2.1 (b) - Cell Membrane Flashcards
1
Q
What is the cell membrane?
A
- The cell membrane, also known as the plasma membrane, is a double layer of lipids and proteins that surrounds a cell and separates the cytoplasm
2
Q
What is the structure of the cell membrane?
A
- Cell membranes consist of: Two layers (bi-layers) of phospholipid molecules; also know as the phospholipid bilayer.
- Very thin
- Fluid-mosaic model
- Proteins molecules embedded or attached.
3
Q
What is the function of the cell membrane?
A
- The cell membrane separates the cell from it’s surroundings and controls the exchange of materials in and out of the cell, as well as having a range of other important roles in cell communication, cell adhesion and the binding of hormones.
- Separate contents of cell from external environment
- Regulate passage of substances in/out of cell
- Cell recognition (e.g. other cells and hormones)
- Enable attachment of cytoskeleton
4
Q
What are Phospholipids?
A
- single molecules made up of two parts: a hydrophilic tail and two hydrophobic heads.
5
Q
What are the two types of membrane proteins?
A
- Integral Proteins
- Peripheral Proteins
6
Q
What are Integral proteins?
A
- Proteins which are permanently in the bilayer.
7
Q
What are Peripheral proteins?
A
- Proteins which tend to move more temporarily and are not a permanent part of the membrane.
8
Q
Where is Cholesterol located?
A
- Usually found positioned between the phospholipids (only in animal cells)
9
Q
What are Glycoproteins?
A
- Membrane proteins with carbohydrate chains attached.
10
Q
What are Glycolipids?
A
- Phospholipids with carbohydrate chains attached.
11
Q
What is the Fluid Mosaic Model?
A
- Used to describe the cell membrane, and contains, large proteins and glycoprotein molecules embedded in the phospholipid bilayer.
The molecules are able to move relative to each other.
12
Q
What does Permeable mean?
A
- Anything can pass through the cell membrane.
13
Q
What does Semi-Permeable mean?
A
- Only some things can pass through the cell membrane.
14
Q
What does Selectively Permeable mean?
A
- The cell membrane can regulate what passes through it.
15
Q
How is the Phospholipid Bilayer arranged?
A
- The phospholipid bilayer consists of two layers of lipid molecules which are arranged with their phosphate groups (Hydrophobic Tail) on the outside eg. Facing the outside of the cell and towards the cytoplasm and the lipid tails projecting inwards.
16
Q
What is the phosphate head called?
A
- The phosphate head of the phospholipid are known as Hydrophilic and have a
‘polar’ charge associated and therefore, they can interact with (or attract water molecules)
17
Q
What is the phosphate tail called?
A
- The phosphate tail are know as Hydrophobic and have a ‘non-polar’ charge associated and therefore do not interact with water (or they repel water.)
18
Q
What types of proteins are associated with the cell membrane?
A
- Channel proteins that are throughout the membrane which transport substances.
- Receptor proteins that are bound to the surface of the membrane and communicate to other parts through cellular communication.
- Proteins on the underside of the membrane with transfer message through intracellular signalling.
19
Q
What are the five functions of membrane proteins?
A
- Hormone Binding Site
- Cell Communication
- Cell Adhesion
- Channel Proteins and Pump Proteins
- Cholesterol
20
Q
What is the Hormone Binding Site?
A
- Hormones are molecules that carry messages to cell. some hormones are proteins and therefore, cannot cross the cell membrane.
- Many hormones transported in the blood can only bind and act on cells with complementary protein receptors on the outside of their membranes. Eg. A growth hormone molecule will only bind to a specific growth hormone receptor.
21
Q
How does Hormone binding occur?
A
- Protein receptors on the outside of the cell membrane have a shape which is complementary to the hormone. Eg. Lock and key fit.
- The binding of the hormone to the receptor triggers a signal sent inside the cell.
- This initiates cellular changes and gene activity. Eg. Human growth hormone stimulates growth, especially in childhood, strengthening bones and increasing muscle mass.
22
Q
How does Cell Communication occur?
A
- Cell communication can occur via direct contact between cell membrane proteins of adjacent cells or via hormones or nerve transmitter chemicals (called neurotransmitters)
- Proteins on the cell surface can send a signal to other cells when there is direct contact between the cells.
23
Q
How does Cell Adhesion occur?
A
- Integral proteins can stick out and bind to specific protein molecules on adjacent cells or attach to the cytoskeleton.
24
Q
What is the Cytoskeleton?
A
- The cytoskeleton is a framework of tiny protein tubules and filaments that extend throughout the cytosol.
- Its function includes attachment and movement of organelles, and movements of the cell membrane and chromosomes.
25
What are Channel Proteins and Pump Proteins?
- These proteins can either allow movement of molecules by proteins by diffusion or use energy to actively move molecules in and out of cells (active transport.) and allows the movement of molecules which are unable to diffuse through the phospholipid bilayer to diffuse through the protein (eg. Water molecules moving through a type of protein channel called aquaporin, where the channel regulates the flow of water in and out of the cell by a process called osmosis.
26
What is Cholesterol?
- Cholesterol is NOT a protein.
- The cell membranes within animal cells contain a lipid called cholesterol which is an important molecules in regulating the fluidity of the phosphates.
