MCAT Biology Practice Questions

Questions and Answers

What is the chemical reaction that breaks down all the major macromolecules?

Hydrolysis

What is the strongest type of intermolecular bond?

Hydrogen bonds

Why is water a liquid at high temperatures?

Hydrogen bonding holds the water molecules closer together.

What is an amphipathic molecule? Give an example.

A molecule with both hydrophobic and hydrophilic regions. Example: Phospholipid. Signup and view all the answers

What is a lipid?

A biological molecule with low solubility in water. Signup and view all the answers

What are the 6 major groups of lipids?

Fatty acids, Tri-glycerides, Phospholipids, Glycolipids, Steroids, Terpenes. Signup and view all the answers

What is the structure of a tri-glyceride?

Tri-glycerides are esters composed of a 3-carbon glycerol backbone and 3 fatty acid chains. Signup and view all the answers

What happens if you add water to an ester group in a tri-glyceride?

Water cleaves the ester bond into an alcohol and a carboxylic fatty acid. Signup and view all the answers

What is important to know about the longer carbon chains in a tri-glyceride regarding water solubility?

Longer carbon chains are less water soluble. Signup and view all the answers

How soluble are shorter chain fatty acids?

Shorter chain fatty acids are slightly water soluble. Signup and view all the answers

What is special about saturated fatty acids regarding their melting point?

Saturated fatty acids have only single bonds along the carbon chain and a higher melting point. Signup and view all the answers

What is special about unsaturated fatty acids regarding their melting point?

Unsaturated fatty acids have at least one double bond and a lower melting point. Signup and view all the answers

Explain the phospholipids structure.

Phospholipids are built on a 3-carbon backbone with one phosphate group and two carbon chains. Signup and view all the answers

What regions are polar and nonpolar in a membrane?

Polar phosphate regions face outside; nonpolar carbon chains face inside. Signup and view all the answers

Explain glycolipids structure.

Glycolipids have a 3-carbon backbone with 2 carbon chains and a carbohydrate attached. Signup and view all the answers

What do steroids look like?

Slightly amphipathic 4-ring structures. Signup and view all the answers

How do lipids move through the blood despite being insoluble?

They are usually carried by lipoproteins like HDL or LDL. Signup and view all the answers

What are the major classes of lipoproteins?

Chylomicrons, VLDLs, LDLs, HDLs. Signup and view all the answers

What are proteins made up of?

One or more chains of amino acids. Signup and view all the answers

Describe amino acid structure.

Amino acids have an amino group, R group, carboxylic acid, and hydrogen. Signup and view all the answers

What are the basic amino acids?

Histidine, Arginine, Lysine. Signup and view all the answers

What are the acidic amino acids?

Aspartic acid and Glutamic acid. Signup and view all the answers

What are the nonpolar amino acids?

Phenylalanine, Leucine, Tryptophan, Methionine, Glycine, Isoleucine, Valine, Alanine, Proline. Signup and view all the answers

What is the primary structure of a protein?

Sequence of amino acids and location of disulfide bonds. Signup and view all the answers

What is the secondary structure of a protein?

Twisting of the alpha helix and beta sheets. Signup and view all the answers

What is the tertiary structure of a protein?

3D structure including bending. Signup and view all the answers

What is the quaternary structure of a protein?

Multiple proteins in formation. Signup and view all the answers

What are the five forces that create tertiary structure?

Covalent, Disulfide bonding, Hydrogen bonds, Hydrophobic, Van der Waals. Signup and view all the answers

What levels of structure are disrupted during the denaturation process?

Secondary to quaternary structures. Signup and view all the answers

What is the difference between a proteoglycan and a glycoprotein?

Glycoproteins have a higher protein to carbohydrate ratio; proteoglycans have more carbohydrates. Signup and view all the answers

What is the empirical formula for any carbohydrate?

CH2O Signup and view all the answers

Describe the chemical structure of glucose.

