Biochemistry: Proteins and Nucleic Acids

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Questions and Answers

What is the primary function of disulfide bridges in proteins?

They enhance protein flexibility.

They link two cysteine amino acids via covalent bonds. (correct)

They minimize protein-protein interactions.

They serve as an energy source.

Which statement about proteins and their domains is accurate?

Domains within proteins do not influence their functions.

Proteins sharing a domain also share a specific function. (correct)

Domains are unrelated to the protein structure.

All proteins have exactly one domain.

What distinguishes DNA from RNA?

RNA has one form, while DNA has multiple forms.

DNA contains uracil; RNA does not.

DNA uses deoxyribose and RNA uses ribose. (correct)

RNA is a double helix, while DNA is single-stranded.

Which of the following is a component of a nucleotide?

Phosphate group Signup and view all the answers

How many strands does DNA typically consist of?

Two strands Signup and view all the answers

What is the role of RNA in regard to genetic information?

It decodes genetic information for protein synthesis. Signup and view all the answers

Which base is found in RNA but not in DNA?

Uracil Signup and view all the answers

What characterizes the sugar-phosphate backbone of nucleic acids?

It provides structural support to the nucleic acid. Signup and view all the answers

What property of carbon makes it a fundamental element in organic molecules?

It can form covalent bonds with a variety of elements. Signup and view all the answers

Which of the following is NOT a class of macromolecules?

Salts Signup and view all the answers

What process occurs during the formation of a polymer from its monomers?

Dehydration Signup and view all the answers

What determines the shape and function of proteins?

The sequence of amino acids and interactions between them Signup and view all the answers

Which statement best describes the difference between DNA and RNA?

DNA contains deoxyribose, while RNA contains ribose. Signup and view all the answers

Which of the following components is NOT part of a nucleotide?

An amino acid Signup and view all the answers

Which type of bonding is always found in organic molecules?

Covalent bonding Signup and view all the answers

What is the role of hydrolysis in macromolecule metabolism?

To break down polymers into monomers Signup and view all the answers

What is the primary function of glycogen in animal cells?

Short-term energy storage Signup and view all the answers

Which component of starch is a polymer of glucose that plants use for storing excess glucose?

Amylopectin Signup and view all the answers

What is the common structural role of cellulose?

Cell wall component in plants Signup and view all the answers

What hormonal action promotes the storage of glucose as glycogen?

Insulin release Signup and view all the answers

What is a defining feature of lipids?

Nonpolar and insoluble in water Signup and view all the answers

What type of reaction forms triglycerides from glycerol and fatty acids?

Dehydration Signup and view all the answers

What type of carbohydrate is chitin primarily associated with?

Fungi and external skeletons of insects Signup and view all the answers

What distinguishes glycosaminoglycans from other polysaccharides?

Presence of sulfate groups Signup and view all the answers

Which of the following statements accurately describes saturated fatty acids?

All carbons are linked by single covalent bonds. Signup and view all the answers

What is the primary function of fats in biological systems?

To provide energy storage. Signup and view all the answers

Phospholipids are unique because they contain:

A polar phosphate group. Signup and view all the answers

Which of the following correctly identifies the role of cholesterol in relation to other steroids?

Cholesterol is the precursor of several other steroids. Signup and view all the answers

What is characteristic of unsaturated fatty acids?

They contain two or more double bonds. Signup and view all the answers

Which structure is primarily formed by phospholipids in a cell membrane?

A phospholipid bilayer. Signup and view all the answers

What distinguishes waxes from other lipids?

They are extremely nonpolar with a high melting point. Signup and view all the answers

How do testosterone and estrogen differ structurally?

They have different functionalities attached to the same carbon skeleton. Signup and view all the answers

What is the primary role of hemoglobin in the body?

Transportation of oxygen Signup and view all the answers

Which group of amino acids is characterized by side chains that do not interact favorably with water?

Hydrophobic (nonpolar) Signup and view all the answers

Which type of bond is formed between amino acids during peptide bond formation?

