cells test revision Flashcards
Explain how the phospholipid bilayer is made
hydrophilic heads due to negative charge on the phosphate group being attracted to water. and hydrophobic tails beings repelled by water. this means that that phospholipids spin around so that each tail is facing each other.
what is the structure of the cell membrane?
- fluid mosaic model due to the mixture and movement of phospholipids, proteins, glycoproteins and glycolipids it is made up of.
How is cholesterol an important component in the cell membrane?
- restricts the lateral movement of other molecules in the membrane. this makes the membrane less fluid at high temperatures and prevents water and dissolved ions from leaking out of the cell.
- acts a s a buffer for temperature changes.
- pull together fatty acid tails of phospholipids.
What are extrinsic (peripheral) proteins function?
- proteins that are just on the surface of the membrane
- they provide mechanical support or are connected to proteins or lipids to make glycoproteins and glycolipids.
What are intrinsic (integral) proteins function?
- the integral proteins are protein carries or channel proteins involved in the transport of molecules across the membrane.
- they are imbedded throughout the membrane
What are protein channels?
- protein channels are tubes that fill with water to enable water-soluble ions to diffuse.
- this is still selective as the channel proteins only open in the presence of certain ions.
What are carrier proteins?
- proteins that bind with other and larger molecules, such as glucose and amino acids and change shape to transport them to the other side.
What do we mean when we say the membrane is partially permeable?
-only lipid soluble substances and small molecules can pass through the membrane by diffusion.
What is simple diffusion?
The passive net movement of molecules from an area of higher concentration to an area of low concentration until equilibrium is reached. for this to happen the molecules must be lipid soluble and small.
What is facilitated diffusion?
The passive movement of ions and polar molecule s through a cell membrane using protein channels and carrier proteins. from a high conc. to a low conc.
What is osmosins?
the movement of water from an area of high water potential to an area of lower water potential across a partially permeable membrane.
What is water potential?
- the pressure created by water molecules
- measured in kPa
- pure water has a WP of 0 so when solutes are dissolved in water the water potential will become negative.
What is an isotonic solution?
a solution where the water potential is the same in the cell and in the solution
What is a Hypotonic solution?
a solution where the water potential is more positive that the cell so water moves in
What is a Hypertonic solution?
a solution where the water potential is more negative than inside the cell so water moves out
What is active transport?
The active movement of molecules in or out of a cell from an area of low concentration to an area of high concentration via carrier proteins and ATP
How does active transport happen?
- molecule binds to the carrier protein that has a complimentary receptor shape
- ATP binds to the carrier protein from the inside of the cell and is hydrolysed into ADP +Pi
- this caused the carrier protein to change shape and release the molecule to the other side.
- the phosphate ion is then released and the protein returns to its original shape
What happens in the co-transport of glucose and sodium ions in the ileum?
- sodium ions are actively transported out of the epithelia cell into the blood via the sodium /potassium pump
- this reduces the sodium ion concentration in the epithelial cell
- sodium ions can the diffuse from the lumen down the concentration gradient into the epithelial cell
- sodium diffuses through a cotransport protein so glucose attach to the cotransport protein and are brough into the epithelial cell against their concentration gradient.
- glucose then moves by facilitated diffusion from the epithelial cell into the blood.
What affects the rate of diffusion?
- an increased surface area of cells (micro villi)
- an increase in the number of protein channels and carrier proteins
- a short diffusion distance
- temperature
What are glycoproteins?
- extrinsic proteins that are associated with carbohydrates form glycoproteins
- their function is cell recognition in the form of antigens
- they help cells attach to one another and form tissues for mechanical strength
- they form receptors sites for hormones or neuro transmitters.
What are glycolipids?
- carbohydrates covalently bonded with lipids.
- they are used in cell recognition in the form of antigens
-they help cells attach to one another and form tissues for mechanical strength
