Thursday, August 28, 2008

Chapter 3 Practice Quiz Questions & Ch. 2/3 Homework Answers

MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.

1) A molecule inside a cell consists of over 3,500 covalently linked atoms weighing about 105,000 daltons. From this description, the molecule can most specifically be described as a
A) macromolecule.
B) polysaccharide.
C) lipid.
D) polypeptide.
E) protein.

2) Polymers of polysaccharides, fats, and proteins are all synthesized from monomers by
A) connecting monosaccharides together.
B) the formation of disulfide bridges between monomers.
C) ionic bonding of the monomers.
D) the addition of water to each monomer.
E) the removal of water (dehydration reactions).

3) Which of the following best summarizes the relationship between dehydration reactions and hydrolysis?
A) Dehydration reactions occur in plants, and hydrolysis happens in animals.
B) Hydrolysis occurs during the day, and dehydration reactions happen at night.
C) Hydrolysis creates monomers, and dehydration reactions destroy them.
D) Dehydration reactions assemble polymers, and hydrolysis breaks them down.
E) Dehydration reactions can occur only after hydrolysis.

4) Carbohydrates normally function in animals as
A) energy-storage molecules.
B) the functional units of lipids.
C) sites of protein synthesis.
D) enzymes in the regulation of metabolic processes.
E) a component of triglycerides.

5) The 20 different amino acids found in polypeptides exhibit different chemical and physical properties because of different
A) amino groups.
B) side chains (R groups).
C) tertiary structure.
D) carboxyl groups.
E) Both A and B are correct.

6) The bonding of two amino acid molecules to form a larger molecule requires the
A) addition of a nitrogen atom.
B) release of a water molecule.
C) addition of a water molecule.
D) release of a carbon dioxide molecule.
E) Both C and D are correct.

7) Which bonds are created during the formation of the primary structure of a protein?
A) peptide bonds
B) hydrogen bonds
C) disulfide bonds
D) Only A and C are correct.
E) A, B, and C are correct.

8) How many different kinds of polypeptides, each composed of 5 amino acids, could be synthesized using the 20 common amino acids?
A) 5 B) 20 to power of (10) C) 5 to power of (5) D) 20 to power of (5) E) 20

9) Consider a polysaccharide consisting of 828 glucose molecules. The total hydrolysis of the polysaccharide would result in the production of
A) 828 glucose molecules and 828 water molecules.
B) 827 glucose molecules.
C) 828 glucose molecules and no water molecules.
D) 827 water molecules.
E) 827 glucose molecules and 827 water molecules.

10) Which of the following are polysaccharides?
A) glycogen and starch
B) glucose and sucrose
C) uracil and thymine
D) RNA and DNA
E) cholesterol and triacylglycerol

11) Which of the following is true of both starch and cellulose?
A) They can both be digested by humans.
B) They are both structural components of the plant cell wall.
C) They are geometric isomers of each other.
D) They are both polymers of glucose.
E) They are both used for energy storage in plants.

12) What is a fat or triacylglycerol?
A) a lipid made of three fatty acids and glycerol
B) a molecule formed from three alcohols
C) a carbohydrate with three sugars
D) a protein with tertiary structure
E) a kind of lipid that makes up much of the plasma membrane

13) Which of the following is true concerning saturated fatty acids?
A) They are the predominant fatty acid in corn oil.
B) They have double bonds between the carbon atoms of the fatty acids.
C) They are usually liquid at room temperature.
D) They are usually produced by plants.
E) They have a higher ratio of hydrogen to carbon than do unsaturated fatty acids.

14) The hydrogenation of vegetable oil would result in
A) an increase in the number of hydrogen atoms in the oil molecule.
B) a decrease in the number of carbon-carbon double bonds in the oil molecules.
C) the oil being a solid at room temperature.
D) two of the above.
E) all of the above.

15) Which type of lipid is most important in biological membranes?
A) fat B) oil C) wax D) triglyceride E) phospholipid

1) Answer: A 2) Answer: E 3) Answer: D 4) Answer: A 5) Answer: B 6) