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HNC Cell Biology

LO1

QuestionAnswer
Describe the chemical structure of a phospolipid? glycerol molecule with two fatty acid chains attached at carbons 1 and 2 and phosphoric acid attached to carbon 3.
By what type of bond are is the phosphoric acid attached to glycerol in a phospholipid? phosphoric acid is attached to glycerol by an ester bond in a phospholipid.
How many carbon-carbon double bonds are present in a saturated fatty acid? none
How many carbon-carbon double bonds are present in an unsaturated fatty acid? 1 or more carbon-carbon double bonds
How do unsaturated fatty acids in phospholipids influence membrane fluidity? Double bond in unsaturated fatty acids causes a kink in the molecule preventing it from packing tightly. This makes membrane more fluid
How do saturated fatty acids in phospholipids influence membrane fluidity? Saturated fatty acid tails are straight so they can pack tightly. This maximises hydrophobic interactions between the molecules and makes the membrane less fluid.
What does a cholesterol molecule consist of? Four joined-up carbon rings. A, B, C rings have 6 carbon atoms while D has 5 carbon atoms
What is cholesterol a precursor for? Cholesterol is a precursor for making steroid hormones.
How does cholesterol influence membrane fluidity? Inflexible ring structure of cholesterol allows fatty acid chains to pack more tightly which reduces membrane fluidity
Why is membrane fluidity important for the cell? Allows the cell to assume variety of shapes, allows for efficient membrane repair, allows for transport of materials in and out of the cell
What processes is cell membrane involved with? cell adhesion, ion conductivity and cell signalling (communicating with other cells) . it can serve as the attachment surface for the cell wall and intracellular cytoskeleton
What is the cell membrane composed of? lipids and proteins
What is the most common type of lipid found in membranes? Phospholipids are the most common membrane lipids.
How are proteins and lipids arranged in the cell membrane? Proteins and lipids in a membrane form a two dimensional liquid bi-layer, which is asymmetric, with different molecules present at either side of the membrane
How do molecules diffuse within the phospholipid bilayer? Molecules diffuse laterally
Phospholipids are amphipathic. What does this mean? Phospholipids display affinity for both polar and nonpolar molecules
What are phospholipids composed of? Phospholipids are composed of a hydrophilic (water loving, polar) head and two hydrophobic (water-hating, nonpolar) fatty acid tails which are joined together by a glycerol molecule.
How many carbon atoms typically make up a fatty acid tail? Typical fatty acid tail is between 16 and 18 carbon atoms long.
What other types of lipids are present in cell membranes besides phospholipids? Glycolipids (such as sphingolipids) and sterols (such as cholesterol)
What molecule replaces glycerol in the structure of sphingolipid? Sphingosine
What role do sphingolipids play and where are they found? Sphingolipids are found on the outside face of the lipid bilayer and play an important role in cell recognition and signalling.
What is the most common sphingolipid in human cells and where is it found? Sphingomyelin is the most common type of sphingolipid in human cells. It is found in the myelin sheet that surrounds the nerve cell axons.
Why is cholesterol important in animal cell membranes? Cholesterol helps maintain membrane structural integrity and fluidity allowing them to exist without a cell wall, to be able to change shape and to move.
What force keeps the phospholipid bilayer together? Hydrophobic non-covalent interactions between the lipid tails are the force that holds the membrane together.
How are phospholipids arranged in a bilayer? hydrophobic "tail" regions of the phospholipid are away from water while the hydrophilic "head" regions are tightly packed together and in contact with water at both the intracellular and extracellular faces of the bilayer.
What characteristics of phospholipids influence the fluidity of the membrane? The length and the level of saturation of fatty acid tails
How does length of a phospholipid fatty acid tail influence the membrane fluidity? The longer the fatty acid tails are, the more surface is available for hydrophobic interactions which makes the membrane less fluid (more viscous).
How does a degree of fatty acid tail saturation influence the membrane fluidity? Saturated fatty acid tails pack tightly and make membrane less fluid. Unsaturated fatty acid tails pack loosely and make membrane more fluid.
What cell processes are membrane proteins involved in? transporting substances across the membrane, cell–cell contact, surface recognition, cytoskeleton attachment, cell signalling and enzymatic activity.
What does activity of a protein depend on and how is this achieved? Protein activity depends on proteins having a correct 3D shape which is achieved through correct folding and sometimes post-translational modifications
What are the three types of membrane proteins? Membrane proteins can be integral, lipid anchored and peripheral
Name some examples of integral membrane proteins? Ion channels, proton pumps, G protein-coupled receptor
Describe an integral membrane protein: Proteins spanning the membrane have hydrophobic domain that is in contact with hydrophobic fatty acid tails of lipids and hydrophilic domains that are in contact with phosphate heads and the outside or inside of the cell.
Name an example of lipid anchored protein? G proteins
Describe peripheral membrane proteins: Proteins that are temporarily attached to integral membrane proteins, or associated with peripheral regions of the lipid bilayer.
Name some examples of peripheral proteins? Some enzymes, some hormones
What are the main functions of integral membrane proteins? They can act as transport proteins, cell markers and receptor proteins
What is lipid bilayer permeable to? Lipid bilayer is permeable to small non polar molecules or dissolved gasses such as oxygen or carbon dioxide
How do large and/or polar molecules cross the lipid bilayer? Large and/or polar molecules move across the bilayer with help of integral membrane proteins which either form pores (holes) or act as pumps.
Created by: dr.prorocic
 

 



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