Biological molecules

• What is the nature of the membrane described?

  It is selectively permeable.
• Which types of molecules can move through the phospholipid bilayer?

  Small and non-polar molecules.
• What does the selective permeability of the membrane allow?

  It controls what goes in and out of the cell.
• What is digitals made from?

  It is made from steroids.
• What type of lipid is cholesterol?

  It is a steroid alcohol.
• How many carbon-based rings does cholesterol consist of?

  Four carbon-based rings.
• Where is cholesterol mainly made in animals?

  In the liver.
• How do plant sterols differ from cholesterol?

  They have different structures.
• What are some steroid hormones made from cholesterol?

  Testosterone, oestrogen, and vitamin D.
• Why can steroid hormones easily pass through the phospholipid membrane?

  Because they are small and non-polar.
• What is the difference between a triglyceride and a phospholipid?

  • Triglycerides: three fatty acids and glycerol
  • Phospholipids: two fatty acids, glycerol, and phosphate group
• How does the presence of a phosphate group affect lipid properties?

  It makes the lipid amphipathic.
• What type of reaction occurs when a phospholipid reacts with glycerol?

  A condensation reaction.
• Why do phospholipids form a bilayer in water?

  They are amphipathic and arrange themselves.
• What are the general structures of amino acids?

  • Central carbon atom
  • Amino group (-NH2)
  • Carboxyl group (-COOH)
  • R group (varies among amino acids)
• What are amino acids the monomers of?

  Proteins.
• What is a peptide bond?

  A bond formed between two amino acids.
• What do proteins primarily consist of?

  Long chains of amino acids.
• How do proteins function in living organisms?

  They form structural components and enzymes.
• How do animals obtain amino acids?

  From their food.
• What do plants need to make amino acids?

  Access to fixed nitrogen.
• What elements do amino acids contain?

  Carbon, hydrogen, oxygen, and nitrogen.
• How many different amino acids are there?

  Over 500, but 20 are protein.
• What does the R group in amino acids represent?

  It varies in each amino acid.
• What happens to the carboxyl group in acidic conditions?

  It produces H+ ions.
• What is the role of buffers in amino acids?

  They help resist changes in pH.
• What type of reaction forms a peptide bond?

  A condensation reaction.
• What type of reaction breaks a peptide bond?

  A hydrolysis reaction.
• What are the levels of protein structure?

  1. Primary structure: sequence of amino acids
  2. Secondary structure: coiling or folding (α-helix, β-pleated sheet)
  3. Tertiary structure: overall 3D shape
  4. Quaternary structure: multiple polypeptide chains
• What determines the function of a protein?

  The sequence of amino acids in its structure.
• What stabilizes the secondary structure of proteins?

  Hydrogen bonds between amino acids.
• What is the α-helix in protein structure?

  A common secondary structure formed by twisting.
• What is the β-pleated sheet in protein structure?

  A secondary structure formed by folding.
• What interactions contribute to tertiary structure?

  Hydrogen bonds, disulfide bridges, ionic bonds.
• What characterizes quaternary structure in proteins?

  Consists of more than one polypeptide chain.
• How many possible ways can 100 amino acids be ordered?

  $20^{100}$ possible ways.
• What happens to the shape of a protein if the amino acid sequence changes?

  The function of the protein may change.
• What stabilizes the α-helix structure?

  Hydrogen bonds between amino acids.
• What is the role of hydrogen bonds in protein structure?

  They stabilize secondary structures.
• What happens to polypeptide chains at optimal temperature and pH?

  They maintain stable secondary structures.