Cell Structure and Function Quiz

### The Nucleus

• The largest feature in a cell
• Bound by a double membrane, the nuclear envelope, with the outer layer being continuous with the Endoplasmic Reticulum (ER).
• Pores in the membrane allow the passage of substances.
• 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.

Plasma (Cell) Membrane

• Partially permeable.
• Made up of two layers.
• Embedded with proteins and Na, phosphates, chlorides, amino acids, ATP, and storage material (oil droplets).

Mitochondrion (Mitochondria)

• The ‘powerhouse of the cell.’
• Contains an outer and inner membrane.
• Cristae (folded inner membrane) allow maximum surface area for chemical reactions to occur.
• Involved with cellular aerobic (O2) respiration, the process by which chemical energy is made available in the cell.
• Energy = ATP (Adenosine triphosphate) is formed from the catabolism of carbohydrates, fats, and proteins in the cell.
• Occur in varying numbers depending on the cell and its function, with the greatest number in cells that are physically and metabolically active (e.g., skeletal muscles).

Rough Endoplasmic Reticulum (RER)

• A series of interconnecting membranous canals which enclose flattened sacs called cisternae.
• Covered in ribosomes which make proteins.
• An extension of the outer nuclear membrane.
• Has a large surface area for chemical reactions.

Function of the Rough Endoplasmic Reticulum (RER)

• Produces proteins, especially enzymes.
• Pathway for the transport of materials through the cell.
• Collecting and storing synthesized material.
• Providing a structural skeleton to maintain cellular shape.

Smooth Endoplasmic Reticulum (SER)

• Similar features to RER but with no ribosomes.
• Found in large amounts in cells which secrete steroids, such as the adrenal cortex in the kidney.
• Concerned with the synthesis of lipids and steroid hormones.
• Contains enzymes for detoxifying chemicals, including drugs and pesticides.

Golgi Apparatus

• Composed of stacks of flattened membranous sacs called cisternae.
• Sacs are fluid-filled and pinch off smaller membranous sacs, called vesicles.
• Normally, only one Golgi apparatus in each animal cell.

Function of the Golgi Apparatus

• Packages and processes proteins received from the ER into vesicles prior to secretion.
• Vesicles then deliver them to their destinations (e.g., lysosomes or the cell membrane).
• This plays a key role in the secretory pathway.

Golgi Apparatus Continued…

• Producing secretory enzymes (e.g., digestive enzymes).
• Transporting and storing lipids.
• Receiving glyco-proteins such as mucin required.
• Secreting carbohydrates.
• Forming lysosomes.

Lysosome and its Function

• A membrane-bound cell organelle that contains digestive enzymes.
• If a cell is damaged beyond repair, lysosomes can help it to self-destruct by apoptosis (programmed cell death).
• They destroy invading viruses and bacteria.
• They break down excess or worn-out cell parts.
• Help to break down food particles when cells engulf them.

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

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

### Microfilaments

• Fine, thread-like protein fibres, 3-6 nm in diameter.
• Composed predominantly of a contractile protein called actin, which is the most abundant cellular protein.
• Can also 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.
• Involved in intracellular transport (e.g., diffusion, osmosis, active transport, phagocytosis, pinocytosis).

Diffusion

• The process by which a substance moves from a region of high concentration to a region of low concentration.
• The rate is variable and depends on the concentration gradient, distance, the size of the area, structure in the path, and the size of the molecule.

Osmosis

• The passage of water down its concentration gradient towards equilibrium across a semi-permanent membrane.
• Occurs when solute molecules are too large to pass through the pores in the membrane by diffusion.

Active Transport

• The transport of substances up their concentration gradient (i.e., from a lower to a higher concentration).
• Chemical energy (ATP) drives protein molecules in the membrane that transport substances across the membrane in either direction.
• E.g., the sodium-potassium pump maintains homeostasis of electrolytes sodium and potassium.

### Phagocytosis

• The process by which the cell can obtain particles which are too large to be absorbed by diffusion or active transport.

### Pinocytosis

• ‘Cell drinking’ is very similar to phagocytosis except vesicles are produced called 'pinocytotic vesicles.'
• Used for the intake of liquids rather than solids.
• Both pinocytosis and phagocytosis are methods by which materials are taken into the cell in bulk (endocytosis).
• The reverse process – materials are removed from the cell (e.g., waste products) – exocytosis.

Abnormal Cell Growth

• Hyperplasia: A term referring to the proliferation of cells within an organ or tissue beyond that which is ordinarily seen (i.e., constant cell division).