ACT Biology Study Notes - Biological Molecules

A complete set of 100 practice flashcards reviewing biological molecules, chemical bonding, water properties, pH, buffers, carbohydrates, lipids, proteins, enzymes, and nucleic acids based on the ACT biology lecture notes.

What are isotopes?

Atoms of one element that vary only in the number of neutrons.

How do isotopes of the same element compare regarding atomic number?

They have the exact same atomic number.

How do isotopes of the same element compare regarding mass number?

They have different mass numbers.

How many protons and neutrons are in a carbon-12 atom?

It has $6$ protons and $6$ neutrons.

How many protons and neutrons are in a carbon-14 atom?

It has $6$ protons and $8$ neutrons.

What radioactive isotope is used for the treatment of thyroid cancer?

I-131

Which gland in the body is treated using the radioactive isotope I-131?

Thyroid gland

Which radioactive isotope is used to measure the age of fossils in carbon dating?

C-14

What is a hydrogen bond?

An attraction between a slightly positive hydrogen atom and a slightly negative oxygen, fluorine, or nitrogen atom of another molecule.

Which three electronegative atoms can participate in a hydrogen bond with hydrogen?

Oxygen, fluorine, or nitrogen

What molecular structure interaction is shown in this diagram?

Hydrogen Bonds Structure

Why do large bodies of water like oceans resist sudden changes in temperature?

Because water has a high specific heat.

What property of water refers to large bodies of water absorbing heat and resisting temperature changes?

High specific heat

What is high heat of vaporization in relation to water?

A relatively great amount of heat is needed to evaporate water.

What property of water contributes to capillary action in plants?

High adhesion properties

How does water's high adhesion property help plants?

It contributes to capillary action, which helps water flow up from the roots of a plant to the leaves.

How does water move up a tall tree from roots to leaves without expending energy?

By transpiration pull cohesion tension.

What phenomenon is caused by water's strong cohesion tension?

Surface tension

Why is water referred to as the universal solvent?

Because water is a highly polar molecule, it dissolves all polar and ionic substances.

What types of substances can be dissolved by water due to its high polarity?

All polar and ionic substances

Why does ice float on top of liquid water?

Because ice is less dense than water.

What ecological benefit does floating ice provide to aquatic life?

It enables fish to live in frozen ponds.

How much more acidic is a solution with a pH of $1$ compared to a solution with a pH of $2$?

It is $10$ times more acidic.

How much more acidic is a solution with a pH of $1$ compared to a solution with a pH of $3$?

It is $100$ times more acidic.

What is the definition of a buffer?

A special solution that stops major changes in pH levels when you add a small amount of acid or base.

What chemical solution concept is shown in this diagram?

Buffer

How do buffers act when excess hydrogen ions are added to a solution?

By absorbing excess hydrogen ions.

How do buffers act when hydrogen ions are too few in a solution?

By donating hydrogen ions.

What is the most important buffer found in human blood?

The bicarbonate ion ($\text{HCO}_3^-$).

What central element defines organic compounds?

Carbon

What are the four major classes of organic compounds?

Carbohydrates, lipids, proteins, and nucleic acids.

Which three elements make up carbohydrates?

Carbon, hydrogen, and oxygen

What are the two main types of simple carbohydrates?

Monosaccharides and disaccharides

What term refers to complex carbohydrates?

Polysaccharides

What is the general chemical formula for monosaccharides?

$$(\text{CH}_2\text{O})_n$$

How are monosaccharides categorized into three kinds?

According to the number of carbon atoms.

What is a triose, and what is its chemical formula?

A sugar with $3$ carbon atoms ($\text{C}_3\text{H}_6\text{O}_3$).

What triose is the first sugar molecule formed during photosynthesis?

G3P (glyceraldehyde 3 phosphate)

What is a pentose sugar?

A monosaccharide that has $5$ carbon atoms.

What is the chemical formula for ribose, and where is it important?

$\text{C}_5\text{H}_{10}\text{O}_5$; important in formation of ATP & RNA.

What is the chemical formula for deoxyribose, and where is it important?

$\text{C}_5\text{H}_{10}\text{O}_4$; important in formation of DNA.

Which pentose sugar is important in light independent reactions of photosynthesis?

Ribulose bi-phosphate

What is a hexose sugar, and what is its general formula?

A sugar with $6$ carbon atoms ($\text{C}_6\text{H}_{12}\text{O}_6$).

What is glucose commonly called, and what is its main function?

Grape sugar; primary cellular energy source for plants & animals.

What is fructose commonly called?

Fruit sugar

What is galactose commonly called?

Milk sugar

Why are glucose, fructose, and galactose classified as isomers?

Because they have the same molecular formula ($\text{C}_6\text{H}_{12}\text{O}_6$) but different structural formulas.

