Carbohydrate Metabolism Quiz

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Questions and Answers

What role does the debranching enzyme serve in carbohydrate metabolism?

It removes glucose units from the branch to create a linear chain. (correct)

It oxidizes glucose to produce energy.

It phosphorylates glucose-1-phosphate to glucose-6-phosphate.

It synthesizes glucose from fatty acids.

Which activity is NOT performed by the debranching enzyme?

Conducting phosphotransfer between glucose residues. (correct)

Removing glucose residues to create a branch.

Transferring glucose residues to another branch.

Catalyzing the hydrolysis of the a-1,6-linkage.

Gluconeogenesis primarily uses which of the following as substrates?

Glucose and fatty acids.

Glucogenic amino acids and lactate. (correct)

Fructose and sucrose.

Glycogen and glycyl residues.

Which enzyme is responsible for converting glucose-1-phosphate to glucose-6-phosphate?

Phosphoglucomutase. Signup and view all the answers

What is the primary purpose of the cori cycle in energy metabolism?

To recycle lactate back to glucose. Signup and view all the answers

What is the primary consequence of hereditary fructose intolerance (HFI) in patients?

Accumulation of fructose-1-phosphate Signup and view all the answers

What role does fructokinase play in the digestion of fructose?

Rapidly phosphorylates fructose to form fructose-1-phosphate Signup and view all the answers

Which enzyme's absence is primarily responsible for the symptoms of hereditary fructose intolerance?

Aldolase B Signup and view all the answers

What is the resulting metabolic pathway after fructose is converted to fructose-1-phosphate?

Glycolysis Signup and view all the answers

How does the lack of feedback inhibition in fructokinase affect fructose metabolism?

Leads to excessive phosphorylation of fructose Signup and view all the answers

What is a characteristic feature of hyaluronans?

They are the largest polysaccharides produced by vertebrate cells. Signup and view all the answers

Which of the following is NOT a function of dermatin sulfate?

Promoting muscle growth Signup and view all the answers

Chondroitin-4-sulfate is primarily associated with which of the following components?

Proteins to form proteoglycans Signup and view all the answers

What type of complexes do hyaluronans form in the extracellular matrix?

Non-covalently formed complexes with proteoglycans Signup and view all the answers

The molecular weight range of hyaluronans is between which values?

$100,000 - 10,000,000$ Signup and view all the answers

What type of glycosaminoglycan is involved in forming proteoglycans that bind to growth factors?

Heparan sulfate Signup and view all the answers

Which of the following factors is NOT associated with heparan sulfate proteoglycan (HSPG)?

Creatine kinase Signup and view all the answers

Which statement accurately describes keratan sulfate in relation to proteoglycans?

It can associate with proteins to form proteoglycans. Signup and view all the answers

Which of the following best describes the role of heparan sulfate proteoglycans?

They facilitate the binding of various growth factors. Signup and view all the answers

What is the primary function of fibroblast growth factors (FGFs) bound by heparan sulfate proteoglycans?

They enhance cellular communication and proliferation. Signup and view all the answers

What is the primary role of NAD+ in the reaction involving ethanol and alcohol dehydrogenase (ADH)?

To serve as a coenzyme that is not consumed Signup and view all the answers

Which compound is produced alongside NADH during the conversion of ethanol by ADH?

Acetaldehyde Signup and view all the answers

What happens to NADH after its formation in the reaction of ethanol with ADH?

It is oxidized back to NAD+ in a different reaction Signup and view all the answers

How does ALDH function in the metabolic pathway related to alcohol consumption?

It oxidizes acetaldehyde into acetic acid Signup and view all the answers

In the context of enzyme kinetics, what effect does a competitive inhibitor have on Km?

It increases Km Signup and view all the answers

Which of the following statements is true regarding the transition state in an enzymatic reaction?

The transition state is less stable than the substrate and product Signup and view all the answers

What characterizes uncompetitive inhibition in enzyme kinetics?

Both Vmax and Km decrease Signup and view all the answers

In the summary table of enzyme activity, what does a higher Km value in the presence of a competitive inhibitor indicate?

Decreased affinity of the enzyme for the substrate Signup and view all the answers

Which type of inhibitor results in a decrease of Vmax while Km remains constant?

Pure noncompetitive inhibitor Signup and view all the answers

What is the primary role of 2,3-bisphosphoglycerate (2,3-BPG) in red blood cells?

To stabilize the T-state (deoxy) form of hemoglobin Signup and view all the answers

Why does fetal hemoglobin (HbF) exhibit a higher affinity for oxygen compared to adult hemoglobin (HbA)?