Aldehyde with 4 chiral carbons in a 6-membered ring. Signup and view all the answers

Where is glucose stored in alpha linkages?

In animals as glycogen and in plants as starch. Signup and view all the answers

Who stores glucose with beta linkages?

In plant cell walls as cellulose. Signup and view all the answers

What molecule is added to glycogen, starch, and cellulose to break off individual glucose molecules?

Water via hydrolysis reaction. Signup and view all the answers

What are the four macromolecules?

Proteins, Lipids, Carbohydrates, Nucleic acids. Signup and view all the answers

What are the three parts of a nucleotide?

Ribose sugar, Nitrogenous base, PO4 group. Signup and view all the answers

What molecule breaks up nucleic acids into nucleotides?

Water with the help of nucleases. Signup and view all the answers

What are some other important nucleotides?

FADH, NADH, ATP, cyclic AMP. Signup and view all the answers

What are minerals?

Inorganic elements that function to establish electrochemical gradients and act as cofactors. Signup and view all the answers

What are enzymes?

Typically proteins that increase reaction rates by lowering activation energy. Signup and view all the answers

What is activation energy?

Energy needed to break the bonds of reactants to create the transition state. Signup and view all the answers

An enzyme is typically larger than the substrate.

True Signup and view all the answers

Where does a substrate attach to an enzyme?

At the active site. Signup and view all the answers

What are the two hypotheses of enzyme and substrate interactions?

Lock and key model, Induced fit model. Signup and view all the answers

One enzyme is tailor-made for one reaction.

True Signup and view all the answers

What are saturation kinetics?

Reaction rate increases with substrate until saturation is reached. Signup and view all the answers

What factors affect enzymatic reactions?

Optimal temperature and optimal pH. Signup and view all the answers

How do cells regulate enzymes?

By inhibition and producing inactive forms, activated when needed. Signup and view all the answers

What are the general types of enzyme inhibition?

Feedback inhibition and chemical inhibition. Signup and view all the answers

What is feedback inhibition?

When a product of a reaction inhibits an earlier enzyme in the chain. Signup and view all the answers

What are specific ways in which enzymes are inhibited?

Competitive, non-competitive, and irreversible inhibition. Signup and view all the answers

What is competitive inhibition?

Inhibitors compete for the active site. Signup and view all the answers

What is non-competitive inhibition?

Inhibitors change the enzyme's shape, reducing substrate affinity. Signup and view all the answers

What is irreversible inhibition?

Something covalently bonds to the active site and cannot be removed. Signup and view all the answers

What is respiration?

The energy-requiring stages of metabolism. Signup and view all the answers

Where does glycolysis take place?

In the cytosol of the cell. Signup and view all the answers

Does glycolysis require oxygen?

False Signup and view all the answers

Is glycolysis poisoned by oxygen?

False Signup and view all the answers

What is the net ATP produced by glycolysis?

2 ATP, 2 NADH, 2 3C pyruvates. Signup and view all the answers

What happens to the NADHs at the end of glycolysis if oxygen is not present?

NADHs are oxidized back to NAD+ through fermentation. Signup and view all the answers

If oxygen is present, what happens to the products of glycolysis?

They enter the mitochondria. Signup and view all the answers

What is the energy cost of transporting one NADH into the mitochondria?

1 ATP per NADH. Signup and view all the answers

How many ATPs does each NADH produce during the electron transport chain (ETC)?

Each NADH produces 3 ATPs via ETC. Signup and view all the answers

In the mitochondrial matrix, what happens to the pyruvates?

Each pyruvate is converted to acetyl-CoA. Signup and view all the answers

What are the energetic products of the TCA cycle?

1 ATP, 3 NADH, 1 FADH. Signup and view all the answers

Overall, aerobic respiration of a single glucose molecule results in a net of how many ATPs?

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What is the electron transport chain (ETC)?

A series of proteins that pass electrons and pump protons. Signup and view all the answers

What is aerobic respiration?

Oxidation or combustion of glucose. Signup and view all the answers

What is the final electron acceptor in the ETC?