What is the definition of isomers?

Molecules that have the same molecular formula, but different structural formulas.

What structural pair of hexose sugars is shown in this figure?

Glucose and Fructose Structures

What is the general chemical formula for disaccharides?

$$\text{C}_{12}\text{H}_{22}\text{O}_{11}$$

What three disaccharides are listed in the study notes?

Lactose, maltose, and sucrose

By what process are two monosaccharides combined to form a disaccharide?

Dehydration synthesis

What summary table is represented in this image?

Dehydration Synthesis Table

What chemical process is the exact opposite of dehydration synthesis?

Hydrolysis

How is hydrolysis defined in the study notes?

Breakdown of a compound with the addition of water.

What products are created when sucrose undergoes hydrolysis?

Glucose and fructose

What chemical reaction equation represents the hydrolysis of sucrose?

$$\text{sucrose} + \text{water} \rightarrow \text{glucose} + \text{fructose}$$

What are polysaccharides?

Polymers of carbohydrates formed by many monosaccharides joined together by dehydration synthesis.

What primary direct function do carbohydrates serve for cell activities?

Direct source of energy for all cell activities.

How much heat energy is released when $1\,\text{gram}$ of carbohydrate is burned in a calorimeter?

$4\,\text{calories}$ of heat

Where is cellulose found in nature?

Plant cell walls

Where is chitin found in nature, and what is its function?

Structural function in arthropod exoskeletons and fungi cell walls.

What is starch?

Plant storage carbohydrate.

What is glycogen, and where is it stored in animals?

Animal starch stored in the liver and muscles.

Which elements compose lipids?

Carbon, hydrogen, oxygen, and sometimes phosphorus.

What four main types of lipids are specified in the study notes?

Fats and oils, phospholipids, cholesterol, and waxes

What is the structural composition common to both fats and oils?

Three fatty acids and one glycerol

What are the key traits of fats?

Animal-based, saturated, solid at room temperature, and cause heart diseases.

What are the key traits of oils?

Plant-based, unsaturated, and liquid at room temperature.

What type of lipid molecule is cholesterol?

Steroid (most important steroid)

In which type of cells is cholesterol uniquely found?

Animal cells only

Which sex hormones are constructed from cholesterol?

Estrogen, progesterone, and testosterone

How much energy is released when $1\,\text{gram}$ of lipid is burned?

$9\,\text{calories}$ of heat

Where are phospholipids functionally located in a cell?

In the cell membrane

What endocrine role do some lipids perform?

Functioning as hormones

What six functions of lipids are listed in the study notes?

Energy storage, structural (cell membrane), endocrine (hormones), cushioning organs, heat insulation, and buoyancy.

Which elements are present in proteins?

Carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur and phosphorus.

What monomers form proteins, and by what bonds are they linked?

Amino acids joined by peptide bonds

What defines the primary structure of a protein?

Sequence of amino acids linked by peptide bonds.

What shape and bond type characterize a protein's secondary structure?

Helical structure via hydrogen bonds.

What defines the tertiary structure of a protein?

3D shape, crucial for function and specificity.

What happens to a protein during denaturation?

Alters its 3D shape under high temperature or adverse pH.

Which environmental factors cause denaturation of a protein?

High temperature or adverse pH

What defines the quaternary structure of a protein?

Consisting of more than $1$ polypeptide chain.

What example of a protein with quaternary structure is given in the notes?

Hemoglobin

How many levels of structural organization do proteins have?

$4$ levels

What are enzymes?

Biological catalysts, large proteins of the tertiary type.

To which structural level of proteins do enzymes belong?

Tertiary type

How do enzymes speed up chemical reactions?

By lowering activation energy.

What is a substrate?

Substance the enzyme works on.

Which enzyme acts on proteins, and which acts on lipids?

Protease works on proteins; lipase works on lipids.

What does the induced-fit model describe?

Enzymes have specific active sites that fit specific substrates, altering shape slightly for a better fit.

What four factors affect enzyme efficiency?

pH, temperature, relative amounts of enzyme/substrate, and activators & inhibitors.

Which elements form nucleic acids?

Carbon, hydrogen, oxygen, nitrogen, and phosphorus.

What are nucleic acids composed of, and what is their function?

Polymers of nucleotides carrying hereditary information.

What basic structural unit of nucleic acids is depicted in this figure?

Nucleotide Structure

In what structural feature do all nucleotides differ from each other?

In their Nitrogenous Bases

Which structural components are identical across all nucleotides?

The sugar and phosphate

What are the four nitrogenous bases found in DNA?

Adenine, cytosine, guanine, and thymine

What are the four nitrogenous bases found in RNA?

Adenine, cytosine, guanine, and uracil (in place of thymine)