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Cell

Components & Functions

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Cell

  • Cell is the basic, living, structural & functional unit of all living organisms.
  • Cytology – study of cell
  • All cells come from preexisting cells through cell division.
  • Microscopic - Many cannot be seen with the naked eye.
  • The size & shape is variable.

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Types of cell

  • 1. Prokaryotic
  • 2. Eukaryotic

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Prokaryotic cell

  • Do not have structures surrounded by membranes

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  • Few internal structures
  • One-celled organisms, Bacteria
  • No membrane bound nucleus, but instead Nucleoid = region of DNA concentration

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Eukaryotic cell

  • Contain organelles surrounded by membranes
  • Most living organisms - fungi, protists, plant, and animal cells.
  • Possess many organelles.
  • Infinite number of shapes and purposes.
  • Human body has at least 85 different cell types.

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Typical plant cell

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Typical animal cell

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Cell

Components

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  • Cell consists of
    • 1. Cell membrane
    • 2. Protoplasm
        • a. Cytoplasm with matrix & organelles
        • b. Nucleus

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Cell membrane/plasma membrane

  • Outermost membrane of cell
  • Acts as gate keeper - that controls movement in and out of the cell
  • Double layer of phospholipids & proteins.
  • Thin layer of 5 – 10 nm.
  • The phospholipid is bilayer with head & tail part.
      • Head – hydrophilic
      • Tail - hydrophobic

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Membrane proteins

1. Channels or transporters

    • Move molecules in one direction

2. Receptors

    • Recognize certain chemicals

3. Glycoproteins

    • Identify cell type

4. Enzymes

    • Catalyze production of substances

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Functions of cell membrane

  • Provide shape to the cell
  • Gives support & protection to the inner organelles.
  • Membrane proteins acts as specific receptors for chemicals
  • Glycoproteins gives immunological identity
  • Transportation of soluble substances, liquids, ions, food materials, drugs etc.
  • Membrane proteins acts as enzymes

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Nucleus

  • Largest and most identifiable part of the cell
  • Brain or Control center of cell.
  • Round or oval structure
  • Typically found in the middle of the cell
  • Appears darker than surrounding material.
  • Surrounded by bi-layered nuclear membrane made of phospholipids.
  • Small openings allow material to enter and leave nucleus

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  • Nucleus contains Chromatin & Nucleolus.
  • Chromatin contain genetic material (in the form of DNA) & proteins. Chromatin condenses to form chromosomes when the cell divides.
  • Nucleolus is tiny, spherical dark staining body consisting of 95% proteins & 5% RNA.
  • One or more nucleolus present.
  • Forms ribosomes & directs synthesis of RNA
  • Ribosomes then migrate to the cytoplasm through nuclear pores

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Functions of nucleus

  • Controls cellular activity.
  • Cell division
  • Synthesis of proteins & enzymes
  • Site for synthesis of ribosomes (Nucleolus)
  • Inheritance of genetic characteristics.

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Cytoplasm

  • Is granular, homogenous, viscous gel like structure present within the cell.
  • components of cytoplasm
    • fluid = cytosol/matrix
    • organelles (not nucleus)
  • Cytosol – watery fluid (75-90% water), where organelles are suspended.
  • It contains storage substances like proteins, carbohydrates, fats, minerals, vitamins, waste materials, tubules & filaments etc.

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Cell organelles

  • Metabolic machinery of the cell
  • Includes different structures with characteristic structure, role & functions.
  • They are classified into-
      • Non-membranous: Cytoskeleton, Centrioles, Cilia.
      • Membranous: Mitochondria, Endoplasmic reticulum, Golgi bodies, Ribosomes, Lysosomes, Peroxisomes etc

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Mitochondria

  • “Powerhouses” of the cell - Produces energy through chemical reactions by breaking down fats & carbohydrates
  • Provides ATP for cellular energy.
  • Double membranous,Change shape continuously.
  • Outer membrane – smooth, Inner membrane – folded called as cristae.
  • Inner membrane enclose the fluid called as matrix & enzymes are found in cristae & matrix.

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Mitochondria

  • Each cell contains around 100 mitochondria, but active cells like Muscles, Liver, Kidney tubules contain around 1000.
  • Have their own DNA.
  • Can self-replicate

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Endoplasmic Reticulum

  • Network of fluid filled interconnected tubules in cytoplasm.
  • Extended from nuclear membrane to cell membrane.
  • 2 Types-
      • 1. Smooth ER
      • 2. Rough ER

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Rough ER (granular)

  • Presence of ribosomes on surface.
  • Site for synthesis of building materials of cell membrane – proteins.
  • Temporary storage of proteins, where sugar is attached to form glycoproteins.