Oxygen. Signup and view all the answers

How are tri-glycerides burned for energy?

Tri-glycerides are broken down into fatty acids and glycerol. Signup and view all the answers

How are proteins burned for energy?

Amino acids enter at various portions, depending on the amino acid. Signup and view all the answers

What is the rule of the ratio of gene to polypeptide?

One gene makes one polypeptide. Signup and view all the answers

How many copies of a gene do prokaryotes have?

One. Signup and view all the answers

For most genes, how many copies do eukaryotes have?

One copy, but some genes can have multiple copies. Signup and view all the answers

What are the three main components of a nucleotide?

Nitrogenous base, pentose sugar, PO4 group. Signup and view all the answers

What are the four nitrogenous bases?

Adenine, Thymine, Cytosine, Guanine. Signup and view all the answers

What are the four nucleosides?

Adenosine, Cytidine, Guanosine, Thymidine. Signup and view all the answers

What is the difference between a nucleotide and a nucleoside?

Nucleosides are nucleotides without the three phosphate groups. Signup and view all the answers

What are the purines?

Adenine and Guanine. Signup and view all the answers

What are the pyrimidines?

Cytosine and Thymine. Signup and view all the answers

Which carbon is the PO4 group attached to?

The 5th carbon on each pentose sugar. Signup and view all the answers

What kind of bond connects the PO4 group to the 3rd carbon on the pentose sugar of the nucleotide chain?

Phosphodiester bond. Signup and view all the answers

In a phosphodiester bond, which numbered carbons are connected?

The 3rd carbon on one nucleotide and the 5th carbon on another. Signup and view all the answers

How do the nitrogenous bases bond to each other?

Through hydrogen bonds. Signup and view all the answers

How many bonds are formed between A and T?

<ol start="2"> <li></li> </ol> Signup and view all the answers

How many bonds are formed between C and G?

<ol start="3"> <li></li> </ol> Signup and view all the answers

Why is replication semi-conservative?

Each original strand pairs with a newly synthesized strand. Signup and view all the answers

In what direction does replication occur?

Bidirectional. Signup and view all the answers

What enzyme separates the two strands of DNA?

DNA helicase. Signup and view all the answers

In what direction does DNA polymerase move?

3' to 5'. Signup and view all the answers

In what direction does DNA polymerase polymerize the complementary strand?

5' to 3'. Signup and view all the answers

In what direction does the replisome move?

It follows the direction of the unzipping strand. Signup and view all the answers

What is the replisome composed of?

Two polymerase complexes and various associated proteins. Signup and view all the answers

Which polymerase polymerizes the leading strand?

Pol delta. Signup and view all the answers

Which polymerase polymerizes the lagging strand?

Pol alpha. Signup and view all the answers

What are Okazaki fragments?

Short DNA fragments synthesized on the lagging strand. Signup and view all the answers

How does RNA differ from DNA?

RNA contains ribose, is single-stranded, and has uracil instead of thymine. Signup and view all the answers

What are the types of RNA?

mRNA, tRNA, rRNA. Signup and view all the answers

Where is RNA synthesized?

In the nucleus. Signup and view all the answers

Study Notes

Hydrolysis and Macromolecules

Hydrolysis is the chemical reaction responsible for breaking down major macromolecules into their smaller components.

Inter-molecular Bonds

Hydrogen bonds are the strongest type of intermolecular bonds, while dipole-dipole and Van der Waals forces are weaker.

Water Characteristics

Water remains a liquid at high temperatures due to hydrogen bonding, which keeps molecules closely packed.

Ampipathic Molecules

Ampipathic molecules possess both hydrophobic and hydrophilic regions; example: Phospholipid (hydrophilic phosphate group and hydrophobic lipid tails).

Lipids

Lipids are biological molecules characterized by low solubility in water, commonly referred to as fats.

Major Groups of Lipids

Key classes of lipids include:
- Fatty acids
- Triglycerides
- Phospholipids
- Glycolipids
- Steroids
- Terpenes (e.g., pine oils, vitamin A).

