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ZOOL 232 - CELL BIOLOGY
CELL - basic structural and functional unit of living organisms
CYTOLOGY - branch of biology dealing with study of cell structures how they function their interactions
with each other and their environment.
CELL HISTORY
1665 - Robert Hooke - discovered cells while observing thin slices of cork tissue obtained from tree bark,
it appeared to be made of many small compartments which were later called cells.
1676 - Anton Van Leeuwenhoek, observed animal tissue which he identified simple cells and called them
small animals "animalcules" he was the first to observe living cells e.g bone, sperm, bacteria and
protozoa.
1824 - Henri Miln Edwards - suggested the basic structure of all animal tissue as an array of globules
which are actually cells in modern terms.
Henri Durochet later proposed that the cell was not only a structural unit of life but also a phisiological
unit of living organisms, he also came up with the idea that cells originates from older ones, however,
Francoise Raspali was the first to discover that every cell is derived from another
1831 - Robert Brown discovered that cells contains a nucleus.
1832 - Barthelemy Dunlortier discovered binary fission ( type of cell division in plants) he came up with
the name tatalplasm to refer to material inside a cell.
Hogo Von Mohl is credited with discovering of cell division.
CELL THEORY
1838 - Mathias Schleiden - proposed that every structural element of plants is composed of cells or their
products
1939 - Theodor Schwann proposed that animals too are composed of cells or their products
Rudolf viuchous was the 1st to identify the nucleus role of controlling cell activities and that cells came
from preexisting ones
MODERN CELL THEORY
All living organisms are composed of one or more cells
A cell is a functional and structral unit of living organisms
Cells arises from preexisting ones through cell division
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Cells contains hereditary information that is passed from one cell to the other during cell division
All cells are basically same in chemical composition ( proteins, nucleic acids ...)
All energy flow of life occurs within cells (Biochemistry, metabolism)
TYPES OF CELLS
Prokaryotic
Eukaryotic
1. PROKARYOTIC
Lack a well defined nucleus, instead their genetic material lie naked in the cytoplasm in a region called
nucleoid.
Pro - meaning 'before' karyon - meaning ' spherical body'
It occurs in bacteria and archaea
They are usually small in size 1.1-1.5 * 2.0-6.0
Usually have single compartment without a defined nucleus
PARTS (8)
Cell wall, Glycocalyx, plasma membrane, cytoplasm, ribosomes, appendages, fimbriae, pili
1. CELL WALL
Made of complex molecule called peptidoglican ( combination of amino acids and disaccharide chains)
FUNCTIONS
Maintains cells shape
Provides support/ prevents bursting/ collapsing due to osmotic shock
Supports appendages like flagella (pilli)
2. GLYCOCALYX
A polysaccharide molecules layer that occurs on the outside of the cell wall.
Can occur in 2 forms . a) Capsule - compact/ hard
b) slime layer - diffuse form
FUNCTIONS
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Retain cells moisture
Protect cells from damage by other microorganisms/immune system/phagocytosis
Helps cells to stick to surfaces
Can act as food reserve
3. PLASMA MEMBRANE
Occurs beneath the cell wall, closes cells interior and regulates in and out flow of materials
4. CYTOPLASM
A gel like matrix composed of mainly water in which various substances are either dissolved or
suspended e.g nutrients enzymes and some organelles e.g ribosomes and plasmids
Within the cytoplasm theirs a nucleoid - a region that contains the DNA.
DNA is always circular and not associated with any proteins, it's involved in reproduction by carrying out
information necessary for cell division
In addition to DNA these Cells have plasmids which are extra chromosomal genetic materials made of
circular base of DNA
Plasmids aren't involved in reproduction, are exploited in biotechnology as vector to transport desired
genes into bacterial cells.
RIBOSOMES
Are composed of proteins and RNA, they are similar to those of eukaryotes except that they're smaller
FUNCTION
Site for protein synthesis
Contain different granules that functions as storage for nutrients
6. APPENDAGES
Composed of flagellum ( fimbriae) and pili
Flagella are long threadlike projections about 20nm*70nm in size. The core is a filament attachment to a
It's made up of several protofilaments, made of protein called flagellum
FUNCTIONS
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LOCOMOTION - where it rotates like a propeller to move the cell in a fluid medium.
May also serve as a sensory organelle for temperature and chemical stimuli
Can be involved in feeding mechanism by generating feeding currents in water to direct food towards
the cell
FIMBRIAE
Small hairlike projections that helps the cell to stick to one another and to other surfaces
PILLI
Projections that are long and hollow and are fewer in number and appear to be more rigid
FUNCTION
Attachment to surfaces and conjugation where they aid in transmission of genetic material between
cells
EUKARYOTIC CELL STRUCTURE
Much larger in size with a variety of internal membranes and organelles
1. CELL WALL
Present in plant cell and fungi
Composed of cellulose, hemicellulose and pectin in plants
Composed of chitin in fungi
FUNCTIONS
Provides support to the cell
Provides a filtering mechanism for substances
Protection to the cell components
Prevents cell destruction from osmotic shock
PLASMA MEMBRANE
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Present in all cells
Has a basic structure of proteins, lipids, carbohydrates...
FUNCTIONS
A cell boundary that encloses cell components
Regulates in and out movement of materials
Maintains cell shape
Enhances communication with other cells.
CYTOPLASMIC ORGANELLES
They are referred to as little organs
They are suspended in the cytoplasm
Each have a definite structure and specific function
All are membrane bound with some having two membranes around them
a) RIBOSOMES
Occurs in both Eukaryotic and PROKARYOTIC cells but differe in size 20nm, 25nm, they look alike and
perform same functions
They are manufactured by the nucleolus
Each consists of two components which are made separately in the nucleolus but they unite once they
arrive at the cytoplasm.
Larger subunit is 70s and 80s in prokaryotic and eukaryotic cells respectively and for the smaller subunit
60s and 40s
They may occur as free structures in the cytoplasm, as a group or cluster referred to as polysomes/
polyribosomes, bound to the ER to form RER as mitochondrial ribosomes
They bind to the ER under the influence of signal peptide
Most of the proteins made by free ribosomes functions within the cytoplasm while bound ribosomes
makes proteins destined for insertion in the plasma membrane and for carrying out specific roles in
organelles such as lysosomes, some of this proteins are for export from the cells, mitochondrial
ribosomes synthesizes mitochondrial proteins
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Made of RNA and proteins
FUNCTIONS
Protein synthesis
b) ER
A network of internal membranes extending through the cytoplasm
Are of 2 types RER and SER
RER has ribosomes studded on its surfaces
RER - packaging and transportation of proteins
SER - involved in lipid synthesis, detoxifying drugs, storage of calcium
Occurs in eukaryotic cells except RBCs and spermatozoa
They form network of membranes or tubules within the cytoplasm they're interconnected network of
flattened membrane bound sacks ( cisternae )
They have a lumen that is continuous and usually extend throughout the cytoplasm in most cells both
SER and RER have similar structures except for the ribosomes on the RER but they differe in functions
SER
Synthesis of lipids especially phospholipids and cholesterol for the cell membrane formation
They make estrogens and testosterone
They are abundant in cells that carry out excessive lipid synthesis e.g testis, ovaries, brain, sabaceous
galnds, intestines
Detoxifying drugs and poisons - occurs in kidney and liver cells and involves addition of hydroxyl groups
to drugs making them soluble and easily removable from the body, such drugs includes : sabaceous,
codcin, phenobarbital, alcohols, poisons e.g insecticides and carcinogens storage of calcium ions
especially within muscle Cells
Participates in the removal of phosphate groups from G-6-P in kidney, liver and intestinal cells allowing
free glucose to enter the bloodstream
RER
Synthesis and assemblying of proteins in association with ribosomes
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Most of these proteins are distined for exports from the cell such as digestive enzymes
Ribosomes forms a tight seal with the ER membrane and proteins enteres ER through the tunnel within
the ribosome that connects with the ER pore
In the ER lumen proteins are assembled and maybe modified by addition of lipids or carbohydrates
Glucose + proteins - glycosalation takes place partly in RER and partly in golgi
Packaged protein leave the RER wrapped in membrane vesicles, that bud off from a specialized region
called transitional ER, viscicles involved here are the transport vesicles
c) GOLGI COMPLEX
Made of stucks of membrane bound sacks and are involved in modification, packaging and sorting of
proteins and in formation of vesicles to transport substances within the cell
Consists of flattened membrane bound cisternae which are often curved, each of these has an internal
space or lumen and are about 40-100 stucks of cisternae in a mammalian cell
Each stuck consisting of 3 areas
a) Cis face ( Entry face )
b) Trans face ( Exit face)
