HL 1 Biology

3.2 & 7.5 Proteins

<<Amino Acids and Proteins>>

Amino acids: the “R’ group can range from non-polar to polar (positively or negatively charged)

  • E.g. Serine, glutamic acid, alanine, glycine
  • Peptide Bond: bond between two amino acids in a dipeptide
  • Condensation: amino acids fuse together by reaction
  • Hydrolysis: amino acids are separated by reaction

Protein shapes categorized in fibrous and globular.

Fibrous proteins: elongated shapes, insoluble in water, physically tough

  • e.g. collagen in skin, keratin in hair/fingernails

Globular proteins: compact, rounded, usually water-soluble

  • e.g. enzymes/other functional proteins like antibodies

Protein functions:

  • proteins are water soluble if outer surface consists of polar amino acids. (non-polar amino acids of globular protein helps stabilize structure)
  • Proteins position controlled by the distribution of polar + non-polar amino acids on the surface of the membrane
  • Channel proteins (that enable facilitated diffusion of ions/polar molecules through membrane) have polar amino acids lining the pore where the particles diffuse
  • The specificity of the enzyme is determined from the amino acids forming in the active site of an enzyme

Primary and Secondary Structure:

  • Polypeptide: chain of amino acids
      • 20 commonly occurring amino acids are able to combine in any sequence
  • Secondary structures: the shape of the
      • formed as the chain of amino acid in a polypeptide has a polar covalent bond and tend to fold by hydrogen bonds.

Tertiary Structure: the three-dimensional shape of the protein

  • Formed from the R-groups interactions wand with the surrounding water medium
  • Types of interactions:
      • positively charged R-groups = interact with negatively charged R-groups
      • hydrophilic amino acids orientate towards water, hydrophilic amino acids orientate themselves outwards
      • polar R-groups form hydrogen bonds with other polar R groups
      • R-group so f amino acid cysteine can form covalent bond with R-group of another cysteine = forming a disulfide bridge

Quaternary Structure: the way polypeptides, fit together when there’s more than one chain

  • exposure to high temperatures, changes in pH cause alternations in structure of a protein (disrupts biological activity)
  • Protein is denatured when permanently lost its structure


Chapter 4 Questions (p.57)

1 (a) Protein and polypeptide can be the same if the protein only consists of one polypeptide. Majority of proteins are made of many polypeptides. (b) Although both are triglycerides, the fat is a solid at room temperature whereas the oil is in the form of a liquid. (c) Starch and glycogen are both polymers of glucose, yet starch is stored in plant cells where as glycogen is stored in animals. (d) Condensation is the process to give out water molecule as for the hydrolysis takes in water in order to separate the polymers to break apart. (e) Hydrophobic repels the water while hydrophilic is attracted to water.

2 (a) Hydrolysis of maltose: maltose + water –> glucose + glucose

(b) The condensation reaction that forms a triglyceride: 3 fatty acids + glycerol –> triglyceride + 3H20

(c) Hydrolysis of starch to remove a single molecule: starch with x glucose molecules + H20  –> starch with x-1 glucose molecules + glucose

3 The transparency of water to life is important because it is essential for underwater plants to undergo a process of photosynthesis as these plants or algae are the base of the food chain underwater. Also, this transparency helps these aquatic organisms to search for prey in the water life.

4 (a) Zeta globin, epsilon

(b) The gamma-globin gene is visible in the first 10 weeks of the gestation while the beta-globin has not yet been composed. The gamma-globin continues to decline while the beta-globin increases. Gamma-globin starts to decline and soon is not expressed after 6 months of age while the beta-globin increases and is expressed at 6 months of age.

(c) At 10 weeks of gestation, the hemoglobin has an equal amount of apha-globin and gamma-globin. Yet at 6 months of age, there is a larger amount of  alpha globin compared to the beta-globin in the hemoglobin.

(d) The source of oxygen for the fetus: maternal blood

(e) During the development and after birth, there is a change in the hemoglobin due to  the different affinity for oxygen between the fetal and maternal blood, the preparation for the fetus to perform an individual gas change, gives fetal blood more affinity (thus oxygen transition from mother to fetus).

6 (a) One type of secondary structure of a protein: α-helix

(b) Globular protein are those that are with the metabolic functions and often is water soluble, example includes hemoglobin and fibrous protein include keratin, which consists of non-polar amino acids.

(c) The polar amino acids help the determine the tertiary structure and chooses which domains of the protein will be found at the membrane’s surface. Also, the polar amino acids in the protein will place towards the water.

(d) α-helix and ß-pleated sheet are examples of secondary structure pattern, which  is a pattern of regular folding. These α-helix are stabilized by hydrogen bonds. The tertiary structure is determined by the hydrophobic interactions and are in a three dimensional shape, as well.

7 (a) The relationship between the water content at planting time and protein content is the following: when the quantity of water rises, the percentage of the grain protein decreases.

(b) This relationship exists because of the optimum level of water. In soil air, the optimum level is most likely to reduce and prevent nitrogen fixation.

8 The pH declines because of the process in which the fatty acids are released when the triglycerides are broken down. This fatty acid declines the pH.


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