3.2- Chapter 4- Transport across cell membranes Flashcards
What are cells surrounded by?
A cell surface membrane.
What additional membranes do eukaryotic cells have?
Internal membranes
What are membranes functions?
Membranes enable passage and control of the movement of substances across exchange surfaces
What do all membranes have?
The same basic structure.
What are membranes also known as?
Plasma membranes.
What does the cell surface membrane do?
- Surrounds the cell.
- Barrier between cytoplasm and environment.
- Establishes conditions inside and outside the cell.
What does partially permeable mean?
Allow some molecules through, but not others.
What do membranes around organelles do?
- Breaks the cell into different compartments and provide a barrier to the cytoplasm.
- e.g. ensures DNA doesn’t leave the nucleus
What are cell membranes composed of?
Phospholipids, proteins, glycoproteins, glycolipids and cholesterol.
What model describes the arrangement of molecules in the membrane and why?
- The fluid mosaic model.
- Fluid- The phospholipids form a bilayer that is constantly moving, making it flexible.
- Mosiaic- channel/ carrier protiens, glycolipids, glycoprotiens and cholersterol- scattered around bilayer- vary in size and shape and embedded like tiles.
Describe the bilayer.
- Continuous double layer.
- Hydrophobic tails point in.
- Hydrophilic heads face out.
What do most molecules not do across membranes and why?
Hint: To do with diffusion
Most molecules do not freely diffuse across membranes because they are:
1. Lipid insoluable- can’t pass bilayer
2. Too large to go through channel protiens
3. Same charge as channel protiens so repelled
4. Electrically charged (polar)- difficulty passing through non-polar hydrophoic tails
What are channel protiens specific to?
Different molecules
Label the pic of the cell membrane on page 2 of the question print out.
Answers on revision card
What do phospholipids form and how do they form it?
- Phospholipids form a bilayer
- Hydrophillic phosphate heads face outwards on both sides as attracted to water
- Hydrophobic fatty acid tails- point inwards towards the centre- repelled by water.
What does the phospholipid bilayer form a barrier to and what can freely diffuse across it?
- Forms a barrier to water soluble lipid insoluble substances. at the centre eg ions can’t diffuse through prevents them from entering and leaving the cell.
- Lipid soluble substances can enter and leave the cell.
- Small nonpolar lipid-soluble substances e.g. CO2 and water can diffuse through the cell.
What are the properties of the phospholipid bilayer?
- Flexible
- Self-sealing
- Constantly moving- fluid
Where can proteins be found within the bilayer?
- Embedded at the surface.
- Embedded one side to the other of the membrane.
What do proteins at the surface of the membrane do?
- Perform cell signalling- communication between cells.
- Provide mechanical support
- Act as receptor protiens to detect and respond to chemicals e.g. hormones- insulin- glucose absorbtion.
What do proteins that span one side of the membrane to the other do?
- Channel protiens- allow water-soluable ions to diffuse
- Carrier protiens- bind to large molecules e.g. glucose and amino acids and change shape to move them.
Describe the movement of proteins in the cell membrane.
Some protiens able to move side to side, others more fixed.
What are the overall functions of proteins in the cell membrane?
- Structural support
- Channels protiens for facilitated diffusion of water-soluable substances
- Carrier protiens for facilitated diffusion of large molecules and active transport.
- Cell identification (antigens)
- Cell-surface receptors
- Help cells adhere
What are glycoproteins?
Proteins with carbohydrates attached.
What the glycoproteins do in the cell membrane?
- Act as cell surface-receptors for hormones and neurotransmitters.
- Act as cell recognition sites (antigens), allowing cells to recognise each other, e.g. lymphocytes.
- Help cells attach to one another and form tissues.
What are glycolipids and where can they be found?
- Lipids with carbohydrates attached.
- Extend from the bilayer to outside the cell.
What the glycolipids do in the cell membrane?
- Act as cell surface receptors for chemicals
- Act as cell recognition sites
- Maintain the stability of the membrane
- Help cells attach to each other and form tissues.
Where is cholesterol found in the cell membrane and what is it?
- Embedded between phospholipids
- Present in all cell membranes except bacteria
- Type of lipid