c) medial region ( medial face)
CIS FACE
Cis face receives materials to be processed
It is usually convex and located near the nucleus and the faces of RER
It recieves materials mainly from the ER via transport vesicles
This materials fuse with the cisternae emptying their contents into the lumen of the golgi
Within the lumen of the golgi the materials are modified then sorted for transport within the medial
region
TRANS FACE
Faces the plasma membrane
Packages molecules into vesicles and transports them out of the golgi
VESICLES
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1. EXOCYTOTIC VESICLES
Directly released after being made
Contains proteins destined for extracellular release
E.g those found in B-cells that release antibodies
2. SECRETORY VISCICLES
Contains proteins destined for extracellular release but after packaging they are stored in the cell until
an approval signal is received for their release, then they move towards the plasma membrane, fuse
with it and release their contents
3. LYSOSOMAL VESICLES
Contains proteins and ribosomes destined for the lysosomes
4. SYNAPTIC VESICLES
They are located in the cis face, they carry materials involved in nerve transmission
5. TRANSFER VESICLES
Carry materials from golgi to various intracellular destinations
FUNCTIONS OF GOLGI
1. Synthesis of carbohydrates rich compounds e.g glycoproteins and mucopolysaccharides - to do this it
removes some sugar monomers and substitutes Others producing a large variety of carbohydrates
2. Formation of primary lysosomes - by budding from the golgi complex, contains hydrolytic enzymes
synthesized by RER and as they pass through the ER sugars are added identifying them as destined for
lysosomes
Primary lysosomes - not activated to work ( intracellular digestion)
3. Provides polysaccharide for the formation of cell wall in plants
4. Formation of achrosome of the sperm cell
5. Collagen biosynthesis
6. Modifies, sorts, packages, transports proteins recieved from RER
d) LYSOSOMES
Small spherical sacs found only in animal Cells
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Derived from golgi complex
Contain variety of hydrolytic enzymes
Are spherical vesicles, containing hydrolytic enzymes involved in breakdown of almost all biomolecules
surrounded by single unit membrane and is about 0.2 - 0.8 um in diameter though some can be as large
as 8um as in mammalian kidney cells and macrophages (WBC)
The enzymes are collectively called hydrolases because they work on addition of water molecules
They are present in all types of cells but plenty in leukocytes e.g macrophages and neutrophils
Primary lysosomes are newly formed and have not encountered the substrate on which to act on
Primary lysosome
- small in size
- sometimes called storage granules since they store enzymes
Secondary lysosomes
Formed by fusion of primary lysosomes with phagosomes ( phagocytic vesicles and also pinocytic
vesicles)
Carrying materials to be broken dowm
FUNCTIONS
Digestion of worn-out organelles and other unwanted material
Involved in cell death - apoptosis
Involved in intracellular digestion
Autophagy - involved in digesting selfcell contents or own organic material e.g unwanted organelles and
other cell structures - this is essential in the maintenance of balance between increase and decrease in
the number of cell population, this function occurs in response to nutrients starvation - during
neuralnatal period when the supply of nutrients via milk has not yet replaced nutrients via the placenta
2. House keeping process - recycling of the organelles
3. During erythrocytic dvpt - the nucleus is expelled by autophagic process and degradation of remaining
organelles e.g RBCs
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e) VACUOLES
They're membranous sacs
Common in plants, fungi and algae
Mainly for storage of waste material and other solids
Helps maintain hydrostatic pressure
f) PEROXISOMES
Small membranous sacs that contains a variety of enzymes
FUNCTIONS
Site for various metabolic reactions e.g breakdown of fatty acids and hydrogen peroxide
g) MITOCHONDRIA
Bounded by 2 membranes
Have a middle matrix
Involved in reaction that generate energy from glucose or lipids.
h) CHLOROPlAST
A double membrane structure with specialized membranes called thylakoids
Contain chlorophyll for photosynthesis
Present only in plant cell
I) CYTOSKELETON
Network of protein filaments
Composed of - microfilaments, microtubules, intermediate filaments
Microtubules are hollow while microfilaments are solid
Intermediate filaments are made of tough fibres
FUNCTIONS
Structural support to the cell
Enable cell and organelle movement
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Cell division - involved
Dividing the cell into compartments
As a component of cilia flagella and centrioles
j) NUCLEUS
Large, spherical bounded by 2 membranes which encloses the nucleoplasm (fluid), contains the
nucleolus and chromosomes
Nucleolus a body involved in synthesis and assembly of ribosomes
Chromosomes contains genes that structure and controls cells activity.