Structure of Triglycerides

Triglycerides consist of a glycerol backbone with three fatty acid chains linked via ester bonds.

Hydrolysis of Triglycerides

Adding water to triglycerides hydrolyzes ester bonds, yielding glycerol and fatty acids, a reaction accelerated by lipases.

Solubility of Fatty Acids

Longer carbon chains in triglycerides decrease water solubility due to less significant polar carboxylic groups.

Short vs. Long Chain Fatty Acids

Short-chain fatty acids exhibit slight water solubility, while longer chains are significantly less soluble.

Saturated vs. Unsaturated Fatty Acids

Saturated fatty acids contain solely single bonds, resulting in a straight chain and higher melting points due to stronger Van der Waals forces.
Unsaturated fatty acids have one or more double bonds, yielding a lower melting point and potentially oily consistency at room temperature.

Phospholipids Structure

Phospholipids have a glycerol backbone, with one carbon attached to a phosphate group and two fatty acid chains, forming a bilayer in cell membranes.

Membrane Regions

In membranes, polar phosphate regions face outward (hydrophilic), while nonpolar fatty acid chains face inward (hydrophobic).

Glycolipids

Glycolipids include a glycerol backbone with two fatty acid chains and a carbohydrate attached to one carbon.

Steroids

Steroids are characterized by slightly amphipathic four-ring structures.

Lipid Transport in Blood

Lipids are transported in the bloodstream via lipoproteins like HDL and LDL.

Classes of Lipoproteins

Major lipoprotein classes include:
- Chylomicrons (largest)
- VLDLs (very low density)
- LDLs (low density)
- HDLs (high density and smallest).

Protein Composition

Proteins consist of one or more polypeptide chains formed by amino acids.

Amino Acid Structure

Amino acids comprise four components:
- Amino group (NH2)
- R group (20 possible variations)
- Carboxylic acid group (COOH)
- Hydrogen atom.

Basic and Acidic Amino Acids

Basic amino acids: Histidine, Arginine, Lysine.
Acidic amino acids: Aspartic acid, Glutamic acid.

Nonpolar Amino Acids

Nonpolar amino acids include Phenylalanine, Leucine, Tryptophan, Methionine, Glycine, Isoleucine, Valine, Alanine, and Proline.

Protein Structures

Primary structure: Sequence of amino acids and disulfide bond locations.
Secondary structure: Includes alpha helices and beta sheets.
Tertiary structure: 3D shape formed by folding.
Quaternary structure: Assembly of multiple polypeptide chains.

Forces in Tertiary Structure

Key forces creating tertiary structure include covalent bonds, disulfide bridges, hydrogen bonds, hydrophobic interactions, and Van der Waals forces.

Denaturation Effects

Denaturation disrupts secondary through quaternary structures.

Glycoproteins vs. Proteoglycans

Glycoproteins: Made mostly of protein; involved in cell signaling.
Proteoglycans: Rich in carbohydrates; serve as structural components.

Carbohydrate Empirical Formula

General empirical formula for carbohydrates is CH2O.

Glucose Structure

Glucose is an aldehyde with four chiral centers, existing as a six-membered ring.

Glucose Storage

Animals store glucose in glycogen (alpha linkages); plants store it in starch.

Cellulose Structure

Plant cell walls contain cellulose, characterized by beta linkages.

Hydrolysis Reaction

Water breaks glycosidic bonds in glycogen, starch, and cellulose, aided by enzymes like amylase.

Four Major Macromolecules

The primary macromolecules are proteins, lipids, carbohydrates, and nucleic acids.

Nucleotide Composition

Nucleotides consist of ribose sugar, a nitrogenous base, and a phosphate group.

Nucleic Acid Breakdown

Nucleic acids are hydrolyzed to nucleotides using water and the aid of nucleases.

Important Nucleotides

Key nucleotides include FADH, NADH, ATP, and cyclic AMP.