It has a serine instead of histidine, reducing positive charges Signup and view all the answers

How does high altitude affect the production of 2,3-BPG and oxygen unloading?

Increases 2,3-BPG production and enhances oxygen unloading Signup and view all the answers

What mutation is responsible for sickle-cell anemia?

Substitution of Valine for Glutamic acid in hemoglobin beta chains Signup and view all the answers

What occurs during the conversion of sickle hemoglobin (HbS) from the oxy to deoxy form?

Formation of a hydrophobic pocket leading to cell aggregation Signup and view all the answers

In the absence of 2,3-BPG, what is the expected effect on oxygen binding to hemoglobin?

Oxygen binding becomes hyperbolic and less cooperative Signup and view all the answers

Which process occurs exclusively in the mitochondria and requires oxygen?

Citric acid cycle Signup and view all the answers

What is the primary purpose of glycolysis?

To break down glucose into pyruvate while generating ATP Signup and view all the answers

How does the structure of fetal hemoglobin (HbF) differ from that of adult hemoglobin (HbA) in terms of charge?

HbF has fewer positive charges due to amino acid substitutions Signup and view all the answers

Study Notes

Lecture 1 - Cell and Water

Learn the structure and function of organelles in the cell
Learn the four macromolecules
Solutes, solvents, solutions
- Types of solutes
  - Ionic
    - Hydrophilic
  - Polar
    - Hydrophilic
    - Forms hydrogen bonds with water
  - Non-polar
    - Hydrophobic
    - Attracted to each other in water
- Types of bonds
  - Covalent > ionic > hydrogen > van der Waals
  - Hydrogen bonds are weak bonds that can break easily.
  - Protons cannot exist in aqueous solution due to their positive charge. (H3O+)
Water
- Covalent > ionic > hydrogen > van der Waals
- Can form hydrogen bonds (weak bonds that can break easily)
- Protons cannot exist in aqueous solution due to their positive charge (H3O+)

Lecture 2 - pH

pH - logarithmic measure of H+ concentration in a solution
pH = -log [H+]
Low pH = more H+
High pH = less H+
Many biochemical reactions only occur at specific pH levels.
[H+] can vary greatly, and it would be more straightforward to communicate in pH than [H+].
pH measurement:
- probe
- litmus paper
- [H+] in water
- 10^-7 M in water (pH = 7)
- water is in equilibrium (pOH of water is also 7)
- pOH + pH =14
- decrease in pH by 1 unit → 10x increase in [H+]
- strong acids dissociate completely into ions
- weak acids dissociate partially
- acid increases [H+] and decreases pH
- base decreases [H+] and increases pH
- water autoionization
- acts as both acid and base
- acid → conjugate base (nomenclature: -ate)
- base → conjugate acid (nomenclature: -ic)
- Bronsted -Lowry definition
- Ka tells you the acid strength
 - increasing Ka → increasing acid strength ← decreasing pKa
 - Ka <10^-3 = weak acid
 - 10^-3 < Ka < 1 = moderate acid
 - Ka > 1 = strong acid
 - Henderson-Hasselback equation ○ pH = pKa + log [base] / [acid]

Lecture 3 - Amino Acids

Amino acids are major constituents for brains, nerve, muscle, blood, skin, and internal organs.
3 ways to identify/ name amino acids:
- 1 letter abbreviation
- Data bases of sequences will be easier to be recorded and takes less space
- Bioinformatics mainly uses the 1 letter abbreviation
20 amino acids
9 essential amino acids
11 non-essential amino acids
- Alanine, Arginine, Aspartic Acid, Asparagine, Cysteine, Cystine, Glutamic Acid, Glutamine, Glycine, Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Proline, Threonine, Tryptophan, Tyrosine, Valine

Lecture 4 - Proteins

SARS CoV 2 binds to receptors on lung cells
Central dogma of biology = DNA → RNA → protein
Protein is a linear polymer of amino acids.
First amino acid is methionine, but often removed after translation.
Condensation/ dehydration reaction to form the peptide bond
Amino terminus (N terminus), carboxy terminus (C terminus)
Constant backbone, Variable side chains
Peptide (shorter) vs protein/ polypeptide (longer, >50 a.a.)
Dipeptide (2), tripeptide (3), oligopeptide (12-20)
Molecular weight of a protein is expressed in daltons.
Mean molecular weight of an amino acid residue ~ 110 dalton.
SDS-PAGE = a technique for separating mixtures of different sizes
Isoelectric point (pI) = pH at which the molecule carries no net charge.
pH < pl, then protein charge +
pH > pl, then protein charge -
Applications of proteins:
- Diagnostics

