Learning Objectives
- At the end of lecture student will be able to understand
- various
- Organelles
- Structure
- Function
Cytoplasm
- Fluid content present inside the cell membrane
- Contain dispersed particles and organelles
- Jelly-like fluid portion of cytoplasm in which particles are dispersed–cytosol
Endoplasmic Reticulum
- Interconnected network of tubular and vesicular structure in the cytoplasm
- Fluid filled system extending from nuclear membrane throughout the cytosol
- Space inside the tubules is called the endoplasmic matrix
Structure
Tiny interconnected tubules, arranged as stacks of flattened sacs
Consist of an outer membrane and inner matrix
MEMBRANE:
- Lipid bilayer with large amount of protein
- Inner limb of the membrane is continuous with the nuclear membrane, to connect with the nucleus.
Endoplasmic Reticulum
Types:
1.Agranularor Smooth endoplasmic reticulum
Lack ribosomes, NOT involved in protein synthesis
2.Granular or Rough endoplasmic reticulum
studded with small, dark-staining particles—Ribosomes
SER—FUNCTION
- Lipid synthesis and metabolism, further produce steroids and replace worn out part of membrane.
2 . Detoxification of harmful substances produce inside the body from metabolism or enter from outside like drugs etc. - Muscles have sarcoplasmic reticulum that stores calcium required for muscle contraction.
RER—FUNCTION
Rough endoplasmic reticulum synthesizes proteins, can serve for two purposes:
1.Transported as secretory vesicles to the cell’s exterior as hormones.
2.Helpful intracellularly in synthesizing the membranes and protein component of organelles.
Golgi Apparatus
- Membrane similar to that smooth ER
- Composed of 4 or more stacked layers of thin, flat, enclosed vesicles lying near one side of the nucleus
Functions
1.Formation of vesicles
◦Processing the ER secretions
◦Sorting and Directing the finished products to final destination
2.Synthetic Function
Golgi Apparatus
Processing of Endoplasmic Secretions and Transport
Endoplasmic reticulum(rough and smooth)
Synthesize proteins and lipids
Formed packed vesicles that buds of the er
Transport vesicles are formed
(Enclosed by membrane of endoplasmic reticulum)
Transported to golgi complex
Secretory vesicles are formed
(Containing protein and lipid substances)
Diffuse into the cell membrane
Fuse with it
Empty to the exterior of the cell
Process of exocytosis.
Lysosomes
- Vesicular organelles form by breaking off from the golgiapparatus
- Dispersed throughout the cytoplasm
- 250 to 750 nanometers in diameter.
- Provide an intracellular digestive system that allows cell to digest
- Damaged cellular structures
- Food particles that have been ingested by the cell
- Unwanted matter such as bacteria
- Lipid bilayer membrane, filled with large numbers of small granules 5 to 8nm in diameter
- Protein aggregates of different hydrolase (digestive) enzymes convert macro molecules to micromolecules
- Stores hydrolyticenzymes (Acid hydrolases)
- Phosphatases
- Nucleases
- Proteases
- Lipid-degrading enzymes
- Lysozymes digest bacteria
- Fuse with pinocytotic or phagocytoticvesicles to form digestive vesicles
Lysosomal Storage Diseases
- Absence of one or more hydrolases
- Not synthesized
- Inactive
- Not properly sorted and packaged
- Result: lysosomes become engorged with undigested substrate
- Examples:
- Acid lipase A deficiency
- I-cell disease (non-specific)
- Tay-sachsdisease (HEX A)
Peroxisomes
- Similar to lysosomes
- Self replicating
- Produce oxidases
- Detoxify alcohol with the help of oxidases
Secretory Vesicles
- Important cell functions is secretion of chemical substances
- Substances are formed by the endoplasmic reticulum–golgiapparatus system and are then released as storage vesicles called secretory vesicles or secretory granules.
- Store protein proenzymes(enzymes that are not yet activated)
Mitochondria
- Power house of the cell
- Produces energy and present in cytoplasm of almost all cells of the body
- Cardiac cells requires more activity than fat cells
- Vary in size and shape
- Diameter: From few hundred nanometers to 1 micrometer
- Can be globular or elongated in shape
Mitochondria
- Lipid bilayer with outer and inner membrane
- Inner membrane has shelves that contain oxidative enzymes
- Matrix between inner and outer membrane contain dissolved enzymes
- Oxidation of nutrients results in the formation of ATP
- Self replicating–contains DNA
- Exercising muscle increase density of mitochondria
Cytoskeleton
System of fibers that maintains the structure and allows change in shape of the cell
Network of fibrillary proteins arranged into filaments and tubules Made of
◦Microtubules
◦Intermediate filaments
◦Microfilaments
Microtubules
Structure with 5nm walls and cavity of 15nm
Three subunits alpha, beta and gamma
Provide tracks along with which molecular motors move various cell organelles
Present in flagellum of sperm
Intermediate Filaments
8-14nm in diameter
Connects cell membrane with nuclear membrane
Absorbs external pressure
Cell easily ruptures in absences of intermediate filaments
Microfilaments
4-6nm in diameter
Made of actin, involved in muscle contraction
F actin and G actin
G actin units polymerize to form F actin
Present in all cells of body
Molecular Motors
Three families of molecular motors:
◦Kinesin
◦Dynein
◦Myosin
Attach to cargo at one end of the molecule and to microtubule with the other end
Double headed structures
Classical example myosin bind to actin–muscle contraction
Vaults
RNA particles, octagonal in shape
3 times size of a ribosome
Also known as cellular trucks
Function unknown
Stick to nuclear pore cargo the molecules synthesize to elsewhere in the cell
Either vaults carry mRNA from nucleus to ribosomal sites of protein synthesis in the cytoplasm
Or vaults transport two subunits of ribosomes from the nucleus to their sites of action(RER or cytoplasm)
May cause drug resistance in cancer patients
Centrioles
Near the nucleus in the cytoplasm is a centrosome.
