Cell Flashcards
Ribosomes
Ribosomes are associated with the plasma membrane of a cell. they are about 15 nanometre to 20 NM in size and are made up of two sub units 50s and 30s units which when are present together form a 70s prokaryotic ribosomes. ribosome are the site of protein synthesis. several ribosomes May attach to a single and form a chain called poly ribosome or polyzome. the ribosome of a polyzome translate into proteins.
Inclusion bodies
Reserve material and prokaryotic cells are stored in the cytoplasm in the form of inclusion bodies. these are not bound by any membrane system and lie free in the cytoplasm. for example phosphate granules sinophyceen granules and glycogen granules. gas vacuoles are found in Blue Green and Purple and green photosynthetic bacteria
Eukaryotic cell
Eukaryotic cells include all the protest plants animals and fungi. In Eukaryotic cells there is an extensive compartmentalisation of cytoplasm through the presence of membrane bound organelles. Possess and organised nucleus with a nuclear envelope. They have a very complex locomotive and cyto skeletal structures genetic material is organised into chromosomes plant and animal cells are different as the former possessive cell walls plasters and large central vacuole which are absent in animal cells on the other hand animal cells have sensues which are absent in almost all plant cell
Cell membrane
the cell membrane is mainly composed of lipids and proteins.
The major lipids are phospholipids that are arranged in a bilayer.
the lipids are arranged within the membrane with the polar head towards the outer sides and the hydrophobic tails towards the inner part.
This ensures that the nonpolar tail of saturated hydrocarbons is protected from the aqueous environment. In addition to phospholipids membrane also contains cholesterol. biochemical investigation clearly revealed that the cell membranes also possess protein and
carbohydrate. The ratio of protein and lipid varies considerably in different cell types. In human beings, the membrane of the erythrocyte has approximately 52 per cent protein and 40 per cent lipids. Depending on the ease of extraction, membrane proteins can be classified as integral and peripheral.
Peripheral
proteins lie on the surface of membrane while the integral proteins are partially or totally buried in the membrane
fluid mosaic model
According to this, the quasi-fluid nature of lipid enables lateral movement of proteins within the overall bilayer.
This ability to move within the membrane is measured as its fluidity.
The fluid nature of the membrane is also important from the point of view of functions like cell growth, formation of intercellular junctions, secretion, endocytosis, cell division etc.
One of the most important functions of the plasma membrane is the transport of the molecules across it.
The membrane is selectively permeable to some molecules present on either side of it.
Many molecules can move briefly across the membrane without any requirement of energy and this is called the passive transport.
Neutral solutes may move across the membrane by the process of simple diffusion along the concentration gradient, i.e., from higher concentration to the lower.
passive transport.
Movement of molecules across the membrane without any requirement of energy
Fluidity
The ability to execute lateral movement of proteins within the overall bilayer due to the Quasi fluid nature of lipid is called fluidity.
The fluid nature of the membrane is also important from the point of view of functions like cell growth, formation of intercellular Junction, secretion, endocytosis, cell division etc
Osmosis
Movement of water across the membrane by diffusion is called osmosis
Active transport
As the polar molecules cannot pass through the nonpolar lipid bilayer, they require a carrier protein of the membrane to facilitate their transport across the membrane. A few ions or molecules are transported across the membrane against their concentration gradient, i.e., from lower to the higher concentration. transport is an energy dependent process, in which ATP is utilised and is called active transport, e.g.. Na+/K+ Pump.
Cell wall
a non-living rigid structure called the cell wall forms an outer covering for the plasma membrane of fungi and plants.
Cell wall not only gives shape to the cell and protects the cell from mechanical damage and infection, it
also helps in cell-to-cell interaction and provides barrier to undesirable macromolecules. Algae have cell wall, made of cellulose, galactans, mannans and minerals like calcium carbonate
in other plants it consists of cellulose, hemicellulose, pectins and proteins.
