BSC2010 Lecture 13 Review

Practice Questions

  • Question: Which of the following amino acids is not commonly phosphorylated?

    • A. Tyrosine

    • B. Serine

    • C. Cysteine

    • D. Threonine

Allosteric Regulation of Enzyme Activity

  • Allosteric sites can be modified by:

    • Reversible covalent binding of a molecule

    • Phosphorylation: A phosphate group is added by a protein kinase on an amino acid residue (serine, threonine, or tyrosine).

    • If the modification occurs in a hydrophobic region, it may induce changes that affect interactions with hydrophilic regions of the enzyme.

    • Protein Phosphatases: Remove phosphate groups from proteins.

    • Significance of Phosphorylation: It is crucial for cells to regulate enzymes and other proteins.

R Group Modification Through Phosphorylation

  • Phosphorylated Amino Acids:

    • Serine: Phosphoserine

    • Threonine: Phosphothreonine

    • Tyrosine: Phosphotyrosine

  • Impact of R Group Modification:

    • The addition of a chemical group changes interactions with nearby amino acids, affecting the protein's shape.

The Twenty Common Amino Acids

  • Grouped according to properties conferred by their side chains:

    • Differences in charge, polarity, size, shape, and functional groups lead to structural diversity and specificity in interactions.

  • Examples of Amino Acids:

    • Glycine: Small, fits into tight corners.

    • Proline: Forms a covalent bond with its hydrocarbon side chain causing a ring structure, which stabilizes bends or loops in proteins.

Formation of Disulfide Bonds

  • Cysteine:

    • Contains a terminal sulfhydryl (─SH) group that can react with another cysteine side chain to form a disulfide bridge or disulfide bond (─S─S─).

    • Function: Stabilization of the three-dimensional structure of proteins.

Primary Active Transport

  • Definition: Involves the direct hydrolysis of ATP for energy.

  • Sodium-Potassium Pump (Na+-K+ Pump):

    • Moves Na+ out of a cell while bringing K+ in.

    • For every molecule of ATP consumed, 3 Na+ ions are pumped out, and 2 K+ ions are pumped in, maintaining concentration gradients.

Differences Between Active and Passive Transport

  • Active Transport: Requires energy input, moves substances against their concentration gradients via carrier proteins.

  • Passive Transport: Does not require energy, substances move down their concentration gradients.

Signal Transduction and Cellular Response

  • Concept Overview:

    • Cells can detect and respond to signals through specific receptors.

    • Signals can promote various cellular responses such as opening ion channels or altering enzyme activity.

Signal Amplification

  • The cascade of cellular events during signal transduction increases the amplification and distribution of the initial signal.

Cellular Respiration

  • Inputs for Cellular Respiration:

    • Glucose and oxygen are the main inputs.

  • ATP Production: A single glucose molecule can yield approximately 30 to 32 ATP during aerobic respiration, involving glycolysis, pyruvate oxidation, the citric acid cycle, and oxidative phosphorylation:

    • Glycolysis: Glucose → 2 pyruvate + 2 ATP + 2 NADH

    • Pyruvate Oxidation: 2 Pyruvate → 2 CO₂ + 2 Acetyl CoA + 2 NADH

    • Citric Acid Cycle: 2 Acetyl CoA → 4 CO₂ + 2 GTP + 6 NADH + 2 FADH₂

    • Oxidative Phosphorylation: 10 NADH + 2 FADH₂ → approximately 26-28 ATP

Photosynthesis Overview

  • Two main pathways involved:

    1. Light Reactions: Convert light energy into chemical energy (ATP and NADPH).

    2. Carbon Fixation Reactions: Use ATP and NADPH to produce carbohydrates.

Practice Questions Summary

  • Carbon dioxide is:

    • a) nonpolar; simple diffusion

    • b) polar; facilitated diffusion

  • During a typical hydrolysis reaction:

    • Energy required for bond breaking vs. energy released during product formation.

  • Enzyme Functionality:

    • Enzymes lower activation energy and regulate cell activity.

Conclusion

  • Understanding the properties and functions of biomolecules is core to cellular biology, driving processes such as signal transduction, energy metabolism, and the structural roles of proteins.