Composed of two centriolesand pericentriolarmaterial.
short cylinders arranged at right angles to each other
Three microtubules arranged longitudinally in the walls of each centriole
Nine of these triplets are arranged in a circle
When cell divides it duplicates and move to both the poles of cell
Nucleus
Control center of the cell
Message to cell to grow, mature, replicate and die
Contains DNA
Structural components
◦Nuclear Membrane
◦Nucleolus
◦Chromosomes
First cell division cell divides by mitosis and produce two identical daughter cells
Nuclear Membrane
Nuclear membrane –lipid bilayer
Outer membrane is continuous with ER
Several pores—9nm
Large enough to pass bigger particles
Nucleolus
Darkly stained large particle in the nucleus
Contains proteins and RNA
Enlarges during action (protein synthesis)
DNA forms RNA and that future get involved in protein synthesis
Transported from nucleus to cytoplasm
Transport
Exocytosis and endocytosis
Transport larger molecules such as proteins and polysaccharides,
and even very large particles.
Exocytosis
process in which material inside a cell is packaged into vesicles
and excreted into the extracellular medium
Endocytosis
Process in which the plasma membrane invaginatesor fold
inward, to form a vesicle that brings substances into the cell
Endocytosis
Takes large particulate matter into the cells
Three types
◦Phagocytosis
◦Pinocytosis
◦Receptor mediated endocytosis
Endocytosis
- Phagocytosis: or cellular eating, occurs when the dissolved materials enter the cell. The plasma membrane engulfs the solid material, forming a phagocytic vesicle.
- Pinocytosis: or cellular drinking, occurs when the plasma membrane folds inward to form a channel allowing dissolved substances to enter the cell. When the channel is closed, the liquid is encircled within a pinocyticvesicle.
- Receptor-mediated: chemical (LDL carrying cholesterol) binds to receptor protein before being brought into the cell
Pinocytosis
- Pinocytosis is the movement of liquid through the membrane of a cell
- “cell drinking,” the cell engulfs extracellular fluid, including molecules such as sugars and proteins
- Materials enter the cell inside a vesicle, although they do not mix with cytoplasm.
- Steps of Pinocytosis
- Formation of little vesicles that takes sips of extracellular fluid
- Membrane fold inward and small volumes of fluid are taken up
- Important for uptake of nutrients: cells in the digestive tract (particular intestine)
Phagocytosis
Receptor mediated endocytosis
Process by which cells internalize molecules or viruses
Depends on the interaction of molecule with a specific binding protein in the cell membrane called areceptor
Differs from the other two forms of endocytosis on the way of specificity
It’s a cellular lock and key
Receptor-mediated Endocytosis
Step 1 (Binding) : receptors in clathrin-coated pits bind with specific materials
Step 2 (invagination) : invagination of the plasma membrane occurs forming a clathrin-coated vesicle
Step 3 (uncoating) : the vesicle loses its clathrincoat and becomes an uncoated vesicle.
Step 4 (fusion) : the vesicle fuses with an endosome
Step 5 (recycling) : the vesicle divides and recycles the receptors to the plasma membrane via transport vesicles.
Step 6 (digestion) : another transport vesicle transports the ligands toward a lysosome; enzymes in the lysosome digest the ligands. The specific substances that attach to these receptor proteins actually have a specific name, called “ligands “.
Exocytosis
Exocytosis is similar to endocytosisbut in the opposite direction
Exocytosis steps: Five steps are involved in exocytosis
1.Vesicle Trafficking: In this first step, the vesicle containing the waste product or chemical transmitter is transported through thecytoplasmtowards the part of the cell from which it will be eliminated.
2.Vesicle Tethering As the vesicle approaches the cell membrane, it is secured and pulled towards the part of the cell from which it will be eliminated.
3.Vesicle Docking In this step, the vesicle comes in contact with the cell membrane, where it begins to chemical and physically merge with the proteins in the cell
4.Vesicle Priming: In the cells where chemical transmitters are being released, this step involves the chemical preparations for the last step of exocytosis.
5.Vesicle Fusion: last step, proteins forming the walls of the vesicle merge with the cell membrane and breach, pushing the vesicle contents (waste products or chemical transmitters) out of the cell.
Uses Of ATP
Energy from ATP is used to promote three major categories of cellular functions:
Transportof substances through multiple membranes in the cell
Synthesis of chemical compoundsthroughout the cell
Mechanical work-locomotion
Functions of Mitochondria
The most important function of the mitochondria is to produce energy and synthesis of ATP. The process is known as oxidative phosphorylation.
It is important to maintain proper concentration of calciumions within the various compartments of the cell.
In the liver cells have enzymes that detoxify ammonia.
Cytochrome C and second mitochondria-derived activator of caspases are involved in apoptosis.
Functions of Mitochondria
1.Synthesisof ATP -oxidative phosphorylation
2.Cell’s homeostasis of calcium
3.Regulation of the membrane potential
4.Regulation of cellular metabolism
5.Regulation of cellular proliferation
6.Detoxification of ammonia
7.Apoptosis-programmed cell death
Cilia
Tiny hair-like structures that project from the surface of the cell
Cylindrical structures that extend from the cell
Composed of microtubules which are enclosed by the cell membrane.
Numerous on the surface cells that line the respiratory tract, uterine tube.
Microvilli
Specialized extensions of the cell membrane that are supported by microfilaments.
Numerous folds (finger-like projections) increase surface area.
Abundant on the surface of cells in which absorption is an important function.
Flagella
Simple whip-like structure that propels sperm through its environment.