Topic 2: Cellular Biology- Structure Metabolism

What are the three main tenets of cell theory?

1. All living organisms are made of one or more cells.

2. The cell is the basic unit of structure and function in living organisms.

3. All cells come from pre-existing cells.

Easy memory: All life = cells → Cells = basic unit → Cells come from cells.

What are the three basic parts of a human cell?

• Plasma (cell) membrane

• Cytoplasm

• Nucleus

What does the plasma membrane do?

Forms the cell’s outer boundary and controls what enters and leaves the cell.

What does the cytoplasm do?

Contains the cytosol and organelles and is the site of many cellular chemical reactions.

What does the nucleus do?

Stores DNA and directs cell activities by controlling gene expression (instructions).

Why is the cell considered the basic structural and functional unit of life?

The cell is the smallest unit of life that can perform all essential life functions.

What is the difference between cytoplasm and cytosol?

Cytoplasm = cytosol + organelles.
Cytosol = the fluid portion of the cytoplasm.

Easy memory: Cytoplasm = fluid + organelles; Cytosol = fluid only.

How does a cell’s surface-area-to-volume ratio limit its size and ability to exchange materials?

As a cell gets larger, its volume increases faster than its surface area, making it harder to exchange nutrients and wastes efficiently. This limits cell size.

Easy memory: Bigger cell → lower SA:V ratio → less efficient exchange.

What are the major organelles of a cell?

• Nucleus

• Mitochondria

• Ribosomes

• Rough ER

• Smooth ER

• Golgi apparatus

• Lysosomes

• Cytoskeleton

State one primary function of the nucleus…

Stores DNA

State one primary function of the mitochondria…

Produce ATP (energy)

State one primary function of the ribosomes…

Makes proteins.

State one primary function of the rough ER…

Processes proteins.

State one primary function of the smooth ER…

Makes lipids.

State one primary function of the golgi apparatus…

Modifies and packages proteins.

State one primary function of the lysosomes…

Digests and recycles materials.

State one primary function of the cytoskeleton…

Provides structure and helps with cell movement.

What is the difference between membranous and non-membranous organelles?

• Membranous organelles → surrounded by a membrane (e.g., nucleus, mitochondria, ER, Golgi, lysosomes).

• Non-membranous organelles → not surrounded by a membrane (e.g., ribosomes, cytoskeleton).

How does an organelle’s structure support its function?

An organelle’s structure is specialized to help it perform its function. For example, mitochondrial cristae increase surface area, allowing more ATP-producing reactions to occur.

Easy memory: Structure → supports function.

How does organelle abundance relate to cell type?

Cells have more of the organelles they need for their specific functions. For example, muscle cells have many mitochondria for ATP, while secretory cells have extensive rough ER for protein production.

Easy memory: More work → more of the organelle needed.

What are the roles of the cytoskeleton in support, intracellular transport, and movement?

The cytoskeleton:

• Supports the cell and maintains its shape.

• Transports materials within the cell.

• Enables movement of the cell or cell parts.

Easy memory: Support → Transport → Movement.

What is the path of a secreted protein through a cell?

Ribosome → Rough ER → Golgi apparatus → Vesicle → Plasma membrane → Outside the cell

Easy memory: Make → Process → Package → Transport → Secrete.

What organelles make up the endomembrane system?

Rough ER, Golgi apparatus, vesicles, lysosomes, and plasma membrane.

What is the role of vesicles in moving material between organelles?

Vesicles are small membrane-bound sacs that transport proteins and other materials between organelles and to/from the plasma membrane.

Easy memory: Vesicles = cellular delivery trucks.

What happens to a protein in the ER and Golgi?

• Rough ER: Protein is folded and begins modification.

• Golgi: Protein is further modified, tagged, and packaged for delivery.

How does exocytosis complete secretion at the plasma membrane?

A vesicle fuses with the plasma membrane, releasing its contents outside the cell.

What is the role of lysosomes in breaking down worn organelles and ingested material?

Lysosomes contain digestive enzymes that break down worn-out organelles and ingested materials, allowing the cell to recycle useful components.

Describe the parts of the nucleus…

• Nuclear envelope: Double membrane surrounding and protecting the nucleus.

• Nuclear pores: Openings that control what enters and leaves the nucleus.

• Nucleolus: Produces ribosomes.

• Chromatin: DNA + proteins that contain the cell’s genetic information.

What is the nucleus’s role as the cell’s control center?

The nucleus stores the cell’s DNA, which contains the instructions for making proteins and carrying out cell functions. It acts as a control center by regulating gene expression and directing cell activities.

What is the nucleus’s role as the cell’s control center?

The nucleus stores the cell’s DNA, which contains the instructions for making proteins and carrying out cell functions. It acts as a control center by regulating gene expression and directing cell activities.

What does the nucleolus do?

