2.1.5 Biological Membranes Flashcards
What is the role of the cell surface membrane?
To control which substances leave and enter the cell by being partially permeable. It separates the cells components from the external environment.
What are the functions of the Cell surface membrane?
Regulates the transport of materials into and out of the cell. Contains enzymes that are used in metabolic pathways. Has antigens so the immune system doesn’t attack it. May release chemicals to communicate with other cells via cell signaling. Has receptors to receive chemical signals. The site of many chemical reactions.
What is the role of membranes within cells?
Divide the cell into different compartments - called organelles and separates their contents from the cytoplasm of the cell.
What are the advantages of organelle membranes?
Separates the contents of the organelle from the rest of the cell so that all the substances needed for a process (e.g. respiration) are contained close together to make the process more effective.
What can organelle membranes do to transport molecules?
Can form vesicals
How are the membranes of mitochondria adapted?
Have a large surface area and are folded
How are the membranes of chloroplast adapted?
Contain chlorophyll for photosynthesis.
How are the membrane of intestines adapted?
Contain Digestive Enzymes
What is the membrane described as?
A phospholipid bilayer
Why is it a bilayer?
There are two layers of phospholipids
What is the structure of a phospholipid?
A hydrophilic phospholipid head. With two hydrophobic fatty acid tails.
What is the structure of a phospholipid bylayer?
Two layers of phospholipids with the heads facing outwards and the tails facing inwards. The tails are held together through hydrophobic interactions.
What is the fluid mosaic model?
The model that shows how the membrane is made up and how it is structured.
Why is it a fluid mosaic model?
Fluid - the phospholipids of the bilayer are constantly moving. So the membrane is flexible and can change shape.
Mosaic - There are lots of molecules such as proteins
What makes up the cell surface membrane?
Phospholipid Bilayer. Cholesterol. Glycoproteins. Glycolipids. Protein Receptor Sites. Channel Proteins. Carrier Proteins.
Where is cholesterol found?
Found in every cell membrane except bacteria. They fit between the phospholipids and bind between the hydrophobic tails.
What does cholesterol do?
Increases the packing of the membrane making is stronger and more rigid so its less likely to get damaged.
What effect does cholesterol have at high temperatures?
Prevents the membrane getting too fluid at warm temperatures as they maintain the placing
What effect does cholesterol have at cold temperatures?
prevents the membrane becoming rigid at cold temperatures by preventing the phospholipids packing too close together
What are intrinsic proteins?
They span the membrane from one side to the other. they have hydrophobic amino acids on the outside to interact with the hydrophobic layers of the bilayer.
What are Extrinsic proteins?
Peripheral proteins are present in one side of the membrane.
What are channel proteins?
Transport proteins that have a hydrophilic channel that certain charged or water soluble molecules/ions use as a passage through the membrane by facilitated diffusion.
What is the structure of a channel protein?
inside is lined with hydrophilic amino acids and filled with water molecules
What are carrier proteins?
Proteins that move large molecules through the membrane down the concentration gradient.
How do molecules pass through channel proteins?
Molecules bind to the protein causing a conformational change of the tertiary structure that forces the molecule through the membrane
What roles do Extrinsic proteins have?
Some attach to intrinsic proteins. Some help to maintain the structure. Some act as enzymes. Some are receptor sites for hormones. Some form glycoproteins
What are glycoproteins?
Proteins with a carbohydrate molecule attached.
What do glycoproteins do?
Allow cells to attach to each other and form tissues. Present antigens to T cells in the immune system. Receptors for hormones.
Where else can carbohydrate chains attach to?
lipids
What are lipids with carbohydrate chains called?
glycolipids
What are the roles of glycolipids?
Cell recognition
What is diffusion?
The net movement of particles (molecules or ions) from an are of high concentration to an area of low concentration.
How does the movement of molecules change during diffusion?
Molecules are always moving in all directions and will diffuse both ways. But the net movement will be from a high to low concentration.
What is equilibrium?
When the concentration of something both inside and outside the cell are the same.
Does diffusion require energy?
No
What molecules can diffuse through the membranes?
small non-polar molecules diffuse between phospholipids.
Water - Despite being Polar
What is the rate of diffusion dependant on?
The concentration gradient - the higher the gradient the faster the rate.
What is facilitated diffusion?
The diffusing of hydrophilic molecules across the membrane via protein molecules. This means that the molecules can pass through without interacting with the phospholipids.
What facilitates facilitated diffusion?
Carrier Proteins. Channel Proteins.
What is osmosis?
The movement of water from a region of higher water potential to an area of lower water potential through a partially permeable membrane.
What is water potential?
When water molecules collide with a membrane they exert a small force. This force adds up to form the water potential.
What is the symbol for water potential?
ψ
What is the unit for Water Potential?
KPa
What is the water potential of pure water?
0 KPa
What is active transport?
the movement of ions or molecules across a cell membrane from an area of lower concentration to a region of higher concentration
How does active transport take place?
The molecule to be transported attaches to a receptor site on a carrier protein - on the side with a lower concentration. A molecule of ATP binds to the carrier The phosphate attaches to the carrier protein and causes it to change shape. The ATP undergoes hydrolysis to produce a phosphate (Pi) group and ADP. This means that the protein moves the molecule from one side of the membrane to the other protein where it is released. The phosphate leaves and it returns to its original shape.
What is endocytosis?
Particles and molecules move into the cell through the fusion of the cell membrane to produce a vacuole.
What is exocytosis?
a process by which the contents of a cell vacuole are released to the exterior through fusion of the vacuole membrane with the cell membrane.
What is the need for endocytosis and exocytosis?
Larger molecules - such as proteins and bacteria - are too large to pass through the membrane by facilitated diffusion or active transport.
What happens during endocytosis?
The cell surface membrane folds in on itself to form a cavity around the substance to be endocytosed. This is called invagination. The membrane completely encircles the particle to make a vesical that gets pinched off. At this point
What happens to a substance after it is endocytosed?
It moves to the place that it is needed and released from the vesical.
What happens to bacteria after it is endocytosed?
Bacterial vesical is destroyed by lysosomes and the products are taken to where thy can be used by the cell
What is the endocytosis of a solid known as?
Phagocytosis
What is the endocytosis of a liquid known as?
Pinocytosis
What happens during Exocytosis?
Vesicles containing a substance move towards the cell surface membrane. The vesical fuses to the membrane and opens up with the substance now on the outside.
Is endocytosis and exocytosis a passive or active process?
Active.
Both Require energy from ATP.