Lecture 5 - Forms and Functions of Enzymes

Enzyme = protein catalyst that increases the rate of a reaction
Not consumed in reaction
Exception: ribozyme - RNA acts like an enzyme
Active site has 3D conformation (usually forming a cleft)
Binding via weak forces; quick binding and unbinding
Major classes of enzymes:
- Oxidoreductase (redox)
- Transferases (transfer of functional groups)
- Hydrolases (hydrolysis)
- Lyases (group elimination to form double bonds)
- Isomerases (isomerisation)
- Ligases (bond formation coupled with ATP hydrolysis)
Features of enzymes:
- Higher reaction rates
- Milder reaction conditions (compared to chemical catalysts)
- Capacity for regulation
- Greater reaction specificity
- Active site provides unique combination of specificity determined by the 3D structure
  - inorganic metal ions (e.g., Mg2+ )
  - coenzymes (organic molecules)

Lecture 6 - Enzyme Kinetics & Enzyme Inhibition

Rate-determining step = step with highest activation energy
Intermediate = stable chemical structure that can be isolated
Kinetics = rate of change of reactants and products
Rate law: rate = k [A] (first order), rate = k [A]m [B]n (second order)
Determining velocity-substrate curve by experimentation
- Decreasing rate of reaction as time passes → decrease in reactant concentration
Chemical rxn vs Enzyme-catalysed reaction
Chemical rxn: linear plot of rate against [S]
Enzyme: hyperbolic curve of rate against [S]
Michaelis-Menten Equation:

V0 = Vmax[S] ____ Km + [S]

Lineweaver-Burk Plot (Double-Reciprocal Plot)
Michaelis constant Km = (k-1 + k2)/k1
Enzyme with smaller Km can achieve max velocity at lower substrate concentrations
Enzyme inhibitors:
- Irreversible Inhibition
  - forms covalent bonds at active site of enzyme
  - decreases Vmax
- Reversible Inhibition
  - competes with the substrate
  - uncompetitive

Lecture 7 - Enzyme Regulation

Control of enzyme synthesis amounts
Control of enzyme activity
- Subcellular localisation
  - Hexokinase
  - Glucokinase
  - present in different tissues and exhibit different regulatory properties
    - I, II, III: present in most tissues except liver; broad substrate specificity
    - IV (aka Glucokinase): predominates in liver (where glucose concentrations are higher).
Metabolic regulation
Glucokinase: lower Km than hexokinase, is activated by elevated glucose levels to meet higher energy needs.
Inhibited by high levels of glucose-6-phosphate.
Hexokinase: inhibited by its product, glucose-6-phosphate (feedback inhibition), is more prevalent in cells that need less glucose.

Lecture 8 - Cellular Oxygenation

Myoglobin is needed to prevent Fe2+ from oxidizing to Fe3+ and to prevent the release of superoxide.
Hyperbolic oxygen dissociation curve
Haemoglobin has 4 heme groups, so it can bind to four O2 in total.
They bind one by one resulting in a conformational change in adjacent subunits.
Effectors that affect oxygen binding:
- Protons
Increasing acidity leads to decreased affinity for O2 (Bohr effect)
- CO2
Produces carbamate, stabilizing the T-state and promoting O2 release.
- 2,3-BPG (a metabolite)
stabilizes the T state, reducing oxygen affinity and favoring oxygen release from haemoglobin in tissues.

Lecture 9 - Carbohydrate Metabolism

• Glycolysis breaks down glucose (6C) into pyruvate (3C). • ATP is produced but some ATP is needed in the process. • NADH produced is also used as an electron carrier. • Glycolysis occurs in the cytoplasm and does not require oxygen • When oxygen is present pyruvate enters the mitochondri — first, it reacts with enzyme A to form acetyl CoA, which enters the Krebs cycle or TCA cycle. • A lot of NADH is generated in the conversion of pyruvate to acetyl-CoA. • Electron transport chain: transmembrane proteins transfer electrons from NADH to these protein complexes, releasing energy that is used to form ATP - NADH transfers to protein complexes that are in the mitochondrial matrix, high energy electron carriers. • Overall: 1 glucose → 2 pyruvate + 2 ATP • 2x (pyruvate → acetyl CoA + NADH) • TCA cycle (for 2 pyruvate/ 1 glucose): 6 NADH + 2 FADH2 + 2 ATP • Total: 10 NADH, 2 FADH2, 4 АТР → 30ATP + 4 ATP + 4ATP = 38 ATP (36 if using glycerol-phosphate shuttle, because 2 NADH is converted to 2FADH2, which each produce 1 ATP)