The nucleolus assembles ribosome subunits, which are later used to make proteins.

What is the difference between chromatin and chromosomes?

• Chromatin: Loose, uncoiled DNA + proteins found in the nucleus, especially when the cell is not dividing.

• Chromosomes: Tightly coiled and condensed chromatin that becomes visible during cell division.

How do nuclear pores regulate movement into and out of the nucleus?

Nuclear pores are openings in the nuclear envelope that control what enters and leaves the nucleus. Small molecules can pass through more easily, while larger molecules require specific transport proteins.

How are DNA, genes, and proteins related?

DNA contains the cell’s genetic information. Genes are specific sections of DNA that contain instructions for making proteins. Proteins then perform many of the cell’s functions.

What does DNA do?

DNA stores the instructions for making the body’s proteins, which carry out many important functions in cells.

What are transcription and translation?

• Transcription: The process of copying DNA into mRNA.

• Translation: The process of using mRNA to build a protein.

Where does transcription occur?

In the nucleus: DNA → mRNA

• Nucleus = transcription

Where does translation occur?

At ribosomes: mRNA → protein

• Ribosome = translation

What is the general role of mRNA?

mRNA carries genetic instructions copied from DNA in the nucleus to ribosomes, where the instructions are used to make proteins.

How does DNA determine a protein’s shape and function?

The DNA sequence determines the amino acid sequence of a protein, which determines how the protein folds into its shape and therefore its function.

What are anabolic reactions? Give an example.

Anabolic reactions build larger molecules from smaller molecules and usually require energy.

Easy memory: Anabolic = build up.

What are catabolic reactions? Give an example.

Catabolic reactions break down larger molecules into smaller molecules and often release energy.
Example: Glucose → carbon dioxide + water during cellular respiration.

What is the general role of enzymes in speeding metabolic reactions?

Enzymes are proteins that speed up metabolic reactions by lowering the activation energy needed for the reaction to occur.

Easy memory: Enzymes = speed up reactions.

What is metabolism?

Metabolism is the sum of all anabolic and catabolic reactions that occur in the body.

Easy memory: Metabolism = building + breaking down.

What is a metabolic pathway?

A metabolic pathway is a series of enzyme-catalyzed reactions that occur in a specific sequence to produce a desired product.

Easy memory: Metabolic pathway = enzyme steps → product.

How does feedback inhibition regulate a metabolic pathway?

Feedback inhibition occurs when the final product of a pathway inhibits an earlier enzyme, slowing or stopping the pathway when enough product has been made.

Easy memory: Too much product → pathway slows down.

What is the basic structure of ATP?

ATP (adenosine triphosphate) is made of adenine + ribose sugar + three phosphate groups.

Easy memory: ATP = Adenine + Ribose + 3 Phosphates.

How does ATP store and release energy?

ATP stores usable energy in its phosphate bonds. When ATP loses its third phosphate, it becomes ADP + phosphate (Pᵢ) and releases energy. Energy can be used to add Pᵢ back to ADP, reforming ATP.

What are examples of cellular work powered by ATP?

• Active transport: ATP powers protein pumps that move substances across the membrane against their concentration gradient.

• Muscle contraction: ATP powers myosin movement, causing actin and myosin to slide.

• Synthesis: ATP provides energy to build larger molecules, such as proteins, from smaller molecules.

Why is ATP called the cell’s “energy currency”?

ATP stores and transfers usable energy to power cellular processes. When ATP loses a phosphate group, it releases energy that the cell can use for active transport, muscle contraction, and synthesis.

How does the ATP-ADP cycle work as continuous recharging rather than long-term energy storage?

ATP is constantly used and recharged. When ATP loses a phosphate, it becomes ADP + Pi and releases energy; energy from cellular respiration is then used to add Pi back to ADP, reforming ATP.

How does a cell’s ATP demand relate to its metabolic activity?

Cells with higher metabolic activity require more ATP. For example, muscle cells need lots of ATP for contraction, while fat cells generally have lower ATP demands because they are less energy-demanding at rest.

What are the three main stages of cellular respiration?

• Glycolysis – breaks glucose into pyruvate.

• Citric acid cycle (Krebs cycle) – further breaks down fuel and produces electron carriers.

• Electron transport chain (ETC) – uses electrons to produce most of the cell’s ATP.

Where does glycolysis occur?

Cytoplasm (cytosol)

Where does citric acid/Krebs cycle occur?

Mitochondrial matrix

Where does electron transport chain occur?

Inner mitochondrial membrane

What are the overall inputs and outputs of cellular respiration?

Inputs: Glucose + O₂
Outputs: CO₂ + H₂O + ATP (energy)

Overall: Glucose + O₂ → CO₂ + H₂O + ATP

Easy memory: Food + Oxygen → CO₂ + Water + Energy

What does the glycolysis stage of cellular respiration contribute?

