Download What is a cell Cell is the basic living, structural and

What is a cell
Cell is the basic living, structural and functional unit of the body
The human body develops from a single cell called the zygote, which
results from the fusion of the ovum(Female egg cell) &
spermatozoon (Male germ cell)
What is a cell
Functions of membrane proteins
Branched carbohydrate molecules attached to the outside of some
membrane protein molecules give the cell its immunological identity.
They can act as specific receptors for hormones & other chemical
mesengers.
Some are enzymes.
Some are involved in transport across the membrane.
NUCLEUS
Largest structure in the cell.
Contains hereditary units of the cell, called genes
Double membrane called nuclear envelope separates the nucleus
from cytoplasm.
Nuclear pores in the envelope allow most ions & water soluble
molecules to shuttle between the nucleus & cytoplasm.
Ribosomes
Contain ribosomal RNA & several ribosomal proteins.
Structurally a ribosome consists of 2 subunits, one about half the size
of the other.
They are sites of protein synthesis.
Free ribosomes have no attachment to other organelles
Other ribosomes are attached to the cellular structure called
endoplasmic reticulum.
Endoplasmic Reticulum
System of membrane enclosed channels of varying shapes called
cisterns.
Rough ER ribosomes, smooth Er- no ribosomes
Provides surface area for many types of chemical reactions & various
products are transported from one portion of the cell to another via
ER.
Ribosomes attached to rough ER synthesize proteins that will be
secreted.
Smooth ER synthesize lipids & detoxifies a variety of chemicals
including alcohol, pesticides, carcinogens.
Golgi Complex
Stack of 4-6 disc shaped membrane enclosed cisterns.
Associated with cisterns are small Golgi Vesicles, which cluster along
expanded ends of the cisterns.
Golgi complex processes, sorts, packages, and delivers proteins and
lipids to the plasma membrane, lysosomes , and secretory vesicles.
Proteins & lipids destined for inclusion in the plasma membrane or
for use inside lysosomes also pass through the golgi complex.
Transport Through Golgi Apparatus
Lysosomes
 One type of secretory vesicles formed by golgi apparatus.
 Contains digestive enzymes that break down molecules (Eg.
DNA, RNA, Carbs, Proteins) inside the cell into smaller particles
that are either recycled or extruded from the cell as waste
material.
 Lysosomes in WBC’s contains enzymes that digest foreign
materials such as microbes
Mitochondria
Mitochondria
Generates ATP an energy rich molecule which are called the “power
houses” of the cell.
Mitochondria consists of two membranes.
Mitochondria
 Central cavity enclosed by the inner membrane & cristae =
matrix.
 They are involved in cellular respiration as enzymes required
for the process are located on the cristae.
 Cellular respiration occurs only if O2 is present
 It results in catabolism of nutrient molecules such as glucose to
generate ATP
Microfilaments
Tiny strands of protein that provide structural support and maintain
the characteristic shape of the cell.
Microtubules
Larger than microfilaments.
Involved in the movement of the cell and of organelles within the
cell, the movement of cilia & possibly the organization of proteins in
the plasma membrane.
Transport of substances across cell membranes
Passive processes
Mechanisms that move substances across a membrane without using
cellular energy (released by splitting ATP)
Simple Diffusion
Simple Diffusion
Random mixing of ions and molecules in a solution due to their
kinetic energy is called diffusion.
Concentration gradient: one area ions are highly concentrated than
the other & the difference in the concentration is known as the
gradient.
One two such areas are connected they cause movement of
ions/molecules from area of high conc to low conc called net
diffusion.
Point of even distribution is called equilibrium.
Osmosis
Osmosis
Osmotic pressure an important force in the movement of water
between various compartments of the body.
Normally osmotic pressure of the cytosol inside the cells is the same
as osmotic pressure of extracellular fluid outside, because the
osmotic pressure on both sides is equal the cell volume remains
relatively constant.
Filtration
Site of filtration is in the kidneys.
Blood pressure forces small molecules such as creatinine (a waste
product) through the plasma membrane of cell lining microscopic
blood vessels capillaries.
Filtered liquids enter kidneys, from there these harmful substances
to be filtered can be eliminated in the urine.
Facilated Diffusion
ATP is used only as a source of phosphate
ACTIVE PROCESSES:
Bulk Transport
Moves larger substances across plasma membrane
Phagocytosis (Cell Eating)
Pinocytosis (Cell Drinking)
Engulfed material is a tiny droplet of ECF rather than a solid, no
pseudopods formed.
Membrane folds inward, forming a pinocytic vessicle which allows
liquid to flow inward & then surrounds the liquid.
The vessicle then detaches from rest of the intact membrane.
Receptor Mediated Endocytosis
 Ligands may be cholestrol, iron & vitamins are needed for
chemical reactions that sustain life.
 Other ligands are either hormones that deliver messages to
cells so cells can respond in specific ways or waste products
that certain cells have the ability to break down.
I.
Legand to specific receptor plasma membrane folds in froms
endocytic vesicle.
II.
Merging of endocytic vesicles to form endosome.
III.
Endosome then separates from ligand.
IV.
Receptors move back to plasma membrane by exocytosis.
V.
Portion of endosome containing ingested material with a
lysosome & ingested material are broken down by digestive
enzymes.
Exocytosis
Important in nerve cells, which release their neurotransmitter
substances by this process.
Important in secretory cells, eg. Cells that secrete digestive enzymes
or protein hormones, such as insulin.
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