Cells 2 Flashcards
What are all the parts of the cell membrane?
Glycoprotein, glycolipid, cholesterol, extrinsic protein, intrinsic protein, hydrophobic tail, hydrophilic head
What are the functions of the proteins in cell membrane?
- Provide structural support
- Act as carriers, transporting water-soluble substances across the membrane
- Allow active transport across the membrane by forming ion channels for sodium, potassium etc
- Form recognition sites by identifying cells
- Help cells adhere together
- Act as receptors e.g. for hormones
What is simple diffusion?
The NET movement of ions or molecules down their concentration gradient
What are the factors that affect the rate of diffusion?
- Concentration geadient
- Area over which diffusion takes place
- Thickness of exchange surface
How do you calculate the rate of diffusion?
Rate of diffusion = (surface area × difference in concentration gradient) / length of diffusion path
What is the law that the rate of diffusion is derived from?
Fick’s Law
What is facilitated diffusion?
Diffusion that uses both protein channels and carrier proteins
How do protein channels work?
Water soluble ions, glucose, amino acids and molecules which would diffuse slowly through the phospholipid bilayer pass through protein channels. The channels are selective and only open when specific molecules are present
Do either simple or facilitated diffusion require energy?
No
What is osmosis?
The passage of water from a region where it has a higher water potential to a region where is has lower water potential through a partially permeable membrane
What is water potential and what is it measured in?
The pressure created by water molecules
Measured in kPa
How does water move?
From a less negative water potential to a more negative water potential
What is the water potential of pure water?
0, so any solution must always be less than 0
What is a hypotonic solution?
A solution with a higher water potential compared with the inside of the cell
What is a hypertonic solution?
A solution with a lower water potential compared with the inside of the cell
What is an isotonic solution?
If two solutions have the same water potential
What will happen to a cell placed in a hypotonic solution?
It will grow and turn turgid
What will happen to a plant cell placed in a hypertonic solution?
It will shrink and become plasmolysed
What will happen to an animal cell placed in a hypertonic solution?
It will shrink and become flaccid
What is active transport?
The movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration using energy (ATP) and carrier molecules (proteins)
What do cells need to carry out active transport?
- Lots of mitochondria
- Good supply of ATP
- A respitory rate
- Many proteins in the membrane
How does a carrier protein work?
- The carrier proteins accept the molecules which bind to receptors on the channels of the carrier protein
- Inside the membrane ATP binds to the protein, causing it to split into ADP and a phosphate
- The protein molecule changes shape and opens to the opposite side of the membrane
- The molecules are then released to the other side of the membrane
- The phosphate molecule is released from the protein and recombines with ADP to form ATP
- This causes the protein to revert to its original shape and the process repeats
What does a co-transporter do?
It uses the concentration gradient of one molecule to move another molecule against its concentration gradient
What is the process of cotransport with a sodium potassium pump?
- The sodium potassium pump moves sodium out of the cell and potassium into the cell
- There is therefore a high concentration of sodium ions outside the cell which will diffuse back in
- At the same time the sodium diffuses back into the cell, it couples with glucose which is carried with the sodium
- This is an indirect form of active transport, as glucose is being transported against its concentration gradient
What is cotransport?
The movement of glucose into cells
What is an example of when the body uses cotransport?
In the ileum in the small intestine
