Ch1: Biochemistry

Question 1

Identify 4 functional groups and describe the properties of each. For each functional group give two examples of chemicals which the functional group can be found.

Answer 1

1.Hydroxyl Group (-OH):
◦Properties: It is polar and hydrophilic.
◦Examples: Alcohols (e.g., ethanol, glycerol) and sugars.

2.Carboxyl Group (-COOH):
◦Properties: It is polar, hydrophilic, and acts as a weak acid.
◦Examples: Carboxylic acids (e.g., acetic acid, fatty acid, amino acid) and sugars.

3.Amino Group (-NH2):
◦Properties: It is polar, hydrophilic, and acts as a weak base. It is found at the end of a molecule.
◦Examples: Amines (e.g., amino acids).

4.Phosphate Group (-PO4):
◦Properties: It is polar, hydrophilic, and acts as an acid. It can branch out.
◦Examples: Organic phosphates (e.g., DNA, ATP, phospholipids

Question 2

Compare and contrast dehydration synthesis and hydrolysis.

Answer 2

*Dehydration Synthesis (or Condensation Reaction): This is a chemical reaction that forms covalent bonds by removing a water molecule. Examples include:
◦The formation of glycosidic linkages between two simple sugars to create disaccharides.
◦The formation of peptide bonds that hold amino acids together to form polypeptides.
◦The formation of phosphodiester bonds that link nucleotides to form DNA or RNA strands.

*Hydrolysis: This is the process of breaking down a molecule by adding water. It is essentially the reverse of dehydration synthesis. An example is how enzymes in muscle and liver tissues hydrolyze glycogen into single glucose molecules for energy

Question 3

Many nutritionists recommend eating a low fat diet. Why do they not recommend a NO fat diet?

Answer 3

Nutritionists do not recommend a “no-fat” diet because fats (lipids) are essential molecules in living organisms. They serve several vital functions:

*Long-term energy storage: Fats are long-term energy-storing molecules.
*Insulation: Lipids are used for insulation.
*Organ cushioning: They provide cushioning for organs.
*Hormones and waxes: Lipids are also found in hormones and waxes.
*Cell membranes: Phospholipids, a type of lipid, are complex lipids that make up cell membranes.

Question 4

Which type of fat contains kinks in the fatty acid chain?How are these kinks created? What is the significance of these kinks?

Answer 4

Unsaturated fats contain kinks in their fatty acid chains.

These kinks are created due to the presence of double bonds between carbon atoms in the chain. In a cis-configuration, hydrogen atoms are on the same side of the double bond, which creates the bend or kink.

Significance: Kinks prevent tight packing, making the fat liquid at room temperature (e.g., oils) and more fluid in membranes.

Question 5

A fragment from a DNA strand has the following sequence: GATTAAC. WHat would the sequence be for the complementary strand?

Answer 5

CTAATTG

Question 6

Describe a lipid bilayer.

Answer 6

A lipid bilayer is a double layer of phospholipids that forms the basis of cell membranes. Each phospholipid molecule consists of a hydrophilic (water-loving) head and hydrophobic (water-fearing) tails.

When phospholipids are added to water, they form a bilayer where the hydrophilic heads face outwards towards the aqueous environment, and the hydrophobic tails mix in the center, forming a nonpolar core.

This structure is crucial because it makes the cell membrane selectively permeable, meaning water and other polar materials cannot easily pass through its nonpolar center.

Question 7

Describe the different ways materials can move across a membrane.

Answer 7

1.Passive Transport: Movement of molecules without energy input, driven by a concentration gradient.
◦Diffusion: Movement of molecules from an area of high concentration to low concentration until equilibrium is reached. Factors affecting diffusion include molecule size (small move easier), charge (neutral move easier), concentration gradient (steeper means faster), distance (shorter is faster), temperature (higher temp increases rate), and pressure (increased pressure forces molecules through). Diffusion is essential for bringing substances like oxygen into cells.
◦Osmosis: A type of diffusion specific to water molecules, moving from an area of high water concentration (low solute concentration) to low water concentration (high solute concentration).
◦Facilitated Diffusion: Diffusion that occurs through integral proteins (carrier proteins or channel proteins) embedded in the membrane. Carrier proteins bind to and transport specific molecules, while channel proteins allow ions to pass through. This method is used for larger and polarized molecules.

2.Active Transport: Transport of molecules against their concentration gradient, requiring energy in the form of ATP. This involves protein pumps (like the sodium-potassium pump) that change shape upon binding ions and ATP hydrolysis to move molecules across the membrane.

