Transport across cell membranes Flashcards
What are carrier proteins?
They bind to ions or molecules (glucose or amino acids) and change shape to move across the membrane and allow active transport
How does cholesterol reduce lateral movements of phospholipids?
Pull together fatty acid tails of phospholipids
How does cholesterol prevent leakage of water and dissolved ions?
Very hydrophobic
How do phospholipids remain rigid at high temperatures?
Cholesterol add strength to the membranes
How are glycolipids made?
Carbohydrate chain covalently bonded with a lipid
How do glycoproteins act as recognition sites?
Carbohydrate chain extend into watery environment outside the cell, where it acts as a receptor for specific cells
What are the components of the cell-surface membrane?
Phospholipids, proteins (carrier and channel), cholesterol, glycolipids and glycoproteins
How thick is the cell-surface membrane?
7nm
Why are cell-surface membranes described as fluid?
Individual phospholipids can move relative to one another, giving the membrane a flexible structure that is constantly changing shape
Why are cell-surface membranes described as mosaic?
The embedded proteins vary in shape, size and pattern that create a mosaic-looking image
What is diffusion defined as?
The net movement of molecules or ions from a region where they are more highly concentrated to one where their concentration is lower until evenly distributed
What molecules can diffuse easily across plasma membranes?
Small, non-polar molecules such as oxygen
What is facilitated diffusion?
Diffusion using transmembrane channels and carriers that span the membrane, e.g. carrier proteins and channel proteins
How do proteins channel select ions to move through?
Ions bind with the protein causing it to change shape in a way that closes one side and opens another
How do carrier proteins release molecules into membrane?
Specific molecules (glucose) will bind with different proteins that then change shape and release molecules
What is osmosis?
The passage of water from a region of high water potential to a region of low water potential through a selectively permeable membrane
What is water potential represented and what are the units?
The greek letter Psi
Kilopascals (kPa)
When is water potential 0?
Pure water at standard temperature and pressure (25C, 100kPa)
How do concentration and water potential link?
Higher concentrations lower the water potential
What is cotransport?
The coupled movement of substances across a cell membrane, by combining facilitated diffusion and active transport
How is active transport different from passive transport?
ATP is needed, against a concentration gradient, carrier protein molecules and highly selective
What are the functions of the phospholipid?
Allow lipid-soluble substances to cross, prevent water-soluble substances crossing and flexible and self-healing
What are the functions of glycolipids?
Act as recognition sites, maintain stability and help cells attach to form tissues
What are the functions of glycoproteins?
Recognition sites (hormones and neurotransmitters), help cells to form tissues and allows cells to recognise one another (lymphocytes)
