Chapter 4 and 5 Biological Molecules Study Guide

Flashcards covering key concepts, biological molecules, protein structures, nucleic acids, and enzyme activity from Chapters 4 and 5.

What are the defining characteristics of polar, nonpolar, hydrophilic, and hydrophobic substances?

Polar substances have unequal charge distributions and interact with water, while nonpolar substances have equal charge distributions and do not dissolve in water. Hydrophilic substances interact readily with or dissolve in water, whereas hydrophobic substances repel or do not dissolve in water.

What are the three types of isomers and how do their structures differ?

Structural isomers differ in the covalent arrangement of their atoms. Geometric isomers (cis/trans) differ in spatial arrangement around a double bond. Enantiomers are non-superimposable mirror-image isomers.

How do dehydration synthesis and hydrolysis differ?

Dehydration synthesis forms polymers from monomers by removing a water molecule, whereas hydrolysis breaks down polymers into monomers by adding a water molecule.

If given a chemical formula containing C, H, and O, how can you determine whether it is a carbohydrate or a lipid?

Carbohydrates typically have a carbon to hydrogen to oxygen ratio near $1:2:1$ (such as $C_6H_{12}O_6$), whereas lipids contain far fewer oxygen atoms relative to their high numbers of carbon and hydrogen atoms.

What are the monomers, linkages, and primary functions of carbohydrates?

Their monomers are monosaccharides (such as glucose, fructose, galactose, deoxyribose, and ribose). They are joined by glycosidic linkages. Their primary functions include cellular energy source and structural support.

Which monosaccharides combine to form the disaccharides sucrose and maltose?

Sucrose is formed from glucose + fructose. Maltose is formed from glucose + glucose.

What are four major polysaccharides and their primary biological roles?

Glycogen (energy storage in animals), starch (energy storage in plants), cellulose (structural component of plant cell walls), and chitin (structural support in exoskeletons and fungal cell walls).

Why can humans digest starch but not cellulose?

Starch and cellulose have different glycosidic linkage configurations ($\text{alpha}$ vs $\text{beta}$ linkages); human digestive enzymes can hydrolyze the $\text{alpha}$ linkages in starch but cannot break the $\text{beta}$ linkages in cellulose.

What are the major components, linkages, and types of lipids?

Lipids consist of glycerol and fatty acids (or steroid ring structures), connected by ester linkages. Major types include triglycerides (saturated, unsaturated, and trans fats), phospholipids, and steroids like cholesterol.

What functional groups and structural components make up an amino acid?

An amino acid consists of a central alpha carbon bound to an amino group ($\text{-NH}_2$ or $\text{-NH}_3^+$), a carboxyl group ($\text{-COOH}$ or $\text{-COO}^-$), a hydrogen atom, and a variable R group (side chain).

What type of chemical bond links amino acids together in a protein?

Amino acids are joined by peptide bonds, which form between the carboxyl group of one amino acid and the amino group of another.

What are the four levels of protein structure and how is each level stabilized?

Primary structure is the amino acid sequence stabilized by peptide bonds. Secondary structure (alpha-helices and beta-pleated sheets) is stabilized by hydrogen bonds along the backbone. Tertiary structure is the 3D shape stabilized by R group interactions (hydrogen bonds, ionic bonds, hydrophobic interactions, disulfide bridges). Quaternary structure consists of multiple polypeptide subunits stabilized by R group interactions.

What is protein denaturation and what factors cause it?

Denaturation is the loss of a protein's functional three-dimensional shape without breaking primary peptide bonds. It is caused by factors such as changes in pH, extreme temperature, or high salt concentrations.

What components are found in all nucleotides?

All nucleotides contain a 5-carbon sugar (ribose or deoxyribose), a nitrogenous base, and a phosphate group.

How do DNA and RNA differ in their sugar, nitrogenous bases, and strandedness?

DNA contains deoxyribose sugar, thymine (T), and is double-stranded. RNA contains ribose sugar, uracil (U), and is single-stranded.

What is the flow of genetic information in a cell?

The flow of genetic information follows the pathway: $\text{DNA} \rightarrow \text{mRNA} \rightarrow \text{protein}$.

If a sample of DNA contains $30\text{\%}$ thymine (T), what is the percentage of cytosine (C)?

The percentage of cytosine (C) is $20\text{\%}$. Since thymine is $30\text{\%}$, adenine is also $30\text{\%}$ (total A+T = $60\text{\%}$). The remaining $40\text{\%}$ is divided equally between cytosine and guanine.