Covalent bond Signup and view all the answers

What determines the tertiary structure of a protein?

Chemical and physical interactions Signup and view all the answers

Which factor is NOT involved in promoting protein folding and stability?

Dehydration reactions Signup and view all the answers

The primary structure of a protein refers to what?

Sequence of amino acids Signup and view all the answers

What type of interaction stabilizes the secondary structure of proteins?

Hydrogen bonds Signup and view all the answers

Which of the following groups of amino acids is involved in interactions that promote protein folding?

Hydrophilic (polar) amino acids Signup and view all the answers

Study Notes

Disulfide Bridges

Covalent bonds linking two cysteine amino acids containing sulfhydryl groups.

Protein-Protein Interactions

Many cellular processes involve interactions between two or more proteins.
Highly specific binding occurs at the protein surface.

Domains in Proteins

Modules or domains within proteins have distinct structures and functions.
The signal transducer and activator of transcription (STAT) protein is an example.
Each domain of this protein is involved in a distinct biological function.
Proteins sharing a domain also share that function.

Nucleic Acids

Responsible for storing, expressing, and transmitting genetic information.
Two classes: Deoxyribonucleic acid (DNA) and Ribonucleic acid (RNA).
DNA stores genetic information encoded in the sequence of its monomer building blocks.
RNA decodes this information into instructions for polypeptide chain formation.
The monomer of nucleic acids is a nucleotide.
Nucleotides consist of a phosphate group, a 5-carbon sugar (ribose or deoxyribose), and a nitrogenous base.
The sugar-phosphate backbone forms the structure of nucleic acids.

DNA Structure

DNA exists as a double-stranded helix.

DNA vs. RNA

DNA: Deoxyribonucleic acid, contains deoxyribose sugar, thymine base, double-stranded, one form.
RNA: Ribonucleic acid, contains ribose sugar, uracil base, single-stranded, several forms.
Adenine (A), guanine (G), and cytosine (C) are found in both DNA and RNA.

Organic Chemistry

Organic molecules contain carbon (C) and hydrogen (H).
Organic molecules are abundant in living organisms.
Macromolecules are large, complex organic molecules.

Four Categories of Macromolecules

Carbohydrates
Lipids
Proteins
Nucleic Acids

Organic vs. Inorganic Molecules

Inorganic Molecules: Usually contain positive and negative ions, ionic bonding, small number of atoms, associated with non-living matter.
Organic Molecules: Always contain carbon and hydrogen, covalent bonding, often large with many atoms, usually associated with living organisms.

Polymer Formation

Polymers are made up of monomers.
Dehydration reaction: Removal of a water molecule, forming polymers.
Hydrolysis: Addition of a water molecule, breaking down polymers.

Carbohydrates (Polysaccharides) - Energy Storage

Starch: Mixture of amylose and amylopectin, both glucose polymers. Used by plants for glucose storage.
Glycogen: Animals store glucose as glycogen (granules in liver). Polysaccharide of glucose for short-term energy storage in animal cells.
Hormonal Regulation: Insulin promotes glucose storage as glycogen, while glucagon stimulates glycogen breakdown into glucose.

Carbohydrates (Polysaccharides) - Structural Role

Cellulose: Most abundant carbohydrate, polymer of β-glucose. Found in plant cell walls.
Chitin: Forms external skeletons in insects and cell walls in fungi. Sugar monomers have nitrogen-containing groups.
Glycosaminoglycans: Found in animals, abundant in cartilage. Sugar monomers have carboxyl and sulfate groups.

Lipids

Organic molecules composed mainly of H and C atoms (hydrocarbon chains).
Nonpolar, making them insoluble in water.
Used for insulation and long-term energy storage in animals.
Plants use oils for long-term energy storage.
Other important lipids include phospholipids and steroids.

