Cells

List the general functions of cells in the human body

Covering, lining, storage, movement, connection, defence, communication, reproduction

Describe the contents of a prototypical cell

A generalised cell that does not actually exist in the body. Combines features from a variety of different cells for teaching purposes.

Plasma membrane structure

A phospholipid bi-layer creating an extremely thin outer border of the cell. Lipids form most of the membranes structure while proteins are responsible for its function.

Lipids

Insoluble material e.g. fats, oils and steroids. majority of lipids in plasma membrane are phospholipids but also contains cholesterol and glycolipids.

Proteins

Large molecules (macromolecules) made up of amino acid chains. 2 types of membrane proteins: integral and peripheral.

Structure of phospholipids

Made up of a polar (charged) hydrophilic head and a non-polar hydrophobic tail. When exposed to an aqueous environment they for a phospholipid bi-layer.

Function of cholesterol

About 20% of lipids in the cell membrane, strengthens and stabilises membrane against extreme temperatures.

Function of glycolipids

About 5-10% of lipids in the cell membrane, have carbohydrate molecules attached facing out and forming the glycocaylx.

Function of plasma membrane

Selective physical and chemical barrier that decides what enters and exits the cell. Regulates the passage of gases, nutrients, and wastes between the internal and external environments of the cell.

3 parts of the cytoplasm

Cytosol, inclusions, organelles

Cytosol definition

Viscous fluid, containing many different dissolved substances e.g. ions, nutrients, proteins, carbohydrates, amino acids

Inclusions definition

Large storage aggregates of complex molecules found in the cytosol e.g. melanin and glycogen

Organelles definition

Many types each performing a different function. The type and number of organelles within a cell correlates with its function. They an be classified as membrane or non-membrane bound.

Endoplasmic Reticulum structure

A network of intracellular membrane-bound tunnels. Can be classified as rough or smooth. Walls of Rough ER have ribosomes attached to the outside.

Rough ER function

Functions to synthesise, transport or store proteins for: secretion by the cell, incorporation into the plasma membrane, creation of lysosomes.

Smooth ER function

Synthesis, transport and storage of lipids including steroid hormones. Metabolism of carbohydrates and detoxification of drugs, alcohol, and poisons.

Golgi apparatus structure

Stacked cisternae with lateral edges which bulge, pinch off, and give rise to small transport and secretory vesicles.

Vesicle definition

Membrane bound structures containing proteins and other substances.

Function of Golgi apparatus

To receive proteins and lipids from the Rough ER for modification, sorting, and packaging

Lysomes definition

Vesicles generated but the Golgi apparatus. Contains enzymes used to digest and remove waste products and damaged organelles within the cell (autophagy). When a cell is dying it releases lysosomal enzymes that digest the cell (autolysis)

Peroxisomes definition

Vesicles smaller than lysosomes. Use O2 and catalase to detoxify harmful molecules taken into the cell. E.g. Turns hydrogen peroxide into water and also breaks down fatty acid molecules.

Mitochondria Structure

Bean shaped organelles with a double membrane. Inner membrane folded into shelf-like shapes with an internal matrix.

Mitochondria Function

To produce Adenosine Triphosphate (ATP). Cells that require more energy will have more mitochondria.

Ribosomes

Responsible for protein synthesis, found free floating in the cytosol and fixed to the outside of the rough ER.

Cytoskeleton

Provides structural component of the cell, stabilises cell junctions and helps move organelles and materials through the cell.

Cilia

Grouped on cells that move objects across their surface (e.g. trachea)

Flagella

Longer, usually singular to propel a cell (e.g. sperm)

Micro Villi

Extensions of cells, not capable of motion, increase surface area to increase the absorption of food. Found in the small intestine.

Nucleus

Control centre for cellular activity, contains DNA. When not dividing DNA is unwound into chromatin, during cell division it is coiled tightly into chromosomes.

Nuclear Envelope

Double membrane structure that controls entry and exit of molecules between nucleus and cytoplasm. Outer membrane continuous with the endoplasmic reticulum. Nuclear pores are selectively permeable channels which allow this.