Cell Biology Flashcards
What is the chemical composition of the IDEALISED cell, and what are those chemicals used for?
Water and electrolytes (70-85%). No water, no life, but it includes electrolytes (K+, Mg++, P, S, HCO3)
Protein (10-20%). Structure and function
Carbohydrate (<1%) Nutrition and energy Storage
Lipid (2%) Structure and energy Storage
Describe the structure of a cell membrane
The cell membrane is a phospholipid bi-layer. This is two layers of ampiphylitic phospholipids, with the hydrophobic ends as the ‘meat in the sandwich’. The membrane is scattered with proteins (floating on lipid rafts) that allow various ions and molecules to pass through.
What are the functions of a cell membrane
The cell membrane has three functions:
1 - interface (moving objects in and out)
2 - compartmentalisation
3 - providing surface area for reactions
What are the six basic functions of a cell membrane’s (plasmalemma’s) integral proteins?
1 - Active transporters - to move molecules/ions against a concentration gradient.
2 - passive transporters - to move molecules/ions with a concentration gradient
3 - receptors - recognition points that bond ligands (messaging molecules) including hormones
4 - linker proteins - that anchor the cell to teh extra-cellular matrix
5 - enzymes - to catalyse reactions
6 - Structural proteins - to attach to neighbouring cells (even cytoplasm may be shared in some cases).
Describe the cell nucleus
The nucleus is the largest organelle within the cell, and is often visible on light microscopy. it is bounded by a nuclear envelope of two adjoining bi-layers, passage across which is governed by the nuclear pore complex.
The nucleus will often contain a nucleolus, one of the densest areas in the cell, with aggregations of ribosomal RNA.
Describe the endoplasmic reticulum
The ER is a network of interconnected tubules throughout the cytoplasm. The rough ER has ribosomes attached, and is dedicated to the synthesis of protein. The smooth ER does not have ribosomes attached, and is dedicated to synthesising lipids and other metabolic functions.
Describe the position and function of the Golgi Apparatus
The Golgi Apparatus is in close proximity to the Rough ER - primarily to have easy access to proteins. The function of the GA depends on the type of molecule it encounters -
Proteins are modified via glycosylation or phosphorylation (“putting on the jewellery”) and packed into granules for export or secretion. Modification often includes a signal to direct the protein to its destination, and adds function that did not previously exist, converting them into proteoglycans.
Carbohydrates are synthesised into sialic acid or galactose, which can be used to form proteoglycans.
The GA can also assemble new membranes for use within the cell.
Are cells ‘fixed units’ until they die?
No. The components in a cell are constantly being renewed and recycled, with old parts being replaced.
What is the function of a lysosome?
Lysosomes act as the garbage dump of the cell - they have a low pH, and contain hydrolytic enzymes that can break down degraded membranes and extra-cellular material. if a lysosome’s membrane degrades, it can digest the cell itself.
What is the cause and outcome of a lysosome storage disorder?
Lysosome storage disorders are the result of an enzyme deficiency. They result in the accumulation of a product that would normally be broken down.
What is the function of a peroxasome
The peroxasome functions similar to a lysosome in that it breaks down material (including conducting initial catabolism of long-chain fatty acids). However a preoxasome uses oxidative enzymes, rather than hydrolytic enzymes, so has an end-product of hydrogren peroxide.
Describe the mitochondria
Mitochondria are present in all cells except red blood cells. Their primary function is cellular respiration and ATP production, and they contain DNA that is distinct from the rest of the cell.
The quantity of mitochondria is dependent on the energy requirements of the cell, and they are self-replicative (independent of the rest of the cell).
Mitochondria contain a double membrane, with the inner membrane folded into CHRISTAE to increase the surface area. Oxidative phosphorylation and ATP synthesis are conducted on the inner membrane.
What is the cause and outcome of a mitochondrial disorder?
Mitochondrial disease results in the absence of certain enzymes that are produced by the mitochondrial DNA, which cannot be replicated by nuclear DNA.
