAGES
A. PROPHASE -chromosomes condense & organize nuclear membrane & nucleoli disapper, spindle apparatus assembled &
attached to centromeres of duplicated chromosomes.
B. METAPHASE -spindles line up duplicated chromosomes along equator of cell, one spindle to each half or chromatid of
duplicated chromosome.
C. ANAPHASE -centromere of each duplicated chromosome is separated and paired chromatids are pulled apart.
D. TELOPHASE -chromosomes uncoil; nucleoli reappear; cytokinesis occurs and two genetically identical daughter cell are
produced.
MEIOSIS is a kind of cell division exclusive to gametes or reproductive cell. This process reduces the number of chromosomes
from a diploid (2n) number to a haploid [n] number.
It occurs in two stages as a diploid nucleus cannot be split into a haploid nucleus in a single division. (Meiosis1 & Meiosis2)
Importance of Meiosis
a. It reduces the number of gametes in half which allows them to unite during fertilization without increasing the normal no. of
chromosome in the offspring.
b. It produces new chromosome combination in the gamete through the process of crossing over.
c. It promotes genetic diversity, which is essential for the survival of the population.
Stages of Meiosis
Meiosis 1
A. Prophase 1 -spindle microtubules become attached to them as the nuclear membrane breaks up.
B. Metaphase 1 -homologous chromosome pairs line up in the middle of the cell. The two chromosomes of each pair become
joined the microtubules at the opposite side of the cell.
C. Anaphase 1 - all of the homologous chromosome separate and move towards the spindle pole.
D. Telophase 1 -homologous chromosome pairs reach the spindle poles, nuclear membrane form around them & cytokinesis
follows to produce two cells
Meiosis 2
You may think of meiosis 2 as a process similar to mitosis except the chromosomes does not replicate before division.
A. Prophase 2 -the centrioles will duplicate & separate into two centrosomes. The nuclear membrane breaksdown & the spindle
apparatus forms.
B. Metaphase 2 -chromosomes which are still duplicated, are aligned in the middle of the cell (metaphase plate).
C. Anaphase 2 -sister chromatids of each chromosome separate & move towards the opposite poles.
D. Telophase 2 -nuclear membrane forms around each set of chromosomes & cytokinesis occur, producing 4 haploid daughter
cells.
WHAT IS CROSSING OVER & WHEN DOES IT HAPPEN?
Crossing over is the process that involves an exchange of genetic material between non sister chromatids during meiosis. It
occurs during the leptotene stahes of prophase 1.
HOW DOES CROSSING OVER HAPPEN?
Crossing over happens in prophase 1 when chromosomes condense. Each is drawn closer to its homologous partner, so that nonsister chromatids align along their length. The tight parallel orientation facilitates crossing over.
WHY DO CHROMOSOME CROSS OVER?
Crossing over greatly contributes to variations among individuals. Maternal & paternal genes get shuffles to introduce new allele
combinations which results in the combination of trairs among offspring.
Without crossing over an organism's offspring would just be cloned of themselves.
WHAT ARE THE TRANSPORT MECHANISMS IN CELL?
A. Passive Transport
1. Diffusion - movement from an area of high to low concentration.
2. Facilitated Diffusion - a permease, or membrane enzyme, carries substance.
3. Osmosis -diffusion across a semi-permeable membrane.
4. Bulk flow -mass movements of fluids affected by pressure & solutes.
B. Active Transport
1. Membrane Pumps -permeable used to move substance usually in the opposite direction of diffusion.
2. Endocytosis -materials are brought into cell via:
• Phagocytosis: SOLIDS (cell eating)
• Pinocytosis: LIQUIDS (cell drinking)
3. Exocytosis -expel materials from cell.
-----CHAPTER 2: BIOLOGICAL MOLECULES----Objectives:
At the end of each topic the learners will be able to understand the:
1. Role, structure & functions of Carbohydrates, Proteins, Lipids and Nucleic Acid.
2. Components of an enzyme
3.Factors that may affect the enzyme activity.