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ZOOL 232 - CELL BIOLOGY CELL - basic structural and functional unit of living organisms CYTOLOGY - branch of biology dealing with study of cell structures how they function their interactions with each other and their environment. CELL HISTORY 1665 - Robert Hooke - discovered cells while observing thin slices of cork tissue obtained from tree bark, it appeared to be made of many small compartments which were later called cells. 1676 - Anton Van Leeuwenhoek, observed animal tissue which he identified simple cells and called them small animals "animalcules" he was the first to observe living cells e.g bone, sperm, bacteria and protozoa. 1824 - Henri Miln Edwards - suggested the basic structure of all animal tissue as an array of globules which are actually cells in modern terms. Henri Durochet later proposed that the cell was not only a structural unit of life but also a phisiological unit of living organisms, he also came up with the idea that cells originates from older ones, however, Francoise Raspali was the first to discover that every cell is derived from another 1831 - Robert Brown discovered that cells contains a nucleus. 1832 - Barthelemy Dunlortier discovered binary fission ( type of cell division in plants) he came up with the name tatalplasm to refer to material inside a cell. Hogo Von Mohl is credited with discovering of cell division. CELL THEORY 1838 - Mathias Schleiden - proposed that every structural element of plants is composed of cells or their products 1939 - Theodor Schwann proposed that animals too are composed of cells or their products Rudolf viuchous was the 1st to identify the nucleus role of controlling cell activities and that cells came from preexisting ones MODERN CELL THEORY All living organisms are composed of one or more cells A cell is a functional and structral unit of living organisms Cells arises from preexisting ones through cell division Cells contains hereditary information that is passed from one cell to the other during cell division All cells are basically same in chemical composition ( proteins, nucleic acids ...) All energy flow of life occurs within cells (Biochemistry, metabolism) TYPES OF CELLS Prokaryotic Eukaryotic 1. PROKARYOTIC Lack a well defined nucleus, instead their genetic material lie naked in the cytoplasm in a region called nucleoid. Pro - meaning 'before' karyon - meaning ' spherical body' It occurs in bacteria and archaea They are usually small in size 1.1-1.5 * 2.0-6.0 Usually have single compartment without a defined nucleus PARTS (8) Cell wall, Glycocalyx, plasma membrane, cytoplasm, ribosomes, appendages, fimbriae, pili 1. CELL WALL Made of complex molecule called peptidoglican ( combination of amino acids and disaccharide chains) FUNCTIONS Maintains cells shape Provides support/ prevents bursting/ collapsing due to osmotic shock Supports appendages like flagella (pilli) 2. GLYCOCALYX A polysaccharide molecules layer that occurs on the outside of the cell wall. Can occur in 2 forms . a) Capsule - compact/ hard b) slime layer - diffuse form FUNCTIONS Retain cells moisture Protect cells from damage by other microorganisms/immune system/phagocytosis Helps cells to stick to surfaces Can act as food reserve 3. PLASMA MEMBRANE Occurs beneath the cell wall, closes cells interior and regulates in and out flow of materials 4. CYTOPLASM A gel like matrix composed of mainly water in which various substances are either dissolved or suspended e.g nutrients enzymes and some organelles e.g ribosomes and plasmids Within the cytoplasm theirs a nucleoid - a region that contains the DNA. DNA is always circular and not associated with any proteins, it's involved in reproduction by carrying out information necessary for cell division In addition to DNA these Cells have plasmids which are extra chromosomal genetic materials made of circular base of DNA Plasmids aren't involved in reproduction, are exploited in biotechnology as vector to transport desired genes into bacterial cells. RIBOSOMES Are composed of proteins and RNA, they are similar to those of eukaryotes except that they're smaller FUNCTION Site for protein synthesis Contain different granules that functions as storage for nutrients 6. APPENDAGES Composed of flagellum ( fimbriae) and pili Flagella are long threadlike projections about 20nm*70nm in size. The core is a filament attachment to a It's made up of several protofilaments, made of protein called flagellum FUNCTIONS LOCOMOTION - where it rotates like a propeller to move the cell in a fluid medium. May also serve as a sensory organelle for temperature and chemical stimuli Can be involved in feeding mechanism by generating feeding currents in water to direct food towards the cell FIMBRIAE Small hairlike projections