dpt i, lec 3
TRANSCRIPT
IN THE NAME OF ALLAH MOST BENEFICIAL, MOST
MERCIFUL
The Cell and its functions
Dr Sadia Amer
Learning Objectives• Organization of cell.• Physical structure of cell.
Organization of cell• A typical cell consists of: 1-Nucleus 2-Cytoplasm The nucleus is separated from
cytoplasm by nuclear membrane. The cytoplasm is separated from
surrounding fluid by cell membrane or plasma membrane.
• The different substances that make up the cell are collectively called Protoplasm.
• Protoplasm has five basic substances:-WaterElectrolytesProteins Lipids Carbohydrates
Water• Principal fluid medium.• Present in all cells except fat cells.• About 75-80 % is water.• Many chemicals are dissolved in water.• Many are suspended as solid
particulate.
Electrolytes• Important ions are Na,K, Mg, PO4 ,
So4,HCO3, Cl, Ca.• Provide inorganic chemicals for
cellular reactions• Necessary for cellular control
mechanisms.
Proteins• Most abundant after water.• Constitute 10-20 % of cell mass.• Has two types: 1-Structural proteins 2-Functional proteins
Structural Proteins• Mainly in the form of long filaments
that are polymers of many individual protein molecules.• They form microtubules which
provide the “cytoskeletons” of organelles as cilia, nerve axons, the mitotic spindles etc
• Extracellularly, fibrillar proteins are found in collagen and elastic fibers of CT and in blood vessel walls, tendons, ligaments etc
Functional Proteins• Usually composed of combination of
few molecules in tubular-globular form.• These are mainly enzymes of cell.• Mobile in the cell fluid.• Some are adherent to membranous
structures inside the cell.
Lipids• Several Types of substances that are
grouped together because of their common property of being soluble in fat solvents are called lipids.• Constitute about 2% of total cell mass.• Examples:-phospholipids ,cholestrol
and triglycerides(neutral fat)
• Lipids are insoluble in water.• So used to form cell membrane and
intracellular membranes.• In fat cells , triglycerides constitute
about 95% of cell mass.• These are the body’s main store
house of energy giving nutrients.
Carbohydrates• Constitute about 1% of total cell mass.• 3% in muscle cell.• 6% in liver cells.• Present in cell as part of glycoprotein
molecule.• Play major role in nutrition of cell.
• Glucose is always present in ECF so that it is readily available when cell is in need.• Small amount of carbohydrate is
stored in cell in the form of glycogen.• Glycogen is an insoluble polymer of
glucose.
Physical structure of cell• The cell contains highly organized physical
structures called Intracellular organelles.• Most organelles are covered by
membranes called membranous organelles.
• Includes ER, Golgi apparatus, mitochondria, lysosomes, Peroxisomes
• These membranes are composed of lipids and proteins.• It provides barrier to movement of
water and water soluble substances.• Proteins provide channels as well as
act as enzymes.
Cell Membrane• Is thin, pliable, elastic structure .• About 7.5 to 10 nanometers thick.• Composed of lipids ,proteins. And carbohydrates.• Proteins=55%• Phospholipids=25%• Cholestrol=13%• Other lipids=4%• Carbohydrates=3%
Structure (LIPID)• It is a lipid bilayer, thin double
layered, each layer only one molecule thick.• Interspersed in this are large
globular protein molecules.
• Lipid bilayer is composed of phospholipids molecules.• Its one end is soluble in water i.e
hydrophilic.• Other end soluble in fats i.e
hydrophobic
• The phosphate end is hydrophilic and fatty acid portion is hydrophobic.• The lipid layer in the middle is
impermeable to water soluble substances e.g ions, glucose, urea etc
• Fat soluble substances like oxygen, carbon dioxide, alcohol etc can penetrates this portion.
• Cholestrol molecules in membrane are lipid in nature b/c their steroid nucleus is highly fat soluble.• They determine degree of
permeability.• It also control fluidity of membrane.
Cell Membrane Proteins
Cell membrane protein
• Two types of proteins are present:-Integral Protein
Peripheral Protein Integral proteins protrude all the
way through the membrane. Peripheral proteins are present to
only one surface of the membrane.
• Integral proteins provide structural channels through which water molecules and water soluble substances esp ions can diffuse.• These channels have selective
properties.• Some integral proteins act as carrier
proteins for transport of substances.
• Sometimes these even transport substances in direction opposite to their natural direction of diffusion.This is active transport.• Some act as enzymes.• Some serve as receptor for water
soluble chemicals e.g peptide hormone
• Peripheral proteins are often attached to integral proteins.• These act as enzymes or controllers
of transport of substances.
Membrane Carbohydrate• Occur in combination with proteins or lipids
in the form of glycoproteins or glycolipids.• The glyco portion protrude to outside of cell.• Proteoglycans are bound to small porotein
cores.• Entire outer surface is coated with Glycocalyx
Functions of carbohydrates• Give cell a negative surface.• Attaches cells to one another.• Some act as receptor substances for
binding hormones.• Some have role in immune
reactions .
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