Mineral Functions

Minerals are inorganic elements essential for:
- Establishing electrochemical gradients
- Acting as cofactors for proteins
- Forming bone matrix compounds.

Enzyme Characteristics

Enzymes primarily consist of proteins that accelerate reactions by lowering activation energy.

Activation Energy Definition

The energy required to break reactant bonds and transition into the product state.

Substrate Interaction

Substrates bind to enzymes at the active site, which is typically larger than the substrate.

Enzyme Models

Two hypothesized models for enzyme-substrate interaction:
- Lock and Key Model
- Induced Fit Model.

Enzyme Specificity

Each enzyme is uniquely designed for a specific reaction, enhancing cellular control.

Saturation Kinetics

Reaction rates increase with substrate availability until enzyme saturation is reached.

Enzyme Regulation Factors

Enzyme activity is influenced by optimal temperature and pH levels.

Enzyme Regulation Methods

Cells regulate enzyme function through:
- Inhibition mechanisms
- Production of inactive forms that activate when required.

Types of Enzyme Inhibition

Inhibition classifications include feedback inhibition and chemical inhibition (e.g., poisons).

Competitive vs. Non-competitive Inhibition

Competitive inhibition involves competing for the active site, while non-competitive inhibition modifies enzyme shape, reducing substrate affinity.

Irreversible Inhibition

Irreversible inhibitors covalently bind to the active site, making it permanently inactive.

Respiration Definition

Respiration encompasses energy-requiring metabolic stages.

Glycolysis Location

Glycolysis occurs in the cytosol and does not require oxygen.

Glycolysis Products

Net yield from glycolysis includes 2 ATP, 2 NADH, and 2 pyruvate molecules.

Anaerobic Fate of NADHs

In the absence of oxygen, NADH is oxidized back to NAD+ via fermentation, yielding CO2 and either ethanol or lactic acid.

Aerobic Fate of Glycolysis Products

In aerobic conditions, glycolysis products transition into the mitochondria.

Mitochondrial NADH Transport Cost

Transporting each NADH into the mitochondria requires 1 ATP.

ATP Yield from NADH

Each NADH generates 3 ATPs during the electron transport chain (ETC).

Pyruvate to Acetyl-CoA Conversion

Pyruvates are converted to acetyl-CoA in the mitochondrial matrix, feeding into the TCA cycle.

TCA Cycle Products

Energetic outputs from the TCA cycle include 1 ATP, 3 NADH, and 1 FADH.

Total ATP from Aerobic Respiration

Aerobic respiration of one glucose molecule yields a total of 36 ATP.

Electron Transport Chain Overview

The ETC consists of cytochrome proteins in the mitochondrial inner membrane that pass high-energy electrons, creating a proton gradient for ATP synthesis.

Final Electron Acceptor

Oxygen serves as the final electron acceptor in the ETC.

Fatty Acid Metabolism

Triglycerides are metabolized into fatty acids and glycerol; glycerol enters glycolysis, while fatty acids convert to acetyl-CoA in the mitochondria.

Protein Metabolism

Amino acids enter metabolic pathways at varying points, depending on their specific structure.

Gene to Polypeptide Ratio

Each gene typically results in the production of one polypeptide.

Gene Copies in Prokaryotes

Prokaryotes generally possess one copy of each gene.

Gene Copies in Eukaryotes

Eukaryotes generally have one copy of most genes, with some exceptions (e.g., tRNA and rRNA).

Nucleotide Composition Reiterated

A nucleotide consists of a nitrogenous base, a pentose sugar, and a phosphate group.

Nitrogenous Bases and Nucleosides

Four nitrogenous bases: Adenine, Thymine, Cytosine, Guanine.
Four nucleosides: Adenosine, Cytidine, Guanosine

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Test your knowledge of biology with these MCAT practice flashcards. Each card covers key concepts such as hydrolysis and intermolecular bonds, essential for understanding biological processes. Perfect for reviewing before your MCAT exam.