Biology Lesson 3: Cell Structures and Functions

Overview of Cell Structures and Functions

• Cells consist of the plasma membrane, cytoplasm, DNA, and ribosomes.
• Understanding the structure and function of these components is essential for biology studies.

Plasma Membrane

• Acts as a barrier regulating substance exchange between the cell and its environment.
• Composed of a phospholipid bilayer with polar heads outside and nonpolar tails inside.
• Embedded proteins perform various functions, including transport and signaling.

Cytoplasm

• A semifluid environment where cellular biochemical reactions occur.
• Composed of 80-85% water, with proteins (10-15%), lipids (2-4%), polysaccharides (1%), and nucleic acids (1%).

DNA (Deoxyribonucleic Acid)

• Genetic material in all cellular organisms and most viruses.
• Comprised of nucleotides with phosphate groups, deoxyribose sugars, and nitrogen bases (A, T, C, G).
• Carries instructions for protein synthesis and genetic replication.

Ribosomes

• Complexes made of ribosomal RNA and proteins functioning as sites for protein synthesis.
• Discovered in 1955 by George E. Palade; found in the cytoplasm and associated with the endoplasmic reticulum.

Prokaryotic Cell Structures

• Specifically focus on bacterial cell features, including organelles and their functions.

Flagella

• Motility structures with three parts: filament, hook, and basal body.
• Capable of 360-degree rotation; can be single, clustered, or distributed over the cell surface.

Fimbriae

• Hairlike bristles on the cell surface that assist in adhesion to other cells and surfaces.

Pili

• Rigid tubes made of pilin protein, unique to Gram-negative bacteria.
• Serve roles in bacterial conjugation (DNA transfer) and adhesion.

Glycocalyx

• Coating of sugar and/or protein molecules outside the cell wall.
• Two types: capsule (organized and tightly bound) and slime layer (loosely bound).
• Functions include adhesion, protection from white blood cell attacks, and receptor capabilities.

Cell Wall

• Composed of peptidoglycan, providing structural support and preventing lysis due to osmotic pressure changes.
• Differences between Gram-positive and Gram-negative bacteria:
  • Gram-positive: Thick peptidoglycan layer, retains crystal violet, stains purple.
  • Gram-negative: Thin peptidoglycan layer, loses crystal violet, stains red with safranin.

Cytoplasm (Prokaryotic)

• Dense, gelatinous solution with a high water content (70-80%).
• Serves as a solvent for materials involved in cellular functions.

Chromosome

• DNA found tightly coiled around proteins, essential for genetic information storage and transmission.
• Key element in cell replication and protein coding.

Overview of Cell Structures and Functions

• Cells consist of the plasma membrane, cytoplasm, DNA, and ribosomes.
• Understanding the structure and function of these components is essential for biology studies.

Plasma Membrane

• Acts as a barrier regulating substance exchange between the cell and its environment.
• Composed of a phospholipid bilayer with polar heads outside and nonpolar tails inside.
• Embedded proteins perform various functions, including transport and signaling.

Cytoplasm

• A semifluid environment where cellular biochemical reactions occur.
• Composed of 80-85% water, with proteins (10-15%), lipids (2-4%), polysaccharides (1%), and nucleic acids (1%).

DNA (Deoxyribonucleic Acid)

• Genetic material in all cellular organisms and most viruses.
• Comprised of nucleotides with phosphate groups, deoxyribose sugars, and nitrogen bases (A, T, C, G).
• Carries instructions for protein synthesis and genetic replication.

Ribosomes

• Complexes made of ribosomal RNA and proteins functioning as sites for protein synthesis.
• Discovered in 1955 by George E. Palade; found in the cytoplasm and associated with the endoplasmic reticulum.

Prokaryotic Cell Structures

• Specifically focus on bacterial cell features, including organelles and their functions.

Flagella

• Motility structures with three parts: filament, hook, and basal body.
• Capable of 360-degree rotation; can be single, clustered, or distributed over the cell surface.

Fimbriae

• Hairlike bristles on the cell surface that assist in adhesion to other cells and surfaces.

Pili

• Rigid tubes made of pilin protein, unique to Gram-negative bacteria.
• Serve roles in bacterial conjugation (DNA transfer) and adhesion.

Glycocalyx

• Coating of sugar and/or protein molecules outside the cell wall.
• Two types: capsule (organized and tightly bound) and slime layer (loosely bound).
• Functions include adhesion, protection from white blood cell attacks, and receptor capabilities.

Cell Wall

• Composed of peptidoglycan, providing structural support and preventing lysis due to osmotic pressure changes.
• Differences between Gram-positive and Gram-negative bacteria:
  • Gram-positive: Thick peptidoglycan layer, retains crystal violet, stains purple.
  • Gram-negative: Thin peptidoglycan layer, loses crystal violet, stains red with safranin.

Cytoplasm (Prokaryotic)

• Dense, gelatinous solution with a high water content (70-80%).
• Serves as a solvent for materials involved in cellular functions.

Chromosome

• DNA found tightly coiled around proteins, essential for genetic information storage and transmission.
• Key element in cell replication and protein coding.