Cell Structure

Cells…. A cell is the smallest unit that is capable of performing life functions. The size & shape of a cell relates to its function (job it does).

Prokaryotic Cells Cells without membrane-bound structures. Eg: bacteria. Can you name some types of bacteria?

Eukaryotic Cells Cells with membrane-bound structures. Eg: animals, plants, fungi and protists.

Cell wall Protects the cell. Gives the cell its shape. Made of cellulose. A cell wall is found in plants, algae, fungi, and most bacteria.

Cell/Plasma Membrane Outer covering of the cell. Protective layer around ALL cells. For cells with cell walls, the cell membrane is inside the cell wall. Allows food, oxygen, and water into the cell and waste products out of the cell.

Cytoplasm Gelatin-like fluid inside cell membrane. Constantly flowing around the cell. Consists mainly of water with dissolved substances.

Cytoskeleton Scaffolding-like structure in cytoplasm. Helps the cell maintain or change its shape. Made of protein.

Nucleus Directs all cell activities. Contains instructions for everything the cell does. These instructions are found on a hereditary material called DNA. The largest organelle in the cell.

Nucleolus Found within the nucleus. Responsible for the production of ribosomes.

Chloroplasts Green organelles that make food. Found only in plant cells.

Chlorophyll Found within the chloroplast. A green pigment that gives leaves & stems their colour. Captures sunlight energy that is used to produce food called glucose. Glucose is a type of sugar.

Mitochondria Organelles are the powerhouse of a cell because they release energy from food . This energy is released by breaking down food into carbon dioxide (CO2). Some muscle cells have 20,000 mitochondria. Why would these cells need so many mitochondria?

Ribosomes Make proteins. Float freely or attached to the endoplasmic reticulum (ER). Ribosomes are made in the nucleolus.

Endoplasmic reticulum A series of folded membranes that move proteins around in a cell. Smooth ER – ribosomes NOT attached to ER. Rough ER – ribosomes attached to ER.

Golgi apparatus Stacked and flattened membranes. Function is to sort, package and ship proteins that are produced in the endoplasmic reticulum (ER).

Vacuoles Temporary storage spaces. Store food, water, waste. Vacuole

Lysosomes The word "lysosome" is Latin for “kill body”. The purpose of the lysosome is to digest things such as food molecules, cell wastes and worn out cell parts.

Packaging and transport of biomacromolecules within a cell

The Nucleus: Genetic Library of the Cell The nucleus contains most of the cell’s DNA, and the ribosomes which use information from the DNA to make proteins. The nuclear envelope encloses the nucleus, separating its contents from the cytoplasm. The nuclear envelope is lined with nuclear pores which regulate the entry and exit of large macromolecules and particles. The DNA within the nucleus is arranged into discrete units called chromosomes. Each chromosome is made up of chromatin, a complex of proteins and DNA.

The Nucleolus The nucleolus is found within the nondividing nucleus. Within the nucleolus, a special type of RNA called ribosomal RNA (rRNA) is synthesised from instructions from the DNA. Proteins are imported from the cytoplasm and are assembles with rRNA into large and small subunits in the nucleolus. These subunits then exit the nucleus via the nuclear pores into the cytoplasm, where they are involved in the production of proteins.

Ribosomes: Factories in the Cell Ribosomes are particles made of ribosomal RNA and protein, and are the organelles that carry out protein synthesis. Ribosomes produce proteins in two prominent locations around the cell. Free ribosomes suspended in the cytoplasm: most of the proteins made here function within the cytosol. Bound ribosomes that are attached to the outside of the endoplasmic reticulum: the proteins made here are usually destined for insertion into membranes, for packaging within certain organelles such as lysosomes, or for export from the cell (secretion).

The Endomembrane System The endomembrane system regulates protein traffic and performs metabolic functions. The endomembrane system includes: The nuclear envelope Endoplasmic reticulum Golgi apparatus Lysosomes Vacuoles Plasma membrane The endomembrane system carries out a variety of tasks including: Synthesis of proteins and their transport within or outside of the cell Metabolism and movement of lipids Detoxification of poisons

The Endoplasmic Reticulum (ER) The endoplasmic reticulum is continuous with the nuclear envelope. The ER is involved in the transport of proteins and lipids within the cell. There are two distinct, though connected, regions of ER that differ in structure and function The Smooth ER (no ribosomes attached to surface). Important in the synthesis of lipids, including oils, phospholipids, and steroids. Contains enzymes which help to detoxify drugs and poisons, especially in liver cells. Stores calcium ions which are essential for the functioning of muscles. Rough ER (ribosomes are attached to the surface). Synthesises secretory proteins Synthesises phospholipids which are either attached to the ER membrane, or transported in the form of stransport vesicles to other compartments of the endomembrane system

The Golgi Apparatus: Shipping and Receiving Centre After leaving the ER, many transport vesicles travel to the Golgi apparatus In the Golgi apparatus, products of the ER are modified and stored and then sent to other destinations. There are vesicles concentrated in the vicinity of the Golgi apparatus which are involved in the transfer of material between the parts of the Golgi and other structures. The Golgi modifies products from the ER to produce a large variety of carbohydrates. The Golgi also manufactures some macromolecules on its own, including many non-cellulose polysaccharides.

Lysosomes: Digestive Compartments Lysosomes are membrane-bound sacs within the cytoplasm of animal cells that contains enzymes that are responsible for: The digestion of material in food vacuoles. The destruction of foreign bodies entering the cell (eg: bacteria). The breakdown of cell structures when the cell dies. A similar structure to the lysosome is present in plant cells

Vacuoles: Maintenance Compartments A vacuole is a fluid filled sac found in the cytoplasm of cells. Vacuoles are small and temporary in animal cells. Plant cells have one large permanent vacuole which is filled with cell sap Food vacuoles are produced via the process of phagocytosis.

Summary