Membrane structure and functions Flashcards
List functions of membranes
They are important in cell signalling
They produce different compartments inside cells
They are partially permeable controlling what pases through them
Explain extrinsic proteins
They associate with the hydrophillic surfaces of the phospholipid bilayer
Explain intrinsic proteins
They lie within the phospholipid blayer, some of them are transmembranal and apiphatic
What is the roles of phospholipid in membranes
forms the bilayer which is the fundamental basis of the membrane in which all other components are embedded and provides a barrier to hydrophillic subtances.
What is the role of cholesterol in the cell membrane
It helps to maintain the fluidity of the membrane and stops it from being to stiff or fluid based on temperature
What are the roles of proteins and glycoproteins in the cell mebrane
- forms chanells through which hydrophillic substances can pass; the channells can be opened and closed
- act as transporters that can move substances across the membrane up their concentration graidients with the use of ATP
- Act as enzymes
- bind to proteins in neighboring cell membranes, holding the cells together
Explain the fluid mosaic model
Fluid refers to the fact that the molecules in the membrane are in constant motion, moving around within their own phospholipid monolayer, the term ‘mosaic’ refers to the way the membrane would look if viewed from above
Explain facillitated diffusion
Pathways provided by channel proteins lie in the membrane allowing ions (charged molecules) to pass through
Explain exocytosis
This is the movement of substances outside the cell mebrane it occurs when a vessicle containing the substance moves towards the plasma membrane, then joins with the plasma membrane and the contents of the vessicle is now released
Explain endocytosis
This is the movement of substances into a cell, during this process the cell spreads around the object outside the cell, the area enclised then becomes a vessicle, the contents of the vessicle is then absorbed into the cytoplasm
Structure of DNA
- A phosphate group;
-the five carbon sugar deoxyribose - an organic base
revise the components of a nucleotide in dna
.
Explain Transcription
It is the production of an mRNA molecule that has a complementary base sequence to one strand of a length of DNA, usually, only a small part of a DNA molecule is transcribed at one time
Explain translation
It is the process by which the code for making the protein - now carried by th mRNA molecule - is used to line up amino acids in a particular sequence and link them together to make a polypeptide.
Briefly explain the steps in mitosis
Prophase - The stage in which chromosomes become visble. As prophase proceeds the nucleolus dissappears. It is also at this stagethat the spindle begins to form. The centrioles move away from each other to opposite ends of the cell .
