TLO week 1

Question 1

Identify cellular organelles and describe each of their functions (10)

Answer 1

1. Nucleus: controls cellular activities and houses genetic material
2. Mitochondria: Produces energy through ATP cellular resp (power house)
3. Enoplasmic Reticulum (ER)

Rough ER: Synthesizes proteins (ribbed with ribosomes)
Smooth ER: Synthesizes lipids, detox chemicals and stores calcium

4. Golgi Appartaus: Modifies, sorts and packages proteins and lipids for transport
5. Lysomes: Contains enzymes for digesting cellular waste and foreign materials
6. Ribosomes: synthesizes proteins by translating mRNA
7. Peroxisomes: Breaks down fatty acids and detox harmful substances
8. Cytoskeleton: provides structural support, facilitates cell movement and intracellular transport
9. Plasma membranes: Acts as a barrier
10. Centrosomes and centrioles: Organising microtubules during cell division

Question 2

Identify the 4 major macromolecules in human body and their sources

Answer 2

Proteins: From dietary amino acids

Lipids: From dietary fatty acids and glycerol

Carbohydrates: Dietary simple sugars

Nucleic Acids: Nucleotides synthesized in body or from diet

Question 3

Explain basis of fluid mosaic model of biological membranes and relate the structure to its function

Answer 3

Fluid mosaic model describes cell membranes as a phospholipid bilayer with embedded proteins

Phospholipids bilayer: Forms membrane structure

Fluidity: allows movement of membranes components

Embedded proteins: Performs various functions (transport, signaling etc)

Cholesterol: Regulates membrane fluidity and stability

Glycoproteins and glycolipids: Form glycocalyx for cell recognitions.

Question 4

Identify the four major macromolecules in the human body and their sources

Answer 4

1. Proteins: Sourced from dietary amino acids.
2. Lipids: Sourced from dietary fatty acids and glycerol.
3. Carbohydrates: Sourced from dietary simple sugars.
4. Nucleic Acids: Sourced from nucleotides synthesized in the body or from diet.

Question 5

Describe the major roles of proteins in the human body Proteins serve as

Answer 5

1. Structural components (e.g., collagen)
2. Enzymes catalyzing biochemical reactions
3. Transport molecules (e.g., hemoglobin)
4. Hormones (e.g., insulin)
5. Antibodies for immune function
6. Cell signaling receptors
7. Muscle contraction components (actin and myosin)

Question 6

Describe the major roles of lipids in the human body Lipids function as:

Answer 6

1. Energy storage (triglycerides)
2. Cell membrane components (phospholipids and cholesterol)
3. Insulation (subcutaneous fat)
4. Hormone precursors (steroid hormones)
5. Facilitators of fat-soluble vitamin absorption
6. Cell signaling molecules (lipid-based second messengers)

Question 7

Describe the major roles of carbohydrates in the human body Carbohydrates serve as:

Answer 7

1. Primary energy source (glucose)
2. Energy storage (glycogen)
3. Structural components (e.g., ribose in nucleic acids)
4. Cell recognition molecules (glycoproteins and glycolipids)
5. Dietary fiber for digestion and gut health

Question 8

Describe the major roles of nucleic acids in the human body Nucleic acids (DNA and RNA) are crucial for

Answer 8

1. Genetic information storage (DNA)
2. Protein synthesis (mRNA, tRNA, rRNA)
3. Gene regulation (miRNA and other regulatory RNAs)
4. Enzyme cofactors (e.g., NAD+ and FAD in metabolism)

Question 9

Discuss how dysfunction of macromolecules can result in disease Macromolecule dysfunction can lead to various diseases:

Answer 9

1. Proteins: Misfolding (e.g., Alzheimer’s) or enzyme deficiencies (e.g., Phenylketonuria)
2. Lipids: Cholesterol imbalance (atherosclerosis) or lipid storage disorders (e.g., Tay-
   Sachs)
3. Carbohydrates: Impaired glucose metabolism (diabetes) or glycogen storage diseases
4. Nucleic Acids: Genetic mutations (e.g., sickle cell anemia) or DNA repair defects
   (increased cancer risk)