Splits glucose into smaller molecules and produces some ATP and electron carriers.

What does the citric acid/Krebs cycle stage of cellular respiration contribute?

Further breaks down molecules and loads electron carriers (NADH and FADH₂).

What does the citric acid/Krebs cycle stage of cellular respiration contribute?

Further breaks down molecules and loads electron carriers (NADH and FADH₂).

What does the electron transport chain cycle stage of cellular respiration contribute?

Uses the electron carriers to make most of the ATP.

What is glycolysis?

Glycolysis is the first stage of cellular respiration. It splits one glucose molecule into two pyruvate molecules, producing a small amount of ATP and NADH.

What is the citric acid/Krebs cycle?

The citric acid cycle is the second stage of cellular respiration. It breaks down carbon molecules further and produces NADH and FADH₂ (electron carriers), along with a small amount of ATP.

Easy memory: Krebs = break down fuel → load electron carriers.

What is the electron transport chain (ETC)?

The ETC is the third stage of cellular respiration. It uses electrons from NADH and FADH₂ to create a proton gradient that drives ATP production, making most of the cell’s ATP.

Easy memory: ETC = electrons → proton gradient → most ATP.

What is the role of oxygen as the final electron acceptor in the electron transport chain?

Oxygen accepts the electrons at the end of the ETC and combines with H⁺ (hydrogen ions) to form water (H₂O). This allows the electron transport chain to continue running and ATP production to continue.

Easy memory: O₂ = final electron catcher → H₂O.

How much ATP is produced from the complete breakdown of one glucose molecule?

About 30–32 ATP are produced from one glucose molecule during cellular respiration in eukaryotic cells.

What are aerobic and anaerobic respiration?

• Aerobic respiration: Cellular respiration that requires oxygen (O₂) to produce ATP.

• Anaerobic respiration: Energy production that occurs without oxygen (O₂).

How does ATP yield compare between aerobic and anaerobic respiration?

Aerobic respiration produces about 30–32 ATP per glucose, while anaerobic pathways produce only about 2 ATP per glucose

What is the product of anaerobic respiration in human cells?

Human cells produce lactate (lactic acid) when oxygen is limited. This allows glycolysis to continue producing a small amount of ATP.

When do cells rely on anaerobic respiration?

Cells rely more on anaerobic respiration when oxygen is limited, such as during intense exercise when muscles need ATP faster than oxygen can be supplied.

What are the consequences of lactic acid (lactate) buildup?

During intense exercise, increased lactate production is associated with muscle fatigue and a burning sensation. After exercise, the body needs extra oxygen to help restore normal conditions and process the lactate, often described as oxygen debt.

Easy memory: Intense exercise → lactate ↑ → fatigue → extra O₂ needed afterward.

How does oxygen availability affect the electron transport chain?

Oxygen is required for the ETC to keep running because it is the final electron acceptor. When oxygen is unavailable, electrons cannot be passed off at the end of the chain, so the ETC stops and most ATP production stops.

Easy memory: O₂ available → ETC runs → lots of ATP; O₂ absent → ETC stops → little ATP.

What is the body’s primary, preferred fuel source?

Glucose (a carbohydrate) is the body’s primary and preferred fuel because cells can quickly break it down to produce ATP.

How can lipids and proteins be used for energy?

Lipids (fats) and proteins can be broken down and used to produce energy when needed, especially when glucose is limited.

Why do fats yield more energy per gram than carbohydrates?

Fats contain more energy-rich chemical bonds and are more highly reduced than carbohydrates, so their complete breakdown releases more energy.

In general terms, how do fats and proteins feed into the cellular respiration pathways?

• Fats: Broken into fatty acids + glycerol. Fatty acids are broken down into acetyl-CoA, which enters the citric acid cycle.

• Proteins: Broken into amino acids. After removal of the amino group, their remaining parts can enter glycolysis, acetyl-CoA formation, or the citric acid cycle.

When does the body shift toward fats and proteins for fuel?

When glucose availability is low or energy demand is high, the body increases its use of fats and, eventually, proteins.

• Fasting: Liver glycogen decreases → body increases fat breakdown for energy.

• Prolonged exercise: Muscles use more fatty acids as glycogen stores decline.

• Starvation: Fat becomes the major fuel source; the body also breaks down protein to provide amino acids for energy and glucose production.

How do the fuels used in cellular respiration connect to carbohydrates?

Carbohydrates → glucose → glycolysis → ATP

How do the fuels used in cellular respiration connect to lipids?

Lipids → fatty acids + glycerol → acetyl-CoA/glycolysis → Krebs cycle → ATP

How do the fuels used in cellular respiration connect to proteins?

Proteins → amino acids → glycolysis/acetyl-CoA/Krebs → ATP

How do the fuels used in cellular respiration connect to nucleic acids?

Nucleic acids → nucleotides → generally not used as a major energy source