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 and proteins

Protein synthesis

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 digestive enzymes

Intracellular digestion

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 semi-

fluid 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