Question 10

Identify cellular transport mechanisms used by a cell to move substances across the membrane and discuss factors that determine the type of transport used
Transport mechanisms:

Answer 10

1. Passive transport: Simple diffusion, facilitated diffusion, osmosis
2. Active transport: Primary active transport, secondary active transport
3. Vesicular transport: Endocytosis, exocytosis

Factors determining transport type:
* Concentration gradient
* Molecule size and polarity
* Membrane permeability
* Energy requirements
* Presence of specific transport proteins

Question 11

Explain the differences between passive and facilitated diffusion

Answer 11

Passive diffusion:
* Molecules move directly through the phospholipid bilayer
* No energy required
* Limited to small, nonpolar molecules

Facilitated diffusion:
* Requires transport proteins (channels or carriers)
* No energy required
* Allows passage of larger or polar molecules
* Can be regulated by the cell

Question 12

Explain the difference between primary and secondary active transport using relevant clinical examples

Answer 12

Primary active transport:
* Directly uses ATP for energy
* Example: Na+/K+ ATPase pump in neurons (maintains resting membrane potential)

Secondary active transport:
* Uses energy from electrochemical gradient created by primary active transport
* Example: Glucose-sodium cotransporter (SGLT) in kidney tubules (glucose reabsorption)

Question 13

Describe the stages of the cell cycle and the important functions that take place within each one

Answer 13

1. Interphase:

G1: Cell growth and preparation for DNA synthesis
S: DNA replication
G2: Preparation for mitosis

2. Mitotic phase:
   Mitosis: Nuclear division
   Cytokinesis: Cytoplasmic division
3. G0 phase: Quiescent or senescent state (optional)

Question 14

Explain the process of mitosis and describe the important events that take place in each phase

Answer 14

1. Prophase: Chromatin condenses, nuclear envelope breaks down, spindle fibers form
2. Metaphase: Chromosomes align at the metaphase plate
3. Anaphase: Sister chromatids separate and move to opposite poles
4. Telophase: Chromosomes decondense, nuclear envelopes reform, cytokinesis begins

Question 15

Identify the different types of stem cells in the human body and the structures they can potentially become (unipotent, pluripotent, multipotent and totipotent), and relate their function to therapeutic potential

Answer 15

Totipotent: Can form all cell types (e.g., zygote)

Pluripotent: Can form most cell types (e.g., embryonic stem cells)

Multipotent: Can form multiple cell types within a lineage (e.g., hematopoietic stem
cells)

Unipotent: Can form only one cell type (e.g., spermatogonial stem cells) Therapeutic potential: Regenerative medicine, tissue engineering, disease modeling, drug screening.

Question 16

Justify the importance of maintaining balance between cell division and apoptosis Balancing cell division and apoptosis is crucial for:

Answer 16

Tissue homeostasis
* Proper organ function
* Prevention of cancer and other diseases
* Embryonic development
* Immune system regulation

Question 17

Describe the process of meiosis Meiosis consists of two divisions:

Answer 17

Meiosis I: Homologous chromosomes pair, crossover, and separate

Meiosis II: Sister chromatids separate
Results in four haploid gametes with genetic diversity.

Question 18

Compare meiosis to mitosis

Answer 18

Similarities:
* Both involve DNA replication and cell division

Differences:
* Meiosis produces haploid gametes; mitosis produces identical diploid cells
* Meiosis involves two rounds of division; mitosis involves one
* Meiosis includes genetic recombination; mitosis does not
* Meiosis occurs only in germ cells; mitosis occurs in somatic cells

Question 19

Describe the major components that make up the human genome

Answer 19

1. Nuclear DNA: 23 pairs of chromosomes
2. Mitochondrial DNA: Circular DNA in mitochondria
3. Genes: Protein-coding sequences
4. Regulatory elements: Promoters, enhancers, silencers
5. Non-coding DNA: Introns, repetitive sequences
6. Telomeres: Protective end sequences of chromosomes

Question 20

Identify the major enzymes involved in DNA replication and their functions

Answer 20

1. DNA helicase: Unwinds the DNA double helix
2. DNA primase: Synthesizes RNA primers
3. DNA polymerase III: Main replicative enzyme, extends DNA strands
4. DNA polymerase I: Removes RNA primers, fills gaps
5. DNA ligase: Joins Okazaki fragments

