Unit 4: Carbon, Energy Flow, and Metabolism - Key Concepts and Processes

What is the first of the three main questions investigated in Unit 4 regarding carbon and energy flow?

What are the structures of the molecules we eat and how does that influence their movement in our bodies?

What is the second of the three main questions investigated in Unit 4 regarding carbon and energy flow?

How do hormones and feedback loops regulate our use of carbon and energy?

What is the third of the three main questions investigated in Unit 4 regarding carbon and energy flow?

How are different molecules in our diet metabolized as sources of carbon and energy?

Can lipids freely diffuse into cells?

Yes

Can glucose freely diffuse into cells?

No (it requires a transporter)

In signal transduction, do the actual molecules (like insulin) flow across the cell membrane?

No (only information/signal flows)

What are two advantages of signal transduction over simple transport?

1. It enables information flow without molecule flow. 2. It can amplify a signal leading to multiple downstream effects.

Does glucose transport involve the flow of information, molecules, or both?

Both

What organ is triggered to release insulin when blood glucose is high?

The pancreas

As blood glucose levels drop, what happens to insulin levels?

They drop

Which two tissues use glucose the most in the human body?

1. The brain 2. Muscles

What is excess glucose stored as in adipocytes?

Fat

What is excess glucose polymerized into for storage in liver cells?

Glycogen

What hormone does the pancreas release when blood glucose is low?

Glucagon

What is the effect of glucagon binding to receptors on liver cells?

It triggers a signaling cascade to break down glycogen and release glucose into the bloodstream.

What happens to glucagon levels as blood glucose levels increase?

They drop

What type of feedback loop is used to maintain blood glucose homeostasis?

Negative feedback loop

How is Type 1 Diabetes defined?

An inability to produce insulin.

How is Type 2 Diabetes defined?

An inability to respond to insulin (insulin resistance).

What is the primary cause of the 'turning down' of insulin receptor signaling in Type 2 Diabetes?

Chronic high blood glucose (typically from overeating) leads to sustained high insulin levels.

What are three ways medications can treat Type 2 Diabetes?

1. Improve insulin responsiveness 2. Increase insulin production 3. Increase glucose secretion in urine

What is the HbA1c percentage threshold for a diagnosis of Diabetes?

≥ 6.5%

What is the Fasting Plasma Glucose threshold for a diagnosis of Diabetes?

≥ 126 mg/dL

What is the Oral Glucose Tolerance Test threshold for a diagnosis of Diabetes?

≥ 200 mg/dL

What is the HbA1c percentage range for 'Prediabetes'?

5.7 - 6.4%

What are the two general types of breakdown involved in digesting a meal?

1. Mechanical breakdown 2. Chemical breakdown

Which enzyme in the esophagus and pancreas splits starch into maltose?

Amylase

What chemical breakdown occurs in the stomach?

Proteases (protein → polypeptides) and stomach acids.

What is the function of bile salts released by the liver/gallbladder?

Emulsification of lipids.

What do Lipase enzymes do in the pancreas?

Convert triglycerides into fatty acids.

What do Endopeptidase enzymes do in the pancreas?

Convert peptides into amino acids.

What are enzymes (mostly)?

Proteins

What is the 'Transition State' in enzymatic catalysis?

The position where molecules (substrates) are held together to make it easier to form a product.

How does the 'Induced Fit Model' differ from the 'Lock and Key Model'?

Enzyme-substrate binding creates a new shape that makes it easier for the product to form (it is not a static exact fit).

On a reaction progress curve, what does the X-axis represent?

Reaction progress from start (left) to end (right).

On a reaction progress curve, what does the Y-axis represent?

Gibbs Free Energy

What does a positive change in free energy (ΔG) indicate about a reaction?

Energy is required (non-spontaneous).

What does a negative change in free energy (ΔG) indicate about a reaction?

Energy is released (spontaneous).

How do enzymes make a reaction 'easier' to occur on a reaction progress curve?

They lower the activation energy.

Is glucose polar or non-polar?

Polar

What property of glucose makes it unable to freely diffuse across the cell membrane?

It is polar (and the membrane interior is non-polar).

What property of lipids allows them to diffuse through cell membranes?

They are non-polar.

What is a 'Kinase'?

An enzyme that catalyzes the addition of a phosphate group (phosphorylation).

What is the effect of phosphorylating glucose once it enters a cell?

It adds a bulky negative charge, trapping the glucose in the cell.

What is an amino acid 'symporter'?

A transporter that moves two molecules (e.g., AA and Na+) in the same direction across the membrane.

What provides the potential energy to drive the transport of certain amino acids into cells?

The flow of Na+ down its concentration gradient.

Why is it 'easier' to move a nucleoside across a membrane than a nucleotide?

Nucleosides lack the highly charged phosphate group found in nucleotides.

Which class of hormones (Protein, Amine, or Lipid) is the largest in size?

Protein/Peptide hormones

Can protein or peptide hormones freely diffuse across cell membranes?

No

Where are hormone receptors usually located?

Within the cell membrane.

What are the four main stages of cellular respiration?

