AQA Year 1 A Level Biology- Membranes and Proteins + Enzymes

• Enzymes are made up of long chains of amino acids that fold into complex three-dimensional structures.
• The active site of an enzyme has a specific shape that fits only one type of molecule, called its substrate.
• Enzyme-substrate complex is formed when the substrate binds to an enzyme.
• A catalyst speeds up chemical reactions by lowering the activation energy required for them to occur.
• What are membranes made out of?

  Phospholipid bilayer
• What are glycoproteins made out of?

  Proteins and carbohydrates
• What other molecule does the cell membrane contain?

  Chloresterol
• Why is the phosphate head hydrophilic?

  it is negatively charged, so is polar.
• Why are the fatty acid tails hydrophobic?

  uncharged, and non-polar, so can't form H bonds with H20
• True or False: Anything polar is soluble in water.

  True
• Why do phospholipids form a cluster when dropped in H20?

  Tails are hydrophobic so try to get away from water, hence a cluster being formed.
• Why on a TEM micrograph does the cell membrane appear as two dark lines?

  The dark lines are the hydrophilic heads which have been coated in heavy metal and therefore reflect electrons. The gap between hydrophobic tails have not been coated in heavy metal, so electrons pass through, and the hydrophobic tails do not show in the micrograph.
• What is the loop found inside proteins which are embedded inside the membrane called?

  Polypeptide chain
• Where are integral membrane proteins found?

  Embedded inside the membrane, next to phospholipid tails
• Where are transmembrane proteins found?

  across the whole membrane
• Where are peripheral membrane proteins found?

  attached to another protein which is embedded in the membrane
• What is the overall charge on an embedded protein?

  Neutral
• How can a protein be half-polar and half non-polar

  By having amino acids with polar or non-polar R groups in different areas.
• What do carrier proteins do?

  move molecules across membrane
• What do pump proteins do?

  Move molecules against a concentration gradient
• What is an example of a pump protein system found in the body?

  Sodium-potassium pump
• What do receptor proteins do?

  Detect molecules arriving at the cell membrane or that fit into their binding site.
• If a membrane has more chloresterol, what does this mean?

  It is more rigid
• What is the description of membrane structure called?

  Fluid Mosaic Model
• Give an example of a molecule found embedded in the thylakoid membranes.

  Chlorophyll
• What does chloresterol do to the cell membrane?

  Decreases fluidity and viscoscity
• Where in the phospholipid bilayer are the hydrophobic tails found? Knowing this, where are the hydrophilic heads found?

  hydrophobic tails = on the inside of the cell hydrophilic heads = on the outside of the cell
• What does hydrophilic mean?

  water loving
• What does hydrophobic mean?

  water hating
• If a part of a protein is found near the fatty acid tails, will that part be polar or non-polar?

  Non-polar
• If a part of a protein is found near the hydrophilic phosphate heads, will that part be polar or non-polar?

  Polar
• Name a cell organelle which is made up of phospholipids.

  Golgi vesicles
• What are the monomers of proteins?

  amino acids
• What is the amine group in an amino acid?

  NH2
• What is the carboxyl group in an amino acid?

  COOH
• What is the R group in an amino acid?

  A variable group
• What is the R group in glycine?

  H
• How many different amino acids are there?

  20
• How many different R groups are there?

  20
• Name the key components of an amino acid.

  Amine (NH2) group, carboxyl (COOH) group, Central carbon atom, central hydrogen atom bound to carbon atom