Cytology hard

Nucleus

• Stores genetic material (DNA)
• Directs all metabolic activities of the cell, including growth, metabolism, protein synthesis, and reproduction (cell division)
• Involved in cell division
• Instructs the synthesis of proteins/ribosomes & RNA
• Fundamental to cell survival

Plasma Membrane

• Controls the passage of substances in and out of the cell, regulating the intracellular environment
• Partially permeable
• Composed of two layers of lipids (mostly phospholipids)
• Phospholipids are hydrophilic ("water-loving") at their phosphate ends – facing outwards, and hydrophobic ("water-fearing") along their lipid tail regions – orientated inwards
• Embedded with proteins and carbohydrate molecules, which influence the transfer of substances that pass through the membrane
• Proteins passing all the way through the membrane allow for passage of electrolytes

Lysosomes

• A secretory vesicle formed by the Golgi apparatus
• Contain enzymes responsible for degrading proteins and membranes in the cell
• Aids degradation of materials ingested by the cell (due to hydrolytic (digestive) enzymes)
• Enzymes are kept apart from the cell to prevent them from destroying the cell's contents
• Kept inactive by an alkaline environment within the lysosome
• Abundant in cells with phagocytic activity, e.g. leukocytes

Lysosomes continued: Functions

• Autophagy: A process involving the degradation of a cell's own components through the lysosomal machinery
• Self Destruction: They release enzymes outside the cell (exocytosis) in order to break down other cells
• Autolysis: The destruction of a cell through the action of its own enzymes

Centrosome

• Directs the organization of microtubules within the cell
• Comprises a pair of centrioles (small clusters of microtubules)
• Plays an important part during cell division

Centrosome Function: Cell Division

• 2 centrioles, cylindrical structures, orientated at right angles to each other
• Act as organizers of the nuclear spindle during cell division

Microfilaments

• Composed predominantly of a contractile protein called actin, which is the most abundant cellular protein
• Fine, thread-like protein fibers, 3-6nm in diameter.
• Can carry out cellular movements, including gliding, contraction, and cytokinesis (the division of cytoplasm following division of a nucleus)
• Association with the protein myosin is responsible for muscle contraction

Microtubules

• Cylindrical tubes, 20-25nm in diameter, providing mechanical support and structure to the cell
• Involved in intracellular transport, e.g. the movement of chromosomes during cell division
• Important in the formation of flagella and cilia, which help move fluids and cells

Chromosomes

• Diploid = Complete set of chromosomes
• Gametes = Haploid (single set of chromosomes)

Meiosis

• A form of cell division which produces gametes
• Results in two genetically different daughter cells
• The homologous pairs swap some DNA
• Each daughter cell has 23 chromosomes only - haploid

Meiosis I

• The stages are similar to mitosis
• Homologous chromosomes pair up
• Homologous pairs divide and 2 daughter cells are produced

Meiosis II

• Genetic material in daughter cells is halved by a second division
• One chromosome from the original pair form a gamete
• 4 daughter haploid cells are produced

Cellular Transport

• The passage across cell plasma membranes is semi-permeable.

Transport of Substances Across Cell Membranes

• Passive transport: Diffusion and osmosis (no energy required)
• Active transport: Uses ATP (energy) to move substances against their concentration gradient.
• Bulk transport: Pinocytosis & Phagocytosis

Types of Cell Transport

• Diffusion: The process by which a substance moves from a region of high concentration to a region of low concentration
• Osmosis: The passage of water down its concentration gradient towards equilibrium across a semi-permeable membrane
• Active transport: Movement of a substance against its concentration gradient; requires ATP
• Phagocytosis: Cell engulfs large particles (e.g., bacteria)
• Pinocytosis: Cell engulfs fluids and dissolved substances

Lysosome Function: Apoptosis

• If a cell is damaged beyond repair, lysosomes help it to self-destruct by apoptosis (programmed cell death)
• Destroy invading viruses and bacteria
• Break down excess or worn-out cell parts

Test your knowledge on essential cell components including the nucleus, plasma membrane, and lysosomes. This quiz covers their structures, functions, and importance to cell survival and metabolism. Prepare to explore how these organelles contribute to the overall functioning of cells.