Lecture 10 - Carbohydrates as Cellular Components

Carbohydrates are composed of C, H, and O.
Classified into aldoses and ketoses based on carbonyl group:
- Aldose = aldehyde
- Ketose = ketone
Monosaccharides are named based on the number of carbons.
Monosaccharides can exist as cyclic structures (in solution).
Stereoisomers of monosaccharides (differ in arrangement around asymmetric carbons) are possible (L- forms and D-forms).
Epimers differ in the configuration at one carbon.
Cyclisation of monosaccharides
- Forms ring structures—either pyranose (6-membered) or furanose (5-membered)
- The carbon bonded to the carbonyl group becomes the anomeric carbon. - Anomers are possible because of this new chiral carbon.

Lecture 11 - Lipid and Cellular Membrane

Fatty acids are long hydrocarbon chains with a carboxylic acid group at the end.
- Saturated fatty acids have no double bonds, and tend to exist as solids. They have higher melting points.
- Unsaturated fatty acids have double bonds, and tend to exist as liquids. They have lower melting points. and tend to be more fluidic.
Triacylglycerols (also called triglycerides)
Glycerol has 3 -OH groups.
Esterification between carboxylic acid and glycerol to form Triglycerides
- Simple triglyceride has all fatty acids the same
- Mixed triglyceride has different fatty acids.
Glycerophospholipids
Phosphatidate
Third -OH Group is reacted with phosphate
Major Phospholipid Structures
Phosphatidylcholine (POPC)
Phosphatidylglycerol (POPG)
Phosphatidylethanolamine (POPE)
Phosphatidylserine (POPS)
Sphingolipids (derivatives of sphingosine)
Sphingomyelin: ceramide + phosphocholine or phosphoethanolamine groups
Cerebrosides: ceramide + single sugar (glucose or galactose)
Gangliosides: ceramide + oligosaccharides
Cholesterol is a major component of animal cell membranes.
Cholesterol amphipathic molecule with both a hydrophilic and a hydrophobic region. that allows cholesterol to insert themselves in lipid bilayer

Lecture 12 - Nucleic Acid Structure and Function

Nucleic acids are polymers made of nucleotides.
Nucleotides consist of a nitrogenous base, a pentose sugar (ribose or deoxyribose), and a phosphate group.
Nitrogenous bases are classified as purines (Adenine, Guanine) and pyrimidines (Cytosine, Thymine, Uracil).
Nucleotides are linked together by phosphodiester bonds
Phosphodiester bonds form a sugar-phosphate backbone — the backbone is directional (5´ → 3´).
DNA Structure
DNA is a double helix with two antiparallel strands
The bases pair with each other—A pairs with T (by 2 H bonds) and G pairs with C (by 3 H bonds)
DNA can exists in B-form, A-form, Z-form.
B-form: most common form in cells
A-form: dehydrated or dsRNA
Z-Form: left hand helical structure, mostly involves in gene expression.
RNA Structure
mRNA, tNA, rRNA, miRNA, siRNA
coding/non-coding RNA.

Lecture 13 - Integration of Biomolecules in Cellular Function

Blood glucose homeostasis
- incretin hormones: (short chains of amino acids), are secreted in response to increase in glucose level to signal the pancreas to release insulin. (e.g. GLP-1, GIP)
- insulin: a protein hormone synthesized in beta cells of pancreas that suppresses glycogenolysis and promotes glycogen synthesis and increase glucose transport into cells.
- Glucagon: a peptide hormone secreted by alpha cells of the pancreas that stimulates glycogenolysis and gluconeogenesis to increase blood glucose levels.
Type I Diabetes (insulin-dependent): autoimmune destruction of beta cells
Type II Diabetes (non-insulin-dependent): results from insulin resistance - Treatment strategies
GLP-1 receptor agonists → increase lifetime of insulin in the bloodstream, preventing glucose level from increasing too quickly after eating.
DPP4 Inhibitors prevent breakdown of GLP-1 so it has a longer effect on the body.
SGLT2 inhibitors → preventing the kidney from reabsorbing some of the glucose in the blood.

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Test your knowledge on carbohydrate metabolism, focusing on key enzymes and metabolic pathways. This quiz covers topics such as the role of debranching enzymes, gluconeogenesis, and the Cori cycle. Perfect for students studying biochemistry or related fields.