3.Membrane Assisted Transport (MAT): Used for transporting very large molecules and also requires energy.
◦Endocytosis: The process of taking in large materials by engulfing them into a vesicle.
▪Phagocytosis (“cell eating”): Occurs when the cell membrane or pseudopodium folds around large material and pinches off to form a vesicle. White blood cells use this to engulf and destroy viruses and bacteria.
▪Pinocytosis (“cell drinking”): Occurs when the cell membrane engulfs and pinches in to form a small vesicle, ingesting both fluid and small particles.

Question 8

What is the monomer of a carbohydrate?

Answer 8

Monosaccharide.

Monosaccharides are the simplest carbohydrates containing a single chain of carbon atoms with hydroxyl groups attached.

Question 9

What is the monomer of a nucleic acid?

Answer 9

Nucleotide.

A nucleotide subunit is composed of a 5-carbon (pentose) sugar, a nitrogenous base, and a phosphate group.

Question 10

What is the monomer of a protein?

Answer 10

Amino acid.

An amino acid is an organic molecule made up of an amino group, a central carbon atom, a carboxyl group, a hydrogen atom, and a side chain (R-group). There are 20 different amino acids.

Question 11

What are the main components of a cell membrane?

Answer 11

*Phospholipids: These form the basic bilayer structure.

*Proteins:
◦Integral proteins: Permanently embedded in the cell membrane (e.g., carrier proteins, channel proteins, aquaporins).
◦Peripheral proteins: Temporarily located on the surface of the membrane.

*Carbohydrates: Often attached to lipids or proteins on the membrane surface.
◦Glycoproteins: Carbohydrates attached to proteins, serving as markers or anchors.
◦Glycolipids: Carbohydrates attached to lipids, serving as recognition sites for cell communication.

**Cholesterol: Acts as a buffer between phospholipids, helping to maintain membrane fluidity and flexibility across different temperatures.

Question 12

What is the difference between a Glycoprotein and a Glycolipid?

Answer 12

Both glycoproteins and glycolipids are carbohydrates attached to components of the cell membrane, serving as recognition sites. The difference lies in what they are attached to:

*Glycoprotein: A carbohydrate attached to a protein. They function as markers or anchors.

*Glycolipid: A carbohydrate attached to a lipid. They serve as recognition sites for cell communication (e.g., immune responses, blood type, apoptosis) and tissue formation.

Question 13

Which of the following is NOT one of the six elements that form the chemical foundation of life?

a. Carbon
b. Nitrogen
c. Sulfur
d. Iron
e. Hydrogen

Answer 13

D

Question 14

What is the primary characteristic that distinguishes isotopes of an element?

a. Different number of protons
b. Different number of electrons
c. Different number of neutrons
d. Different atomic number
e. Different chemical properties

Answer 14

C

Question 15

What is the universal solvent?

Answer 15

Water

Question 16

Which functional group is characteristic of alcohols and is described as polar and hydrophilic?

a. Carbonyl (Ketones)
b. Carboxyl
c. Amino
d. Hydroxyl
e. Methyl

Answer 16

D

Question 17

Which of the following best describes a monomer?

a. A macromolecule consisting of many polymers.
b. A larger molecule formed from smaller units.
c. A single unit (molecule or atom) that can join together to form a larger molecule.
d. A protein folded into a specific 3D shape.
e. A complex lipid that makes up cell membranes.

Answer 17

C

Question 18

What is the main reason why monosaccharides with 5 or more carbons, like glucose, form ring structures when dissolved in water?

a. To increase their solubility in nonpolar solvents.
b. To expose their highly reactive carbonyl group.
c. To minimize the exposure of the highly reactive carbonyl group, increasing stability.
d. To form a glycosidic linkage with another monosaccharide.
e. To become isomers of each other.

Answer 18

C

Question 19

Disaccharides are formed when two simple sugars attach to one another by what type of covalent bond?

Answer 19

Glycosidic linkage

Question 20

Which of the following is a storage polysaccharide found in animals, primarily in muscle and liver cells?

a. Starch
b. Cellulose
c. Chitin
d. Glycogen
e. Amylose

Answer 20

D

Question 21

What configuration describes hydrogen atoms bound to opposite ends of the double bond in an unsaturated fatty acid, causing it to act more like a saturated fat?

a. Cis-configuration
b. Trans-configuration
c. Alpha-configuration
d. Beta-configuration
e. Ring configuration

Answer 21

B

Question 22

What are the key components of an amino acid?

a. A hydroxyl group, a phosphate group, and a fatty acid chain.
b. An amino group, a central carbon, a carboxyl group, a hydrogen atom, and a side chain R.
c. A 5-carbon sugar, a nitrogenous base, and a phosphate group.
d. A glycerol backbone and three fatty acid chains.
e. Two simple sugars attached by a covalent bond.