that helps the cell to stick to one another and to other surfaces PILLI Projections that are long and hollow and are fewer in number and appear to be more rigid FUNCTION Attachment to surfaces and conjugation where they aid in transmission of genetic material between cells EUKARYOTIC CELL STRUCTURE Much larger in size with a variety of internal membranes and organelles 1. CELL WALL Present in plant cell and fungi Composed of cellulose, hemicellulose and pectin in plants Composed of chitin in fungi FUNCTIONS Provides support to the cell Provides a filtering mechanism for substances Protection to the cell components Prevents cell destruction from osmotic shock PLASMA MEMBRANE Present in all cells Has a basic structure of proteins, lipids, carbohydrates... FUNCTIONS A cell boundary that encloses cell components Regulates in and out movement of materials Maintains cell shape Enhances communication with other cells. CYTOPLASMIC ORGANELLES They are referred to as little organs They are suspended in the cytoplasm Each have a definite structure and specific function All are membrane bound with some having two membranes around them a) RIBOSOMES Occurs in both Eukaryotic and PROKARYOTIC cells but differe in size 20nm, 25nm, they look alike and perform same functions They are manufactured by the nucleolus Each consists of two components which are made separately in the nucleolus but they unite once they arrive at the cytoplasm. Larger subunit is 70s and 80s in prokaryotic and eukaryotic cells respectively and for the smaller subunit 60s and 40s They may occur as free structures in the cytoplasm, as a group or cluster referred to as polysomes/ polyribosomes, bound to the ER to form RER as mitochondrial ribosomes They bind to the ER under the influence of signal peptide Most of the proteins made by free ribosomes functions within the cytoplasm while bound ribosomes makes proteins destined for insertion in the plasma membrane and for carrying out specific roles in organelles such as lysosomes, some of this proteins are for export from the cells, mitochondrial ribosomes synthesizes mitochondrial proteins Made of RNA and proteins FUNCTIONS Protein synthesis b) ER A network of internal membranes extending through the cytoplasm Are of 2 types RER and SER RER has ribosomes studded on its surfaces RER - packaging and transportation of proteins SER - involved in lipid synthesis, detoxifying drugs, storage of calcium Occurs in eukaryotic cells except RBCs and spermatozoa They form network of membranes or tubules within the cytoplasm they're interconnected network of flattened membrane bound sacks ( cisternae ) They have a lumen that is continuous and usually extend throughout the cytoplasm in most cells both SER and RER have similar structures except for the ribosomes on the RER but they differe in functions SER Synthesis of lipids especially phospholipids and cholesterol for the cell membrane formation They make estrogens and testosterone They are abundant in cells that carry out excessive lipid synthesis e.g testis, ovaries, brain, sabaceous galnds, intestines Detoxifying drugs and poisons - occurs in kidney and liver cells and involves addition of hydroxyl groups to drugs making them soluble and easily removable from the body, such drugs includes : sabaceous, codcin, phenobarbital, alcohols, poisons e.g insecticides and carcinogens storage of calcium ions especially within muscle Cells Participates in the removal of phosphate groups from G-6-P in kidney, liver and intestinal cells allowing free glucose to enter the bloodstream RER Synthesis and assemblying of proteins in association with ribosomes Most of these proteins are distined for exports from the cell such as digestive enzymes Ribosomes forms a tight seal with the ER membrane and proteins enteres ER through the tunnel within the ribosome that connects with the ER pore In the ER lumen proteins are assembled and maybe modified by addition of lipids or carbohydrates Glucose + proteins - glycosalation takes place partly in RER and partly in golgi Packaged protein leave the RER wrapped in membrane vesicles, that bud off from a specialized region called transitional ER, viscicles involved here are the transport vesicles c) GOLGI COMPLEX Made of stucks of membrane bound sacks and are involved in modification, packaging and sorting of proteins and in formation of vesicles to transport substances within the cell Consists of flattened membrane bound cisternae which are often curved, each of these has an internal space or lumen and are about 40-100 stucks of cisternae in a mammalian cell Each stuck consisting of 3 areas a) Cis face ( Entry face ) b) Trans face ( Exit face) c) medial region ( medial face) CIS FACE Cis face receives materials to be processed It is usually convex and located