Question 21

Compare and contrast the process of DNA replication in eukaryotic and prokaryotic cells

Answer 21

Similarities:
* Both use semiconservative replication
* Both require similar enzymes (helicases, polymerases, ligases)

Differences:
* Eukaryotic replication is slower and more complex
* Eukaryotes have multiple origins of replication; prokaryotes have one
* Eukaryotes replicate linear chromosomes; prokaryotes replicate circular DNA
* Eukaryotes have telomere maintenance; prokaryotes do not

Question 22

Explain the process of transcription and translation in a eukaryotic cell Transcription

Answer 22

1. Initiation: RNA polymerase binds to promoter
2. Elongation: RNA synthesis
3. Termination: RNA release
4. Post-transcriptional modifications: 5’ capping, 3’ polyadenylation, splicing

Translation:
1. Initiation: Ribosome assembly on mRNA
2. Elongation: Amino acid chain formation
3. Termination: Release of completed protein
4. Post-translational modifications: Folding, chemical modifications

Question 23

Define the term receptor and identify the different membrane proteins that can act as receptors

Answer 23

A receptor is a protein that binds to a specific signaling molecule, triggering a cellular response. Membrane proteins acting as receptors:

1. G protein-coupled receptors (GPCRs)
2. Receptor tyrosine kinases (RTKs)
3. Ion channel-linked receptors
4. Enzyme-linked receptors

Question 24

Identify and explain the roles of the major receptor types

Answer 24

1. G protein-coupled receptors (GPCRs): Signal transduction through G proteins
2. Receptor tyrosine kinases (RTKs): Phosphorylation of target proteins
3. Ion channel-linked receptors: Direct ion flow across membranes
4. Enzyme-linked receptors: Catalyze intracellular reactions

Question 25

Explain the role of proteins in cell signaling and communication Proteins play crucial roles in cell signaling:

Answer 25

1. Receptors: Detect and respond to signals 2. Signal transducers: Relay and amplify signals 3. Enzymes: Modify other proteins 4. Scaffold proteins: Organize signaling complexes 5. Transcription factors: Regulate gene expression 6. Ion channels: Control ion flow and membrane potential

Question 26

Distinguish between endocrine, paracrine and autocrine signaling mechanisms and the types of transduction pathways that can be activated

Answer 26

Endocrine signaling: Long-distance communication via bloodstream Paracrine signaling: Short-distance communication between nearby cells Autocrine signaling: Cell signals to itself. Transduction pathways: 1. cAMP pathway 2. Phosphoinositide pathway 3. JAK-STAT pathway 4. MAP kinase pathway Each signaling mechanism can activate various transduction pathways depending on the specific receptor and ligand involved.

Question 27

Explain the basic principles of enzyme function Enzymes are biological catalysts that:

Answer 27

1. Lower activation energy of reactions 2. Exhibit substrate specificity 3. Remain unchanged after catalysis 4. Function optimally under specific conditions (pH, temperature) 5. Can be regulated by various factors

Question 28

Describe the properties of enzyme kinetics

Answer 28

Key properties of enzyme kinetics include: 1. Michaelis-Menten kinetics 2. Km (Michaelis constant) and Vmax (maximum velocity) 3. Lineweaver-Burk plot for determining kinetic parameters 4. Effects of substrate concentration on reaction rate 5. Enzyme saturation

Question 29

Describe the different classifications of enzymes and their relative function Enzyme classifications

Answer 29

1. Oxidoreductases: Catalyze oxidation-reduction reactions 2. Transferases: Transfer functional groups between molecules 3. Hydrolases: Catalyze hydrolysis reactions 4. Lyases: Add or remove groups without hydrolysis 5. Isomerases: Catalyze intramolecular rearrangements 6. Ligases: Join two molecules using ATP hydrolysis

Question 30

Identify key enzyme inhibitors and their clinical relevance

Answer 30

1. Competitive inhibitors: Compete with substrate for active site (e.g., statins inhibiting HMG-CoA reductase) 2. Non-competitive inhibitors: Bind to allosteric site (e.g., aspirin inhibiting cyclooxygenase) 3. Irreversible inhibitors: Permanently modify enzyme (e.g., penicillin inhibiting bacterial cell wall synthesis) 4. Suicide inhibitors: Enzyme converts inhibitor to reactive form (e.g., acyclovir inhibiting viral DNA polymerase)