Answer 22

B

Question 23

How many different amino acids exist? Why?

Answer 23

20, 20 different R groups

Question 24

What best describes the property of the cell membrane that allows it to control what enters and exits the cell?

a. Hydrophilic
b. Nonpolar
c. Selectively permeable
d. Fluid mosaic
e. Rigid

Answer 24

D

Question 25

An increase in temperature affects the cell membrane by: a. Decreasing kinetic energy of phospholipids, making it less fluid. b. Increasing kinetic energy of phospholipids, making it more fluid. c. Causing phospholipids to pack more tightly. d. Decreasing the rate of diffusion across the membrane. e. Forcing the cell to become hypertonic.

Answer 25

B

Question 26

Which type of membrane transport moves molecules down a concentration gradient without energy input? a. Active transport b. Endocytosis c. Passive transport d. Exocytosis e. Membrane assisted transport

Answer 26

C

Question 27

What happens to a cell when it is placed in a hypertonic solution? a. Water will enter the cell, causing it to swell. b. Water will leave the cell, causing it to shrink. c. The cell will maintain its equilibrium and shape. d. Solutes will move into the cell against their concentration gradient. e. The cell will undergo phagocytosis.

Answer 27

B

Question 28

Which factor affecting diffusion indicates that a steeper concentration gradient leads to faster transportation of solute? a. Size b. Charge c. Distance d. Concentration gradient e. Temperature

Answer 28

D

Question 29

Which process is known as "cell eating," where the cell membrane folds around material and pinches off to form a vesicle? a. Pinocytosis b. Exocytosis c. Facilitated diffusion d. Phagocytosis e. Osmosis

Answer 29

D

Question 30

Why is the final shape of a polypeptide (protein structure) so critical to its function?

Answer 30

Because it directly relates to the protein's function. Proteins are diverse molecules, and their specific 3D shapes allow them to perform various roles, such as acting as enzymes (catalysts), forming structural components (like collagen), or transporting molecules (like hemoglobin). Any alteration to this specific shape can impair or destroy the protein's ability to function correctly.

Question 31

Explain the importance of DNA strands running antiparallel for the formation of hydrogen bonds between complementary base pairs.

Answer 31

For hydrogen bonds to form correctly between the complementary base pairs. This specific orientation ensures that the nitrogenous bases align properly for the formation of the specific hydrogen bonds (e.g., Adenine with Thymine, Guanine with Cytosine) that hold the two strands of the DNA double helix together.

Question 32

The cell membrane is described by the "Fluid Mosaic Model." What two main characteristics does this model emphasize about the cell membrane?

Answer 32

"Fluid" means it is not rigid; its components, particularly phospholipids, can switch spots constantly and even flip-flop, which maintains membrane fluidity and flexibility. "Mosaic" means it is composed of different molecules, not just phospholipids, but also integral proteins, peripheral proteins, glycoproteins, and glycolipids, which are embedded within or associated with the lipid bilayer

Question 33

Explain how cholesterol functions as a "buffer" within the cell membrane regarding temperature changes.

Answer 33

by helping to maintain optimal fluidity across temperature changes. When the temperature warms up, cholesterol holds the phospholipids together, preventing the membrane from becoming too fluid. Conversely, when the temperature cools down, cholesterol pushes the phospholipids apart, preventing the membrane from becoming too rigid and maintaining fluidity.

Question 34

Why are larger and polarized molecules often transported through integral proteins (carrier/channel proteins) instead of directly across the lipid bilayer?

Answer 34

The cell membrane's nonpolar interior, formed by the hydrophobic tails of the phospholipid bilayer, repels polar molecules. Therefore, larger and polarized molecules cannot easily pass directly through the lipid bilayer. Integral proteins, such as carrier proteins and channel proteins, provide specific pathways or pores through the

Question 35

Starch vs. Glycogen: Discuss their primary functions, where they are found, and in which organisms.

Answer 35

Similarities: Both are storage polysaccharides. Both are polymers of monosaccharides held together by glycosidic linkages. Differences: ▪Starch: Found in plants (mixture of amylose and amylopectin). Stores energy for plant growth and is abundant in seeds and roots. ▪Glycogen: Stored form of excess glucose molecules in animals. Found primarily in muscle and liver cells. Enzymes hydrolyze glycogen into glucose for energy.