Lipids: Fats

Mixture of triglycerides (triacylglycerols), long-term energy storage.
Formed by bonding glycerol to three fatty acids through dehydration or condensation reactions.
Broken apart by hydrolysis.
Glycerol has three OH groups, making it soluble in water.
Fatty acids have a long hydrocarbon chain with a carboxyl group at one end.
Fat and oil formation occurs when the acidic portions of fatty acids react with glycerol during a dehydration reaction.

Lipids: Fats (continued)

Fatty acids can be saturated or unsaturated.
Saturated fatty acids: No double bonds between carbon atoms, all carbons linked by single bonds, tend to be solid at room temperature.
Unsaturated fatty acids: Contain one or more double bonds in the carbon chain (monounsaturated: 1 double bond, polyunsaturated: 2+ double bonds), tend to be liquid at room temperature (plant oils).
Fats are important for energy storage (1 gram of fat stores twice as much energy as 1 gram of glycogen or starch).
Fats can also be structural, providing cushioning and insulation.

Lipids: Phospholipids

Membrane components.
Contain a phosphate group.
Instead of a third fatty acid attached to glycerol, there is a polar phosphate group.
Amphipathic molecule: hydrophilic heads (phosphate region) and hydrophobic tails (fatty acid chains).
Polar heads arrange themselves adjacent to water.
The bulk of the cell plasma membrane consists of a phospholipid bilayer.

Lipids: Steroids

Have a skeleton of four interconnected carbon rings.
Usually not very water soluble.
Examples: cholesterol, estrogen, and testosterone.
Cholesterol is the precursor of several other steroids.

Lipids: Waxes

Long-chain fatty acid bonded to a long-chain alcohol.
Secreted onto plant leaves and insect cuticles.
Very nonpolar and exclude water, providing a barrier to water loss.
High melting point, solid at normal temperature.
Waterproof and resistant to degradation.
Structural elements in colonies (bee hives).

Proteins

Diverse functions:
- Support: keratin (hair, nails, ligaments)
- Enzymes: bring reactants together.
- Transport: channel and carrier proteins (plasma membrane), allow substances to enter and exit cells. Hemoglobin transports oxygen.
- Defense: antibodies combine with foreign substances and prevent them from destroying cells.
- Hormones: eg. Insulin regulates blood glucose.
- Motion: eg. Actin and myosin allow cell parts to move and cause muscles to contract.
Composed of C, H, O, N, and small amounts of other elements, notably S.
Amino acids are the monomers of proteins.
Common structure with a variable R-group.
Twenty different amino acids.
Side chains determine structure and function.
Each amino acid contains a hydrogen atom, an amino group (-NH2), an acidic group (-COOH), and an R group.

Proteins: Amino Acid Structure

Classified into four groups based on side chain properties: acidic, basic, hydrophilic (polar), and hydrophobic (nonpolar).

Proteins: Peptide Bond Formation

Amino acids joined by dehydration or condensation reactions through a covalent bond called a peptide bond.
Peptide: Two or more amino acids bonded together.
Polypeptide: Chain of many amino acids joined by peptide bonds.
Proteins: Made up of one or more polypeptides.
Peptide bonds are broken apart by hydrolysis.

Protein Structure

Primary structure: Sequence of amino acids, determined by genes.
Secondary structure: Chemical and physical interactions cause folding. Includes α helices, β pleated sheets, and "random coiled regions."
Tertiary structure: Folding and twisting resulting in the final three-dimensional shape of a polypeptide.
Quaternary structure: Consists of more than one polypeptide.

Factors Promoting Protein Folding and Stability

Hydrogen bonds: Promote protein folding and stability.
Ionic bonds: Ionic and polar interactions promote folding and stability.
Hydrophobic effects: Avoid water contact.
Van der Waals forces: Weak attractions between atoms.
Disulfide bridges: Covalent bonds between cysteine residues in the polypeptide chain.

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Description

Explore the essential concepts of biochemistry focusing on proteins and nucleic acids. Understand the significance of disulfide bridges, protein interactions, and the role of nucleic acids in genetic information storage and transmission. This quiz will test your knowledge of protein domains and the functions of DNA and RNA.