Question 31

Justify the use of glucose as the body's primary energy source

Answer 31

Glucose is the primary energy source because: 1. It's readily available from carbohydrate digestion 2. It can be quickly metabolized for energy 3. All cells can use it 4. It can be stored as glycogen for later use 5. It's essential for brain function

Question 32

Identify the locations of bioenergetic reactions in the cell

Answer 32

1. Cytoplasm: Glycolysis 2. Mitochondrial matrix: Krebs cycle, fatty acid oxidation 3. Inner mitochondrial membrane: Electron transport chain, oxidative phosphorylation 4. Endoplasmic reticulum: Lipid synthesis 5. Peroxisomes: Fatty acid oxidation (very long-chain fatty acids)

Question 33

Define aerobic and anaerobic metabolism and provide bioenergetic examples of each Aerobic metabolism

Answer 33

Requires oxygen for complete oxidation of substrates Example: Complete glucose oxidation through glycolysis, Krebs cycle, and electron transport chain. Anaerobic metabolism: Occurs without oxygen Example: Lactic acid fermentation during intense exerci

Question 34

Explain the major steps and products of glycolysis, Krebs cycle and the Electron Transport Chain (ECT)

Answer 34

Glycolysis: 1. Glucose → 2 Pyruvate 2. Net production: 2 ATP, 2 NADH Krebs cycle: 1. Acetyl-CoA → 2 CO2 2. Per cycle: 3 NADH, 1 FADH2, 1 GTP Electron Transport Chain: 1. NADH and FADH2

Question 35

Identify the key enzymes and steps in glycogen metabolism Key enzymes in glycogen metabolism

Answer 35

1. Glycogen synthase: Adds glucose units to glycogen 2. Glycogen phosphorylase: Breaks down glycogen to glucose-1-phosphate 3. Branching enzyme: Creates branch points in glycogen 4. Debranching enzyme: Removes branch points during glycogen breakdown Steps: 1. Glycogenesis: Glucose → Glucose-6-phosphate → Glucose-1-phosphate → UDP- glucose → Glycogen 2. Glycogenolysis: Glycogen → Glucose-1-phosphate → Glucose-6-phosphate → Glucose (in liver) or pyruvate (in muscle)

Question 36

Provide clinical examples of metabolism disorders

Answer 36

1. Diabetes mellitus: Impaired glucose metabolism 2. Phenylketonuria: Phenylalanine metabolism disorder 3. Glycogen storage diseases: Impaired glycogen metabolism 4. Fatty acid oxidation disorders: e.g., Medium-chain acyl-CoA dehydrogenase deficiency 5. Urea cycle disorders: e.g., Ornithine transcarbamylase deficiency

Question 37

Describe the sequence of reactions involved in the oxidation of fatty acids in the mitochondrion and its regulation

Answer 37

Fatty acid oxidation (β-oxidation): 1. Activation: Fatty acid → Fatty acyl-CoA 2. Transport into mitochondria via carnitine shuttle 3. β-oxidation cycle: a. Dehydrogenation (FAD → FADH2) b. Hydration c. Dehydrogenation (NAD+ → NADH) d. Thiolysis (CoA-SH) 4. Acetyl-CoA enters Krebs cycle Regulation: * Inhibited by high levels of acetyl-CoA and NADH * Stimulated by glucagon and epinephrine * Inhibited by insulin

Question 38

Describe the pathway for activation and transport of fatty acids to the mitochondrion for catabolism

Answer 38

1. Activation: Fatty acid + CoA + ATP → Fatty acyl-CoA + AMP + PPi 2. Carnitine shuttle: a. Fatty acyl-CoA + Carnitine → Fatty acyl-carnitine + CoA b. Transport across inner mitochondrial membrane c. Fatty acyl-carnitine + CoA → Fatty acyl-CoA + Carnitine 3. Fatty acyl-CoA enters β-oxidation cycle

Question 39

Explain the rationale for the pathway of ketogenesis and identify the major intermediates and products of this pathway