Question 36

DNA vs. RNA: Discuss at least three key differences.

Answer 36

Similarities: Both are nucleic acids. Both are polymers of nucleotides and store genetic information. Both contain a phosphate group and a nitrogenous base. Differences: ▪DNA: Double-stranded. Contains deoxyribose sugar. Has nitrogenous bases Adenine, Guanine, Cytosine, and Thymine. ▪RNA: Single-stranded. Contains ribose sugar. Has nitrogenous bases Adenine, Guanine, Cytosine, and Uracil.

Question 37

Phagocytosis vs. Pinocytosis: Discuss the type of material ingested and the common name for each process.

Answer 37

Similarities: Both are forms of endocytosis, which is a type of membrane-assisted transport used for taking in large materials and requires energy. In both, the cell membrane engulfs material and pinches off to form a vesicle. Differences: ▪Phagocytosis: Known as "cell eating". Involves the engulfment of large solid materials, such as viruses or bacteria, by the cell membrane forming a vesicle. (e.g., white blood cells engulfing pathogens). ▪Pinocytosis: Known as "cell drinking". Involves the engulfment of fluid and small particles into small vesicles formed by the pinching in of the cell membrane.

Question 38

A patient is diagnosed with severe dehydration. Describe the tonicity of the patient's body cells relative to their extracellular fluid, and explain the net movement of water in this situation. What could be the visible effect on the cells?

Answer 38

If a patient is severely dehydrated, their body cells would be in a hypertonic solution relative to their extracellular fluid. This means the concentration of water outside the cells is lower than inside. As a result, there would be a net movement of water leaving the cells (osmosis) to try and achieve equilibrium. The visible effect on the cells would be that they shrink or crenate, as they lose water.

Question 39

A chef wants to make a dish that requires a fat that remains liquid at room temperature. Would they choose butter (an animal product) or olive oil (a plant product)? Justify your answer by explaining the typical fatty acid composition of each and its effect on physical state.

Answer 39

The chef should choose olive oil. Olive oil is a plant product, which typically contains a higher proportion of unsaturated fatty acids. Unsaturated fatty acids have carbon-carbon double bonds, which cause kinks in their hydrocarbon chains. These kinks prevent the fatty acid chains from packing tightly together, resulting in olive oil being liquid at room temperature. Butter, being an animal product, would primarily contain saturated fatty acids, which have straight chains, pack tightly, and are solid at room temperature.

Question 40

Compare and contrast: Proteins and Carbohydrates

Answer 40

Similarities: *Composition: organic macromolecules. They both primarily contain carbon, hydrogen, and oxygen atoms. *Polymer Structure *Bond Formation: Through dehydration/condensation reactions. *Energy Role: Both can serve as energy sources. Carbohydrates, especially monosaccharides, are quick and immediate sources of energy, and polysaccharides like starch and glycogen function as energy storage. Proteins, while primarily structural and functional, can also be used to yield energy. *Structural Role: Both biomolecules play important structural roles. Cellulose and chitin are structural polysaccharides in plants, insects, and fungi. Proteins like collagen are key structural components in living organisms. *Cellular Presence: Both are integral components within cells. Proteins are constructed in the cytoplasm and are found virtually everywhere in living organisms. Carbohydrates are common organic materials, produced by plants and algae. *Cell Membrane Involvement: Both play roles in the cell membrane. Proteins are embedded within the membrane (integral proteins) or located on its surface (peripheral proteins), serving functions like transport and recognition. Carbohydrates can be attached to proteins (glycoproteins) or lipids (glycolipids) on the cell surface, acting as recognition sites for cell communication. * Interaction with Water: Carbohydrates are hydrophilic and typically dissolve in water. Proteins are described as both hydrophobic and hydrophilic, indicating varying interactions with water depending on their specific composition and folding. Monosaccharides with five or more carbons form ring structures when dissolved in water, and proteins fold into specific 3D shapes. Differences: *Monomer and Bond Types: amino acids for proteins and monosaccharides (simple sugars) for carbohydrates. The bonds holding these monomers together also differ: peptide bonds for proteins and glycosidic linkages for carbohydrates. *Diversity and Primary Functions: Proteins are the most diverse molecules in living organisms, serving a vast array of functions including enzymatic catalysis, transport, structural support, and defense. Carbohydrates primarily serve as energy sources/storage and structural support. *Structural Complexity: Proteins exhibit four levels of structural organization (primary, secondary, tertiary, and quaternary), which dictate their final 3D shape and function. Carbohydrates, while forming complex polysaccharides, do not typically describe their structure in these four distinct hierarchical levels.