4. Oxidation / Reduction Reactions
WHAT IS BIOMOLECULE?
BIOMOLECULES are molecules that occur naturally in living organisms like carbohydrates, proteins, lipids and nucleic acid.
A. CARBOHYDRATES
Structures:
• Composed of Carbon, Hydrogen & Oxygen.
• Simple six carbon sugar (glucose) is called a monosaccharide.
• Two molecules or units join together to form disaccharide (sucrose).
• More than ten units of monosaccharides join in a chain to form a polysaccharide like starch and cellulose.
Functions:
• Most abundant organic substance present in nature which occurs in the form of cellulose in plant cell wall.
• In both plants and animals it is used as a source of energy (sugar).
• An important storage form in plants is starch and in animals it is glycogen.
• Present in Nucleic acid as five carbon sugar
(Ribose in RNA & Deoxyribose in DNA).
B. PROTEINS
Structures:
• Composed of Carbon, Hydrogen, Oxygen & Nitrogen.
• Amino acid join together by peptide bonds to form protein molecules.
• Twenty different amino acid make numerous simple & complex proteins.
• Based on the complexity of structure the proteins can have primary, secondary, tertiary & quaternary structures.
• When proteins exist with other molecules they are known ad conjugated proteins like glycoprotein, lipoprotein &
chromoprotein.
Functions:
• Structurally proteins from integral part of the membranes.
• Functionally in the form of enzymes they play a vital role in metabolic reactions.
• Synthesis of DNA is regulated by proteins (enzymes).
C. NUCLEIC ACID
Structure:
• They are of two types: DNA & RNA
• They are long chain polymers composed of units called NUCLEOTIDES as PURINES (Adenine & Guanine) and PYRIMIDINES
(Thymine, Cytosine & Uracil)
• Each nucleotide has pentose sugar, nitrogen base & phosphate group.
• DNA had one Oxygen less in its sugar molecule.
Functions:
• DNA is the main genetic material for almost all organisms except certain viruses.
• RNA molecules are involved in information transfer & protein synthesis; & RNA acts as genetic material in some viruses like
TMV (Tobacco Mosaic Virus).
D. LIPIDS
Structure:
• Composed of C, H, O. An amount of Oxygen is very less.
• They are synthesized from fatty acids and glycerol. Simple lipids are called glycerides.
• Fats can be saturated or unsaturated.
• Fats are solid at room temperature, those remain liquid at room temperature are called oils.
Functions:
• Due to their low oxygen content, & higher number of C-H bonds they store higher amount of energy & release more energy
during their oxidation.
• A molecule of fat can yield twice as much energy as from carbohydrate.
• Phospholipids are important components of cell membranes.
WHAT IS ENZYMES?
Enzymes are chemical catalysts & speed up chemical reactions.
They play an important role in all cellular reactions such as respiration, photosynthesis & many others.
They are globular proteins with a specific tertiary shape.
They are usually specific to only one reaction.
The part of the enzyme that acts as catalyst is called the ACTIVE SITE.
WHAT ARE THE COMPOSITION OF ENZYMES?
The composition of enzymes is based on two main components, namely:
1. PROTEINIC COMPONENT
Enzymes are protein in nature & the proteinic component of enzymes is called Apoenzyme.
2. NON PROTEINIC COMPONENT
Most of the enzymes need a non proteinic component for their activity, which is known as cofactor.
Without cofactor enzymes cannot show any enzymatic activity. In some enzymes the cofactor is simply metal ion or organic
molecules or ions.
WHAT ARE THE TYPES OF ENZYMES?
CLASSIFICATION OF ENZYMES
(Accdg. to the type of rexn catalyzed)
1. OXIDO REDUCTASES
-oxidation-reduction rexns
2. TRANSFERASES
-group trabsfer rexns
3. HYDROLASES
-hydrolysis rexns
4. LYASES
-removal or addition rexns
5. ISOMERASES
-isomerization rexns
6. LIGASES
-the joining to two molecules.
