Lecture Notes-15 Biology 1004

North Arkansas College

Topic: Cell Structure and Function

Ribosomes

1. Spherical bodies
2. Located along the endoplasmic reticulum (ER).
3. Synthesize protein and composed of 80S (ribosomal subunits), each of which is made of two subunits (60S and 40S). S = Svedurg units: a measure of ribosomal size based on rates of sedimentation.
4. Prokaryotic ribosomes are 70S; made of 50S and 30S ribosomal subunits.

1. Function in protein synthesis.
2. They are made up of 60% RNA and 40% protein.
3. 80S - the ribosomal subunits are 60S and 40S.
4. Prokaryotes have 70S ribosomes with 50S and 30S ribosomal subunits.
5. Will often find many ribosomes synthesizing the same protein.

1. A series of complex internal membranes in eucaryotes termed endomembrane system.
2. The endomembrane compartmentalizes cell components, enzymes and specific chemical reactions.

1. Endoplasmic Reticulum

1. Flattened chemicals extending from the nucleus to the outer membrane.
2. There are two types of endoplasmic reticulum.

Rough ER - studded with ribosomes on the side facing the membrane. The site for protein synthesis.

Smooth ER - faces interior side, and runs parallel to the rough ER. The smooth ER does not have ribosomes and, therefore, has a smooth surface.

1. Synthesis of lipids (find in adrenal glands, testes, etc.) and steroids.
2. Detoxify drugs (including alcohol) - liver, etc. When alcohol is consumed regularly, the amount of smooth ER increases allowing more alcohol to be consumed (hence the tolerance often seen in alcoholics).
3. Transport vesicle (membrane bound bag) - moves large molecules into the cell.
4. Storage site of calcium ions. Muscle cells release calcium for muscle contractions.

1. Composed of 3-20 slightly curved sacules (look like stacks of pancakes). Large warehouse in cell.
2. In animal cells, one side of the Golgi apparatus faces membrane, and the other side faces the interior of the cell.
3. Contains proteins such as enzymes, which modify the proteins. Sugars can be added to proteins to form glycoproteins.
4. Packages cellular materials into vesicles (membrane bound sacs) and secretes these cellular materials out through the membrane to the outside of the cell. Golgi apparatus may also move substances from one cellular location to another.

1. Not found in plants.
2. Membrane bound vesicles produced by the Golgi apparatus.
3. Contain hydrolytic digestive enzymes that degrade waste materials in the cell.
4. Lysosomal enzymes participate/responsible for removal of tail during maturing of frogs.
5. These enzymes also digest tissue from between the toes and fingers, etc. from developing fetus during embryonic development.
6. Phagocytes (WBC’s that engulf and destroy invading foreign particles) combine with lysosomes in the cell to produce phagolysosomes. The lysosomes provide the enzymes, acids, peroxides, etc. to digest the foreign particles.
7. In some cases, the lysosomes either accumulate, or cells are deficient in lysosomes. This can create various diseases. Lysosomal deficiencies are responsible for Tay-Sachs à mental retardation, blindness. In Rheumatoid Arthritis, WBC’s synovial tissue (tissue lining spaces) leaks digestive enzymes into joints.
8. Lysosomes are involved in auto digestion.

1. Large sac surrounded by membranes.
2. Storage for proteins, sugars, water, salt, pigment and toxic substances.
3. In plant cells, observe 1 large central vacuole.
4. In Protist, such as Paramecium, observe contractile vacuoles.

1. Powerhouse of cell where energy is produced as ATP during process of respiration.
2. Mitochondria are double membrane structures with cytosol.
3. The membrane of mitochondria contains stalk shaped structured called cristae that contain respiratory enzymes for ATP production.
4. Anaerobes (no 0₂) have no mitochondria.
5. Mitochondria have their own DNA (very stable over time), and their own ribosomes (70S rather than 80S). These may be prokaryotes that infected animal/plant and lost ability to reproduce independently. The higher organism protects them, and they provide energy for the organism - Endosymbiotic Theory.
6. We now know that certain diseases are the result of mitochondrial genes.

1. Found in plant.
2. Double membrane similar to mitochondria.
3. They also contain cytoplasm and stalk shaped structures in the chloroplast membrane called thyalkoids where the photosynthetic pigments are located (Chlorophyll A & B, etc.).

1. Endomembrane vesicles that contain specific enzymes. There are 2 types of microbodies: peroxisomes and glyoxysomes.
2. Peroxisomes

1. Transfer H+ atoms to 0₂ to form hydrogen peroxide. H₂0₂ - is toxic to cells (forms free radicals that damage DNA). Can be broken down by enzyme catalase.
2. Metabolize lipids.
3. Detoxify alcohols.

3. Glyoxysomes are found mostly in plant.

1. Associated with photosynthesis in leaves.
2. They convert oils in seeds to sugars to be used for nutrition.

1. A network of microtubules, intermediate tubules and actin filaments.
2. Helps to maintain cell shape much the way bones and muscles support animal structure.

1. Long thin filaments (in bundles) to form a meshwork within the cell.
2. Found in various locations with a variety of functions.
3. In plants, they form tracts or highways with which the chloroplast, etc. may travel (cytoplasmic streaming).
4. In intestine of humans, actin filaments make up the microvilli (fingerlike extensions) - that absorb nutrients.
5. Actin filaments in conjunction with myosin (motor proteins - dynenin, kinin) cause muscle contraction. Myosin has a head and tail portion. The tail is attached to membrane. The head reacts with ATP. As energy is released from ATP, it is used to link myosin with actin drawing muscle forward (contraction).
6. Actin filaments act as constriction ring to pinch off the 2 cells.
7. A layer of actin underneath the membrane of amoeba is responsible for the creeping movement of amoeba across surfaces.

1. Small hollow tubules made up of a globular protein called tubulin.
2. Extremely adaptable.
3. Helps to maintain cell shape as part of the Cytoskeleton.
4. Act as tracts for intracellular movement such as "spindles" in cell undergoing mitosis for movement of chromosomes to cell poles. In mitochondria, secretory vesicles, etc. move along microtubules.
5. Flagella and cilia - flagella are found on bacteria, some protozoa and sperm. Cilia are smaller, hair like appendages on protozoa and lining of body cavities (Ciliary Escalator - 2 mm/minute). Particles smaller than 50 m m should never enter lungs.

1. Ropelike assembly of polypeptides.
2. Support the nuclear envelope and the plasma membrane.
3. Also involved in formation of cell junctions.

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