How do competitive and noncompetitive enzyme inhibitors differ?

Competitive inhibitors bind directly to the enzyme's active site, competing with the substrate. Noncompetitive inhibitors bind to an allosteric site (a site other than the active site), changing the enzyme's shape and reducing its activity.

According to the test diagram notes, what element uniquely characterizes amino acids among biological building blocks?

Nitrogen.

Polar vs. nonpolar substances

Polar substances have unequal charge distribution and interact with water, while nonpolar substances have equal charge distribution and do not dissolve in water.

Hydrophilic vs. hydrophobic substances

Hydrophilic substances interact readily with or dissolve in water, whereas hydrophobic substances repel or do not dissolve in water.

Structural isomers

Molecules that have the same molecular formula but differ in the covalent arrangement of their atoms.

Geometric (cis/trans) isomers

Isomers that differ in their spatial arrangement around a double bond.

Enantiomers

Isomers that are non-superimposable mirror images of each other.

Dehydration synthesis

A chemical reaction that forms polymers from monomers by removing a water molecule.

Hydrolysis

A chemical reaction that breaks polymers down into monomers by adding a water molecule.

Distinguishing carbohydrates from lipids by chemical formula

Carbohydrates have a carbon to hydrogen to oxygen ratio near $1:2:1$ (such as $C<em>6H</em>{12}O_6$), whereas lipids contain far fewer oxygen atoms relative to carbon and hydrogen.

Carbohydrate monomers and linkages

Monomers are monosaccharides (e.g., glucose, fructose), joined together by glycosidic linkages.

Disaccharides: sucrose and maltose composition

Sucrose is composed of glucose + fructose. Maltose is composed of glucose + glucose.

Roles of glycogen and starch

Glycogen provides energy storage in animals, while starch provides energy storage in plants.

Roles of cellulose and chitin

Cellulose provides structural support in plant cell walls, while chitin provides structural support in exoskeletons and fungal cell walls.

Digestibility of starch vs. cellulose

Humans can hydrolyze the $\text{alpha}$ linkages in starch, but cannot break the $\text{beta}$ linkages in cellulose.

Basic structure and linkage of lipids

Composed of glycerol and fatty acids (or steroid ring structures) connected by ester linkages.

Three major types of lipids

Triglycerides (saturated, unsaturated, trans fats), phospholipids, and steroids.

Four components of an amino acid

A central alpha carbon bound to an amino group ($\text{-NH}_2$), a carboxyl group ($\text{-COOH}$), a hydrogen atom, and a variable R group.

Peptide bond

A covalent bond joining the carboxyl group of one amino acid to the amino group of another.

Primary protein structure

The linear sequence of amino acids stabilized by peptide bonds.

Secondary protein structure

Coils and folds ($\text{alpha}$-helices and $\text{beta}$-pleated sheets) stabilized by hydrogen bonds along the polypeptide backbone.

Tertiary protein structure

The overall 3D shape of a single polypeptide, stabilized by interactions between R groups.

Quaternary protein structure

The structure formed by multiple polypeptide subunits interacting via R group interactions.

Protein denaturation

The loss of a protein's functional 3D shape without breaking primary peptide bonds, caused by changes in pH, extreme temperature, or high salt concentrations.

Three components of a nucleotide

A $5$-carbon sugar (ribose or deoxyribose), a nitrogenous base, and a phosphate group.

Structural differences between DNA and RNA

DNA contains deoxyribose, thymine (T), and is double-stranded. RNA contains ribose, uracil (U), and is single-stranded.

Central dogma of molecular biology

The flow of genetic information: $\text{DNA} \rightarrow \text{mRNA} \rightarrow \text{protein}$

Calculating DNA base percentages (Chargaff's rules)

If DNA has $30\text{\%}$ thymine (T), it also has $30\text{\%}$ adenine (A). The remaining $40\text{\%}$ is split equally between cytosine (C = $20\text{\%}$) and guanine (G = $20\text{\%}$).

Competitive vs. noncompetitive enzyme inhibitors

Competitive inhibitors bind directly to the active site, competing with the substrate. Noncompetitive inhibitors bind to an allosteric site, altering enzyme shape.

Characteristic element in amino acids

Nitrogen uniquely characterizes amino acids among basic biological building blocks.