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Smooth ER (Agranular)

  • No ribosomes.
  • Site for cholesterol synthesis & breakdown, Fat metabolism, steroid synthesis.
  • Enzymes may also be present – inactivation of chemicals like alcohol, pesticides, carcinogens etc.
  • In muscle cell – Sarcoplasmic reticulum – stores calcium ions.

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Ribosomes

  • Tiny granules made of protein and RNA
  • Each cell contains thousands
  • Sites of protein synthesis
  • Found at two locations

1. Free in the cytoplasm

2. Attached to rough endoplasmic reticulum.

  • Free ribosomes are concerned with synthesizing of proteins for use inside the cell.
  • Bounded ribosomes – synthesis of proteins for plasma membrane or for export.

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Golgi bodies

  • Golgi apparatus, located near to nucleus.
  • Similar to ER - Look like a thick elastic band that has been folded several times.

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  • Consists of thick flattened sacs called as cisterns, which are stalked upon each other like pile of plates with expanded bulges at the edges.
  • Small golgi vesicles are associated with cisterns.

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      • Collect, modifies, package, and distribute molecules synthesized at one location in the cell and utilized at another location.
      • Produces 3 types of vesicles
          • Secretory vesicles (exports proteins outside)
          • Membranous vesicles (replaces damaged PM)
          • Storage vesicles (Lysosomes & Peroxisomes)

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Lysosomes

  • Small round membrane bound vesicles formed in Golgi complex.
  • Contains 40 different enzymes including hydrolytic (digestive) enzymes.
  • Responsible for digestion of carbohydrates, amino acids, DNA, RNA & fats & send the products to cytosol.
  • Responsible for digestion of bacteria & other foreign substances that enter the cell.
  • Helps to digest the cell’s own organelles (old) & cellular debris – suicidal bags

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Cytoplasm

Phagocytosis

Food

vesicle

Golgi

apparatus

Lysosomes

Plasma

membrane

Digestion of

phagocytized

food particles

or cells

Endoplasmic

reticulum

Transport

vesicle

Old or damaged

organelle

Breakdown

of old

organelle

Extracellular

fluid

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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Peroxisomes

  • Small spherical membrane bound vesicles containing oxidase enzymes.
  • The oxidase enzyme molecular oxygen to oxidise various organic substances. Hydrogen peroxide is produced as byproduct, which is utilized by enzyme catalase to oxidise or detoxify various harmful substances like HCOOH, HCHO, alcohol, phenol etc.
  • Play important role in Liver & Kidney.

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Cytoskeleton

    • Network of protein structures that extend throughout the cytoplasm.
    • Provides the cell with an internal framework.
    • 3 types –Microfilaments, Microtubules & Intermediate filament.

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Microfilaments

  • Rod like structures with varying length
  • Made up of protein Actin.
  • Actin provides
        • Contraction & Relaxation of muscular cell.
        • Support & shape to non-muscle cell.
        • Movement of cell
        • Movement of substances within the cell

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Microtubules

  • Long, cylindrical tubules made up of protein Tubulin.
  • Facilitates cell movement.
  • provides support & movement of chromosomes during cell division.

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Intermediate filaments

  • Sized between MF & MT.
  • Strong & tough
  • Provide reinforcement in the cell.
  • Hold organelles
  • Provide shape to the cell.

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Centrosome

  • Made up of pair of tiny cylindrical structures called as centrioles, which can be seen only when cell is dividing.
  • Near to the nucleus.
  • Rod shaped bodies, made up of microtubules.
  • Directs formation of mitotic spindle during cell division.

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Cilia & Flagella

  • Cellular projections not found in all cells.
  • Made up of microtubules (9 + 2 arrangement) & covered by membrane.
  • Cilia are projected,

Numerous hair like structure,

Responsible for extracellular

Substance movement.

Ex. Movement of Ovum in FT,

Movement of mucus in RT.

Flagella are few in number, long & responsible for cellular movement. (Ex- Tail of spermatozoa)

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Questions

  • Draw a neat labelled diagram of cell
  • Why mitochondria is called as power house of the cell.
  • Why Lysosomes are called as Suicidal bags of the cell.
  • Write the functions of Plasma membrane & Nucleus.
  • Write a note on Golgi apparatus.
  • What is difference between rough & smooth ER