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Cellular Biology
Lesson Two
Cellular Biology
• Focuses on understanding living process at a
molecular level
• Cellular biology has opened up new
discoveries in genes responsible for cancer,
events regulating how a cell divides, and how
organisms develop from a single cell.
Learning focus
• Evaluate technological advances in the field of
cellular biology.
• Explain the roles of various organelles in
cellular processes
• Use appropriate terminology related to
biochemistry.
• Describe the structure of cell membranes
according to the fluid mosaic model and
explain the dynamics of the transport
mechanism
Introduction - Review
• All the molecules and atoms studied in lesson
one are not alive,
• The cell is alive
• What is a cell?
• What is the cell theory?
• Cell organelles and functions
Types of Cells
• Two types based on structure:
• Eukaryotic and Prokaryotic
Prokaryotic Cells
• Single –celled bacteria are the only cells that
are prokaryotic
• Bacteria are very diverse, some can
photosynthesis, others would not
• They have exterior cell wall, some have their
cell wall further surrounded by a capsule.
• some move with appendages called flagella.
• They have pili which help them attach to
various surfaces
Prokaryotic Cells
• No true nucleus
• Most of their genes are found in a single loop
of DNA, some have accessory rings of DNA
called Plasmids
• Photosynthetic bacteria have light sensitive
pigments contained in disks called thylakoids
• the cytoplasm contain granules called
ribosomes that carry out protein synthesis
Prokaryotic Anatomy of a bacteria
Eukaryotic Cells
• Eukaryotic cells include: algae, protozoa, fungi,
plants and animals
Name
Composition
function
Cell wall
Cellulose fibrils in plant cells
Support and protection
Plasma membrane
Phospholipid bilayer with embedded
protein
Passage of molecules in and
out of cell
Nucleus
Nuclear envelope surrounding the
nucleoplasm, chromosomes and
nucleoli
Cellular reproduction and
control or protein synthesis
Nucleolus
Concentrated area of chromatin, RNA Protein synthesis
and proteins
Ribosomes
Protein and RNA
Protein synthesis
Smooth endoplasmic
reticulum
Membranous flattened channels and
tubular canals without ribosomes
Various transport and/or
modification of proteins and
other substances, transport
by vesicle formation; lipid
synthesis in some cells
Rough endoplasmic
reticulum
Membranous flattened channels and
tubular canals studded with
ribosomes
Transport and/or
modification of proteins and
other substances, transport
by vesicle formation; protein
synthesis
Name
Composition
function
Golgi apparatus
Stack of membranous sacs in
animals
Processing and packaging
of molecules
Vacuoles/Vesicles
Membranous sacs in animal cells storage
Lysosome
Membranous vesicles containing Intracellular digestion
digestive enzymes
Microbodies
Membranous vesicle containing
specific enzymes
Various metabolic tasks
chloroplast
Double membrane layer in plant
cells
photosynthesis
mitochondrion
Double membrane layer
Cellular respiration
Cytoskeleton
Microtubules and
microfilaments
Shape of cell; movement of
its parts
Cilia and flagella
Microtubules in animal cells
Movement of cell
Centriole
Microtubules in animal cells
Forms basal bodies that
produces microtubules
Membrane Structure and Function
• Plasma membrane regulates the passage of
molecules in and out of the cell
• It is made up of a bilayer of phospholipids
The Fluid Mosaic Model
• Most acceptable model of the cell surface
• Proteins move about within a bed of semifluid lipids
• It was proposed by Singer and Nicolson in
1972
• And supported by electron micrographs
Fluid Mosaic Model of Cell Membrane
Description of the fluid mosaic model
• The phospholipid bilayer portion of the plasma membrane
forms a hydrophobic impermeable barrier
• Prevents the movement of polar molecules through the
membrane
• Cholesterol makes the membrane more impermeable to
biological molecules
• Charged molecules enter the cell through protein channels
• Glycolipids are cell makers peculiar to individual cells
• Glycolipids also regulate the action of plasma membrane
proteins involved in the growth of cell, and may be involved in
occurrence of cancer
• Glycoproteins also make cell to cell recognition possible
Movement of molecules across the
plasma membrane
• Selectively permeable:
– Diffusion
– Osmosis
– Concentration gradients
– Types of solutions : isotonic, hypotonic, hypertonic
– Turgor pressure, lysis, plasmolysis, crenation,
flaccid
Concentration gradient of Animals and Plants Cells
Transport by Carriers
• Transport proteins help biological molecules
that are unable to diffuse across the plasma
membrane get into the cell.
• They are very specific and can only bind with
certain molecules
– Facilitated transport – happens when a carrier
protein is used to assist in the movement of a
molecule across the plasma membrane when the
molecule is moving down its concentration
gradient, the process does not require energy.
Passive Transport
Active Transport
• Molecules are using carrier proteins to go against
their concentration gradient, so movement is from
an area of low concentration to one of high
concentration.
• Process requires energy in the form of ATP.
• Protein carriers involved are called pumps
• Example of an active pump is the sodium-potassium
pump, which is important for the transmission of
nerve impulses
Primary/Secondary Active Transport
• A cellular process the uses ATP directly to move
molecules or ions from one side of a membrane to
the other is called primary active transport.
• E.g. Na+ - K+ pump in the nerve cell
• Secondary active transport uses electrochemical
gradient as a source of energy to transport
molecules or ions across a cell membrane
• E.g. hydrogen-sucrose pump
• A pump actively exports H+ against gradient usually
primary active transport, then H+ sucrose
symporter can use H+ gradient to transport sucrose
against a concentration gradient into the cell
Sodium Potassium Pump
Endocytosis and Exocytosis
• Used by molecules that are too large to diffuse
through the cell membrane or be transported by
protein carriers.
• Endocytosis is the transportation of molecules
through the cell membrane by vesicle formation.
• When material taken in is very large the process is
called phagocytosis (cell eating), when material is
very small is called pinocytosis or cell drinking
Receptor-mediated endocytosis
• In this process a receptor called ligand binds
with a specific nutrient molecule and joins at
the beginning of endocytosis to form what is
called coat pit.
• Exocytosis is opposite to endocytosis, a vesicle
fuses with the membrane, discharging its
contents outside of the cell.
Endocytosis