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.