CELLS

1
CELLS

• CHAPTER 3

2
Introduction

• Cells are the basic structural and functional
  unit of all living organisms.
• Study of cells cytology
• Cell theory
• All organisms made of cells
• Cell is the basic unit of life
• New cells arise from preexisting cells

3
Parts of a cell

• The principal parts of a cell are
• 1. Plasma membrane the outer boundary
• 2. Cytosol the fluid material in the interior.
  Contains mostly water, ions, sugar,amino acids,
  lipids, ATP, wastes. Site for chemical
  reactions.
• 3. Organelles structures found within that
  perform a specific function. Some organelles are
  membranous and others are non membranous.
• 4. Nucleus the largest organelle that controls
  all cellular functions.

4
Cellular Organelles

• Cytoskeleton a network of protein filaments.
  Microfilaments, intermediate filaments,
  microtubules. Provides structural framework and
  responsible for cell movements.
• Centrosome consists of centrioles. Responsible
  for cell division process mitosis and meiosis.
• Cilia and flagella hair-like projections. Move
  fluid along cell surface or entire cell.
• Ribosomes made of RNA and protein. Small and
  large subunits. Sites for protein synthesis.

5
Cellular Organelles

• Endoplasmic reticulum (ER) network of membranes
  that form sacs or tubules called cisterns. Rough
  ER covered by ribosomes and function is protein
  synthesis. Also forms glycoproteins. Smooth ER
  lacks ribosomes. Synthesizes steroids, fats
  phospholipids. Inactivates or detoxifies harmful
  drugs.
• Golgi Complex contains flattened sacs. It
  receives synthesized products from ER and then
  sorts, modifies, packages and transports or
  secretes them to various destinations.

6
Cellular Organelles

• Lysosomes membrane bound organelles that contain
  digestive enzymes. Function in digestion of
  worn-out organelles, digestion of foreign
  invaders, and extra cellular digestion.
• Peroxisomes similar to lysosomes but smaller.
  Contain catalase that degrades hydrogen peroxide.
• Mitochondria double-membrane structures. Inner
  membrane has folds called cristae and a
  fluid-filled cavity called the matrix. It is
  the powerhouse of the cell as most of the ATP is
  generated here by cellular respiration.

7
Nucleus

• Largest organelle of the cell.
• Consists of a double nuclear envelope.
• Nuclear pores allow for the exchange of material
  between the nucleus and cytoplasm.
• Fluid of nucleus nucleoplasm.
• Chromatin genetic material. Made of DNA and
  protein. Chromosomes.
• Nucleolus pre-assembly site for ribosomes.
• Genes (found on chromosomes) control cellular
  structure and most cellular functions.

8
Plasma Membrane

• Surrounds and contains of the cytoplasm of the
  cell.
• It contains a 5050 mix of protein and lipids.
• The fluid-mosaic model the membrane is a mosaic
  of proteins floating like icebergs in a sea of
  lipid bilayer.
• The major lipid is phospholipid (bilayer), also
  present is cholesterol and glycolipids.
• Proteins integral or peripheral. Also
  glycoproteins.

9
Plasma membrane

• Membrane proteins serve various functions.
  Channels or transporters help specific solutes
  to enter. Receptors recognize specific
  molecules. Other proteins function as enzymes or
  cell-identity markers.
• Membrane is selectively permeable. The lipid
  bilayer permits water, gases, nonpolar
  substances. Proteins allow for ions and charged
  molecules to pass through.
• Membrane is a fluid structure. Fluidity
  increased by unsaturated fatty acids. The
  bilayer can self-seal when torn or punctured.

10
Transport processes

• Passive and Active mechanisms. In passive
  transport molecules move down the concentration
  gradient. In active transport molecules move
  uphill against concentration gradient.
• In vesicular transport, tiny vesicles either
  detach from or merge with the plasma membrane to
  move materials across the membrane.

11
Passive transport

• In net diffusion molecules move from a high
  concentration area to a low concentration area
  until an equilibrium is reached. The rate of
  diffusion depends on steepness of concentration
  gradient, temperature, size or mass of diffusing
  substance. Eg. Oxygen, carbon dioxide, alcohols,
  steroids, fat soluble vitamins.
• Ion channels allow diffusion across the membrane
  of small inorganic ions of sodium, potassium,
  calcium, chloride.
• In facilitated diffusion, a solute such as
  glucose binds to a specific transporter protein
  and is carried inside or outside the cell. Eg.
  Glucose, amino acids.

12
Osmosis

• Net movement of water across a selectively
  permeable membrane from an area of high water
  concentration to an area of low water
  concentration.
• Isotonic solution
• Hypotonic solution
• Hypertonic solution

13
Active Transport

• Movement of molecules from a low concentration
  area to a high concentration area with the
  expenditure of ATP energy. Also requires a
  transport protein. Eg. Sodium, potassium,
  hydrogen, chloride, iodide, calcium ions.
• The most prevalent primary active pump is the
  Na/K pump.
• Secondary active transport symporters and
  antiporters.

14
Vesicular transport

• Endocytosis phagocytosis and pinocytosis.
  Phagocytosis is the ingestion of solid particles.
  Pinocytosis is the ingestion of extracellular
  fluid.
• Receptor-mediated endocytosis is the selective
  uptake of large particles and molecules called
  ligands.
• Exocytosis involves movement of secretory or
  waste products out of a cell by fusion of
  vesicles with the plasma membrane.

15
Cell Division

• Cell division is the process by which cells
  reproduce themselves. It consists of nuclear
  division(mitosis) and cytoplasmic division
  (cytokinesis).
• Cell division that results in an increase in the
  number of cells involves mitosis.
• Cell division that involves production of sperm
  or ova involves meiosis.

16
Cell cycle

• It is divided into interphase, mitosis and
  cytokinesis.
• Interphase is further divided into G1, S and G2
  phases.
• G1 phase cell duplicates its organelles and
  cytosolic contents.
• S phase during this phase DNA replication
  occurs.
• G2 phase enzymes and other proteins are
  syntyhesized.

17
Mitosis

• Mitosis is divided into prophase, metaphase,
  anaphase and telophase.
• Prophase nuclear envelope disintegrates,
  nucleolus disappears, centrioles start moving to
  opposite poles, spindle apparatus is formed,
  chromosomes are visible.
• Metaphase chromosomes are aligned along the
  equator of the cell.
• Anaphase the chromatids are pulled apart to
  opposite poles.

18
Mitosis and Cytokinesis

• Telophase reappearance of nuclear envelope,
  chromatin, nucleolus. Cleavage furrow.
• Cytokinesis cytoplasmic division to form two
  identical daughter cells.
• Certain genes regulate both cell division and
  apoptosis (programmed cell death).

19
Cancer

• Uncontrolled cell division.
• Tumor or neoplasm excess tissue in a part of the
  body.
• Cancerous tumor is malignant tumor.
• Metastasis ability to spread to other parts.
• Benign tumor noncancerous tumor.