Back to AI Flashcard MakerBiology /OCR Biology A - 2.1.5 - Biological Membranes Part 2
Carrier protein
Changes shape to allow specific molecules in and out of the cell
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Key Terms
Term
Definition
Carrier protein
Changes shape to allow specific molecules in and out of the cell
Channel protein
These provide a hydrophilic channel that allows the passive movement of polar molecules down a concentration gradient Water filled channel inside is l...
Integral/ intrinsic proteins
Proteins that span the whole membrane Either channel or carrier proteins
Protein receptor site
Acts as receptors to detect hormones and/or drugs
How do carrier proteins work
Molecule binds Carrier protein changes shape Releases molecules on the other side
When is diffusion rapid
Small | Non-polar molecules
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| Term | Definition |
|---|---|
Carrier protein | Changes shape to allow specific molecules in and out of the cell |
Channel protein | These provide a hydrophilic channel that allows the passive movement of polar molecules down a concentration gradient Water filled channel inside is lined with hydrophilic amino acids |
Integral/ intrinsic proteins | Proteins that span the whole membrane Either channel or carrier proteins |
Protein receptor site | Acts as receptors to detect hormones and/or drugs |
How do carrier proteins work | Molecule binds Carrier protein changes shape Releases molecules on the other side |
When is diffusion rapid | Small | Non-polar molecules |
Facilitated diffusion | Involves carrier and channel proteins within the cell membrane. These help transport large, polar molecules e.g. glucose, across the membrane |
Functions of a cell membrane | Can be a site of chemical reactions - contain enzymes Cell signalling Create conc. gradient Has antigens so the immune system recognises it as ‘self’ Separates contents from outside - barrier (cell or organelles) Regulates transport of molecules in/out of a cell or organelle Seperates metabolic pathways |
Factors affecting diffusion | Temperature Molecule size Conc. gradient Diffusion distance Surface area |
Cell membrane permeability at higher temps | Phospholipids moving around so fluidity and permeability increases (more kinetic energy) Cholesterol reduces the fluidity The proteins could denature and the bilayer could be completely permeable |
What does water dissolve | Polar solutes |
What does ethanol dissolve | Membranes, disrupting cells which is why alcohols are used in antiseptic wipes |
How do solvents affect permeability | Non polar or less polar solutes will disrupt membranes as the tails no longer orientate towards the middle. The membrane will become more fluid and more permeable |
What happens if animal cells are put into pure water | Cell bursts open, it is cytolysed |
What happens if animal cells are put in a solution with low water potential | Cell shrinks and appears wrinkled - it is crenated |
What happens if a plant cell is put in pure water | Plant cell wall prevents bursting. Membrane pushes against cell wall - cell is turgid |
What happens if a plant cell is put in a solution with very low water potential | Plasma membrane pulls away from the cell - it is plasmalysed |
Water tendency | Measure of the tendency of water molecules to diffuse from one region to another Measured in kPa |
What is water potential affected by | The amount of solute it contains The greater the amount of solute it contains, the lower or more negative the lower water potential |
Osmosis | The passive movement of water from an area of high water potential to an area of low water potential across a partially permeable membrane |