-condensation rexns.
WHAT ARE THE FACTORS THAT MAY AFFECT THE ACTIVITY OF AN ENZYME?
FACTORS AFFECTING AN ENZYME ACTIVITY
1. pH
Every enzyme has its own optimum pH at which it shows maximum activity.
2. TEMPERATURE
Most of the enzymes show maximum activity between 37°C to 50°C.
3. SUBSTRATE CONCENTRATION
ENZYME CONCENTRATION &
PRESENCE OF CERTAIN ION
OXIDATION-REDUCTION REACTIONS
OXIDATION is the loses of an electron by a molecule, atom or ion.
REDUCTION is the gain of an electron by a molecule, atom or ion.
LEO GER
Oxidized element is called reducing agent.
Reduced element is called oxidising agent.
Mg + Cl2 ----> MgCl2
Mg ---->Mg(2+) + 2e
Oxidised (lost 2 e)
Cl2 + 2e ---->2ClReduced (gained e)
MgCl2
1 atom of Mg Oxidation no. of +2
2 atoms of Cl Oxidation no. Of -1
(+2 x1) + (-1 ×2) = 0
----CHAPTER 3: ENERGY TRANSFORMATION---Objectives:
At the end of each topic the learners will be able to understand the:
1. ATP-ADP Cycle
2. Photosynthesis: Light & Dark Reactions
3. Respiration: Aerobic and Anaerobic
THE SUN
Organisms must use the Sun's energy directly or indirectly to become and remain in an organized state.
WHAT IS METABOLISM?
It is a series of chemical reactions involved in storing (ANABOLISM) or releasing (CATABOLISM) energy.
WHAT IS ATP?
ATP or adenosine triphosphate is a high energy molecule with three phosphate. Energy stored in ATP is released by breaking
phosphate-to-phosphate bonds and creating ADP (with two phosphate) or AMP (with one phosphate).
ATP is recycled by adding back phosphate groups using energy from the sun.
ATP-ADP Cycle
l-----------------------------------------------------------------l
A-P-P-P (ATP)------------energy release l
^l-----------------A-P-P (ADP) + P ----l
WHAT IS PHOTOSYNTHESIS?
It is a process by which plant convey light energy into chemical energy.
6 CO2+ 6 H2O ---> C6H1206 +6O2
Sunlight (radiant energy) is captured by chlorophyll and carotenoid photo sigments (found in cytoplasm in prokaryotes and
chloroplasts in eukaryotes) in two main steps:
A. Light-dependent reactions (LIGHT REXNS):
The captured light energy is transferred to electrons that come from H2O (water). Oxygen(O2) is a by-product.
B. Light-independent reactions (DARK REXNS):
Energized electrons are transferred to CO2 (reduction rexns) to form glucose (in the Cavin-Benson Cycle)
WHAT IS CELL RESPIRATION?
It is a process by which the chemical energy of food is converted to ATP.
C6H12O6 + 6 O2 ----> 6 CO2 + 6 H2O
Highly energized electrons stored temporarily in glucose are removed (oxidation rexns) in a step-wise fashion to maximise energy
capture at each step:
A. GLYCOLYSIS : Anaerobic ,without oxygen, process in cytoplasm in which glucose ,a 6 carbon cpd., is oxidized to 2 pyruvates
which are both 3 carbon chains.
B.KREBS CYCLE: Aerobic ,with oxygen, process that oxidizes pyruvates to carbondioxide.
C. CHEMIOSMOTIC PHOSPHORYLATION : The energized electrons released during the previous steps are used to concentrate
hydrogen ions in one area (of the cell membrane in prokaryotes; of the mitochondrion in eukaryotes) to create a chemical
gradient between positively & negatively charged ions. The potential energy resulting from this osmotic gradient is used to
resynthesis ATP from ADP & AMP. After electrons have been used, they must be transferred to oxygen (O2).