1. Glycolysis 2. Pyruvate Processing 3. Citric Acid Cycle 4. Electron Transport Chain/ATP Synthesis

Where in the cell does Glycolysis occur?

The cytoplasm

Where in the cell does Pyruvate Processing occur?

The mitochondrial matrix

Where in the cell does the Citric Acid Cycle occur?

The mitochondrial matrix

What is the final product of Glycolysis?

Pyruvate

How many carbons are in one molecule of Pyruvate?

3

How many molecules of Acetyl CoA are generated from one glucose molecule?

2

What is the first step of the Citric Acid Cycle?

Two carbons (from Acetyl CoA) are added to oxaloacetate.

In the Citric Acid Cycle, what form do the carbons take when they exit?

CO2

What is the general pattern of carbon oxidation in the Citric Acid Cycle?

Carbon is oxidized every time it forms a new covalent bond to a more electronegative atom (like Oxygen).

What is the final electron acceptor in the Electron Transport Chain (ETC)?

Oxygen (O2)

Which molecule donates its electrons to the ETC at Complex I?

NADH

Which molecule donates its electrons to the ETC at Complex II?

FADH2

Is H+ pumped at Complex II of the ETC?

No

Where is the concentration of H+ increasing during electron transport?

The intermembrane space

How does ATP synthase generate ATP?

It uses the flow of H+ down its concentration gradient (from intermembrane space to matrix).

Which leads to the generation of more ATP: NADH or FADH2?

NADH (because it enters at Complex I and contributes to more H+ pumping).

What is 'Fermentation'?

Anaerobic respiration that occurs when there is not enough O2 for the ETC to function.

What is the primary purpose of Fermentation?

To regenerate NAD+ from NADH so that Glycolysis can continue.

What is Pyruvate converted to during human fermentation?

Lactate (lactic acid)

What happens to blood glucose levels when Leptin decreases insulin synthesis/secretion?

They increase

What happens to blood glucose levels when Leptin increases insulin receptor sensitivity?

They decrease

What happens to blood glucose levels when Ghrelin increases glucagon secretion?

They increase

What happens to blood glucose levels when Ghrelin decreases insulin receptor sensitivity?

They increase

What are the four components of the 'Resource Access Index' that correlate with diabetes prevalence in the US?

1. Education, 2. Employment, 3. Financial resources, 4. Sufficient housing

In which geographic region of the United States is diabetes prevalence the highest?

The Southeast

What does the 'Secondary structure' (2°) of a protein represent?

The 'backbone' of the protein (local folding into helices or sheets).

What does the 'Tertiary structure' (3°) of a protein represent?

The three-dimensional folding pattern due to side chain interactions (the space the protein takes up).

What does the 'Quaternary structure' (4°) of a protein represent?

A protein consisting of more than one amino acid chain.

Is the amino acid Alanine's R-group (-CH3) polar or non-polar?

Non-polar

Is the amino acid Glutamine's R-group polar or non-polar?

Polar

In the electronegativity ranking O > N > C ≈ P ≈ H, which atom is the most electronegative?

Oxygen (O)

Why are lipids transported in chylomicrons instead of as free lipids in the bloodstream?

Lipids are non-polar and cannot dissolve in the polar environment of the bloodstream.

What components make up a chylomicron?

Several kinds of lipids (triglycerides, cholesterol, phospholipids) and a little bit of protein.

How are phospholipids arranged on the outside of a chylomicron?

The polar hydrophilic heads face the outside (bloodstream) and the non-polar hydrophobic tails face the inside.

Which class of hormones includes Testosterone and Estrogen?

Lipid hormones (steroids)

Which class of hormones includes Epinephrine (Adrenaline) and Melatonin?

Amine hormones

What happens to hormones that are not interacting with a receptor?

They eventually break down (the signal goes away).

What are the two parts/subunits of the insulin receptor?

Alpha (α) and Beta (β)

In Step 3 of the Citric Acid Cycle, what molecule is produced when isocitrate is oxidized?

α-Ketoglutarate

In Step 3 of the Citric Acid Cycle, what two byproducts are released?

NADH and CO2

In Step 4 of the Citric Acid Cycle, what molecule is produced when α-Ketoglutarate is oxidized?

Succinyl CoA

How many carbons exit the Citric Acid Cycle per one turn (one Acetyl CoA)?

2 carbons (as CO2)

How many carbons enter the Citric Acid Cycle per one turn (one Acetyl CoA)?

2 carbons

What specific electron carrier is produced during Step 6 of the Citric Acid Cycle?

FADH2

When people lose weight, what is the physical form of the mass that is lost?

CO2 (exhaled during respiration)

In the 'Weasel vs Sloth vs Polar Bear' plot, what is represented on the X-axis?

Ambient temperature (Ta) in °C

In the 'Weasel vs Sloth vs Polar Bear' plot, what is represented on the Y-axis?

Metabolic rate (arbitrary units)

Based on the mouse metabolic data, what is the mouse's 'thermoneutral zone' (where metabolic level is lowest)?

Approximately 27-37°C (80-98°F)

In the vulture study (Moreno-Opo et al., 2020), what does the term 'aggressor' signify?

A species that can outcompete another in competitive interactions.