near the nucleus and the faces of RER It recieves materials mainly from the ER via transport vesicles This materials fuse with the cisternae emptying their contents into the lumen of the golgi Within the lumen of the golgi the materials are modified then sorted for transport within the medial region TRANS FACE Faces the plasma membrane Packages molecules into vesicles and transports them out of the golgi VESICLES 1. EXOCYTOTIC VESICLES Directly released after being made Contains proteins destined for extracellular release E.g those found in B-cells that release antibodies 2. SECRETORY VISCICLES Contains proteins destined for extracellular release but after packaging they are stored in the cell until an approval signal is received for their release, then they move towards the plasma membrane, fuse with it and release their contents 3. LYSOSOMAL VESICLES Contains proteins and ribosomes destined for the lysosomes 4. SYNAPTIC VESICLES They are located in the cis face, they carry materials involved in nerve transmission 5. TRANSFER VESICLES Carry materials from golgi to various intracellular destinations FUNCTIONS OF GOLGI 1. Synthesis of carbohydrates rich compounds e.g glycoproteins and mucopolysaccharides - to do this it removes some sugar monomers and substitutes Others producing a large variety of carbohydrates 2. Formation of primary lysosomes - by budding from the golgi complex, contains hydrolytic enzymes synthesized by RER and as they pass through the ER sugars are added identifying them as destined for lysosomes Primary lysosomes - not activated to work ( intracellular digestion) 3. Provides polysaccharide for the formation of cell wall in plants 4. Formation of achrosome of the sperm cell 5. Collagen biosynthesis 6. Modifies, sorts, packages, transports proteins recieved from RER d) LYSOSOMES Small spherical sacs found only in animal Cells Derived from golgi complex Contain variety of hydrolytic enzymes Are spherical vesicles, containing hydrolytic enzymes involved in breakdown of almost all biomolecules surrounded by single unit membrane and is about 0.2 - 0.8 um in diameter though some can be as large as 8um as in mammalian kidney cells and macrophages (WBC) The enzymes are collectively called hydrolases because they work on addition of water molecules They are present in all types of cells but plenty in leukocytes e.g macrophages and neutrophils Primary lysosomes are newly formed and have not encountered the substrate on which to act on Primary lysosome - small in size - sometimes called storage granules since they store enzymes Secondary lysosomes Formed by fusion of primary lysosomes with phagosomes ( phagocytic vesicles and also pinocytic vesicles) Carrying materials to be broken dowm FUNCTIONS Digestion of worn-out organelles and other unwanted material Involved in cell death - apoptosis Involved in intracellular digestion Autophagy - involved in digesting selfcell contents or own organic material e.g unwanted organelles and other cell structures - this is essential in the maintenance of balance between increase and decrease in the number of cell population, this function occurs in response to nutrients starvation - during neuralnatal period when the supply of nutrients via milk has not yet replaced nutrients via the placenta 2. House keeping process - recycling of the organelles 3. During erythrocytic dvpt - the nucleus is expelled by autophagic process and degradation of remaining organelles e.g RBCs e) VACUOLES They're membranous sacs Common in plants, fungi and algae Mainly for storage of waste material and other solids Helps maintain hydrostatic pressure f) PEROXISOMES Small membranous sacs that contains a variety of enzymes FUNCTIONS Site for various metabolic reactions e.g breakdown of fatty acids and hydrogen peroxide g) MITOCHONDRIA Bounded by 2 membranes Have a middle matrix Involved in reaction that generate energy from glucose or lipids. h) CHLOROPlAST A double membrane structure with specialized membranes called thylakoids Contain chlorophyll for photosynthesis Present only in plant cell I) CYTOSKELETON Network of protein filaments Composed of - microfilaments, microtubules, intermediate filaments Microtubules are hollow while microfilaments are solid Intermediate filaments are made of tough fibres FUNCTIONS Structural support to the cell Enable cell and organelle movement Cell division - involved Dividing the cell into compartments As a component of cilia flagella and centrioles j) NUCLEUS Large, spherical bounded by 2 membranes which encloses the nucleoplasm (fluid), contains the nucleolus and chromosomes Nucleolus a body involved in synthesis and assembly of ribosomes Chromosomes contains genes that structure and controls cells activity. 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