Answer 39

Rationale: Ketogenesis occurs when glucose is scarce and fatty acid oxidation is high, providing alternative fuel for the brain. Pathway: 1. Acetyl-CoA → Acetoacetyl-CoA 2. Acetoacetyl-CoA + Acetyl-CoA → HMG-CoA 3. HMG-CoA → Acetoacetate 4. Acetoacetate → β-hydroxybutyrate or Acetone Major intermediates: Acetoacetyl-CoA, HMG-CoA Major products: Acetoacetate, β-hydroxybutyrate, Acetone (ketone bodies)

Question 40

Describe the three mechanisms used by humans for removal of nitrogen from amino acids before the metabolism of their carbon skeleton

Answer 40

1. Transamination: Transfer of amino group to α-ketoglutarate, forming glutamate 2. Oxidative deamination: Removal of amino group as ammonia by glutamate dehydrogenase 3. Urea cycle: Conversion of ammonia to urea for excretion

Question 41

Outline the sequence of reactions in the urea cycle including key regulatory steps Urea cycle steps

Answer 41

1. Carbamoyl phosphate synthesis 2. Citrulline formation 3. Argininosuccinate synthesis 4. Argininosuccinate cleavage 5. Arginine cleavage to urea Key regulatory steps: * Carbamoyl phosphate synthetase I (rate-limiting) * N-acetylglutamate (allosteric activator)

Question 42

Define the terms and give examples of glucogenic and ketogenic amino acids Glucogenic amino acids

Answer 42

Can be converted to glucose Examples: Alanine, Aspartate, Glutamate Ketogenic amino acids: Can be converted to ketone bodies Examples: Leucine, Lysine Some amino acids are both glucogenic and ketogenic (e.g., Phenylalanine, Tyrosine)

Question 43

Summarise the sources and use of ammonia in animals, and explain the concept of nitrogen balance

Answer 43

Sources of ammonia: 1. Amino acid deamination 2. Bacterial action in the gut 3. Glutamine breakdown in the kidney Uses of ammonia: 1. Urea synthesis 2. Glutamine synthesis 3. Nucleotide synthesis Nitrogen balance: The state where nitrogen intake equals nitrogen excretion. Positive balance indicates growth or tissue repair, while negative balance suggests catabolism or inadequate protein intake.

Question 44

Identify the essential amino acids and the metabolic sources of the nonessential amino acids

Answer 44

Essential amino acids (cannot be synthesized by humans): Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, V aline Nonessential amino acids (can be synthesized): Alanine, Arginine, Asparagine, Aspartate, Cysteine, Glutamate, Glutamine, Glycine, Proline, Serine, Tyrosine Metabolic sources of nonessential amino acids: 1. Transamination of keto acids 2. Conversion from other amino acids 3. Synthesis from metabolic intermediates (e.g., 3-phosphoglycerate for serine)

Question 45

Cells placed in an isotonic solution will?

Answer 45

Remain the same size

Question 46

Enzymes work by?

Answer 46

Decreasing the activation energy

Question 47

Base pairing events, which formation is the strongest bond

Answer 47

Cytosine bound to Guanine

Question 48

Are lipids hydrophobic and phosphates hydrophilic?

Answer 48

Yes

Question 49

Which organelle is essential for cells to replicate?

Answer 49

Nucleus

Question 50

Homoeostasis can be described as?

Answer 50

The maintenance of a relatively stable internal environment

Question 51

Protein coding region of a gene begins with?

Answer 51

The first AUG or start codon encountered by the ribosome

Question 52

Form of cell death involving pyknosis, chromatin condensation and fragmentation as well as engulfment by resident phagocytes

Answer 52

Apoptosis

Question 53

How many chromosomes are found in the human oocyte

Answer 53

23

Question 54

For fatty acids synthesis to occur

Answer 54

Pyruvate dehydrogenase must be inactivated

Question 55

The demand for nucleotide biosynthesis is high during which stage in the cell cycle?

Answer 55

S- phase

Question 56

The enzyme responsible for the synthesis of mRNA during the transcription

Answer 56

RNA Polymerase

Question 57

Proteins are made up of

Answer 57

Amino acids