Biol 1057 - The cell and the membrane Flashcards
Outline the ideas in the modern cell theory
- All cells have the same basic chemical composition
- All cells use energy
- All cells genetic material that is duplicated ia passed on as each cell
divides
Outline the differences between prokaryotic and eukaroytic cells
P
* No nucleus
* Circular DNA as a single chromosome
* No organelles, just ribosomes
* Most are 0.2 μm – 2.0 μm
* Unicellular only
E
* Membrane bound nucleus
* Linear DNA organized into multiple chromosomes
* Membrane bound organelles
* Most are 5 μm – 100 μm
Outline the first type of cells
- The first group of cells in an embryo are all identical, unspecialized however become specialised after
Quick recap of cell organelles
Describe what is meant by the plasma membrane and define fluid mosaic model
- A selectively permeable barrier that separates the cell’s internal environment from its external surroundings
FLUID: phospholipids are free to
move within the layer
MOSAIC: : there are number of
proteins or other organic
molecules embedded in the
membrane
Describe the main component of cell membranes
Phospholipids aligned as a bilayer allows for movement
=Hydrophillic heads attracted to water
=Hydrophobic tails repelled by water
➢Allow lipid-soluble substances in
and out of the cell
➢Prevent water-soluble substances
to enter and leave the cell
Describe the 2 types of protein in the cell membrane & briefly outline function
PERIPHERAL PROTEIN
- Provide mechanical support
- OR Attached to proteins or lipids to form glycolipids & glycoproteins
- Involved in cell signalling, as receptors
INTEGRAL
- Either Channel or carrier protein
- Involved in the transport of molecules across the membrane
Describe the role of cholestrol in the cell membrane
- Restrict lateral movement of other molecules in the membrane which improves tability
- Therefore membrane less fluid at high temperatures
Describe what type of molecules can simply diffuse across the bilayer?
- Lipid soluble, Non-polar & Very small
Outline the factors affecting membrane structure
- Temperature: high temperature so more kinetic energy so more movement. Membrane becomes more fluid,
increased permeability. High temperatures denature proteins. - Solvents: organic solvents (alcohols, alkenes) dissolve membranes. Non-polar alcohol enters membrane
disrupting the structure.
Outline the difference between passive and active processes
- Passive processes - do not require external source of energy such as ATP
- Simple diffusion
- Facilitated diffusion
- Osmosis
- Active processes - require external source of energy such as ATP
- Primary
- Secondary / co-transport
- Vesicular transport
Define diffusion
- Diffusion is a passive process
- That involves the overall net movement of small molecules from a region of higher concentration to a lower concentration
- Down the concentration gradient, until equilibrium
Define Facilitated Diffusion
- Facilitated diffusion is a passive process
- That involves the overall net movement of molecules/ions from a region of higher concentration to a lower concentration
- Down the concentration gradient across a partially permeable membrane
- Via channel or carrier proteins
FOR CHARGED, POLAR AND LARGE MOLECULES
Define Osmosis
- Osmosis is a passive process
- That involves the overall net movement of water molecules
- From an area of high water potential to an area of low water potential down water potential gradient
- through a partially/selectively permeable membrane until equilibrium
Water travels freely across membranes through aquaporins.
Describe what is meant by tonicity
Tonicity of a solution relates to how the solution influences the shape of body cells.
- Tonicity affects the movement of water across membranes
Define Active Transport
- Active transport is an active process requiring ATP from respiration
- Which involves the movement of molecules/ions from an area of low concentration to a high concentration against the concentration gradient
- Across a cell membrane, using carrier proteins
Describe the process of active transport across a cell membrane.
- Complementary molecule to be transported binds to the specific site of carrier protein
- ATP on the inside of the membrane directly bonds to a carrier protein and hydrolysed to form ADP and Pi(phosphate)
- Causing carrier protein to change shape and move molecule across membrane & release
- Pi ion is released causing carrier protein to go back to its original shape
Define Co-transport
- Co-transport is the transport of one substance coupled with the transport of another substance across a semi permeable membrane
- Using a carrier protein
- Both molecules move in same direction against concentration gradient
Explain how Co- transport is involved in the absorption of glucose in the small intestine
ROUGH DIAGRAM:
LUMEN OF ILEUM \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ EPITHELIAL CELL \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ BLOOD
- Na+ ions are actively transported out of epithelial cells into bloodstream by carrier protein using hydrolysis of ATP
- So lower conc of Na+ ions in epithelial cell than lumen Generateing a concentration gradient for Na+ ions from ileum into epithelial cell
- Na+ ions move in by facilitated diffusion in co transporter bringing glucose with it against its concentration gradient
Outline what is meant by vesicular transport
GET DIAGRAM
Bulk Transport = required for large
molecules
* Exocytosis – the outward bulk transport of
molecules through the membrane
Vesicles containing materials fuse with the
membrane as secretion takes place
* Endocytosis – the inward bulk transport of
molecules through the membrane
A portion of the membrane engulfs a substance
