ET

Cell+Structure+and+Function

Cell Structure and Function

Microscopes

  • Microscopes are tools developed to visualize cells and cellular structures clearly.

  • The Light Microscope (LM) is the most frequently used microscope in laboratories:

    • Light passes through a specimen then through glass lenses.

    • Specimens can be magnified up to 1,000 times their actual size.

Types of Microscopes

  • Light Microscope:

    • Can display living cells.

    • Suitable for observing cell shapes and movement.

  • Electron Microscope (EM):

    • Resolves biological structures as small as 2 nanometers.

    • Magnifies up to 100,000 times; uses a beam of electrons.

  • Magnification is the increase in an object’s image size versus its actual size.

  • Resolution indicates image clarity, showcasing nearby objects as separate.

Cell Size and Surface Area

  • Most cells are microscopic; their small size ensures a higher surface-to-volume ratio, facilitating:

    • Efficient nutrient and oxygen absorption.

Cell Theory

  • Formulated from 1800s studies of cells:

    • All living things are composed of cells.

    • All cells arise from pre-existing cells.

Internal Structures of a Cell

Organelles

Nucleus

  • Contains most of the cell's DNA and controls cell activities by directing protein synthesis via messenger RNA (mRNA).

  • Organizes DNA into chromosomes.

  • In non-dividing cells, DNA is found as chromatin, appearing as diffuse mass.

Endoplasmic Reticulum (ER)

  • Rough ER:

    • Synthesizes membrane and secretory proteins.

  • Smooth ER:

    • Involved in lipid synthesis, metabolism of carbohydrates, drug detoxification, and calcium ion storage.

Golgi Apparatus

  • Functions as a processing and shipping station.

  • Modifies, sorts, and packages cellular products for transport to various destinations.

Lysosomes

  • Membrane-enclosed sacs containing digestive enzymes produced by Rough ER.

  • Functions:

    • Digests food, recycles damaged organelles, destroys engulfed bacteria.

Chloroplasts

  • Photosynthesis: converts light energy to chemical energy in the form of sugars.

  • Major organelles in photosynthetic organisms like plants and algae.

Mitochondria

  • Site of cellular respiration, converting food chemical energy into ATP.

  • Contains DNA and ribosomes similar to prokaryotic cells, supporting the endosymbiont theory.

Cytoskeleton

  • Composed of three types of fibers:

    • Microfilaments (Actin Filaments):

      • Support cell shape and motility.

    • Intermediate Filaments:

      • Reinforce cell shape, anchor organelles.

    • Microtubules:

      • Shape the cell, serve as tracks for motor proteins.

Vacuoles

  • Large vesicles with varied functions:

    • In plants: storage, digestion, and maintenance of turgor pressure.

    • In protists: contractile vacuoles eliminate excess water.

Cell Junctions

  • Various types facilitate cell communication:

    • Tight Junctions: prevent leakage.

    • Anchoring Junctions: attach cells to each other.

    • Communicating Junctions: allow small molecules to pass between cells.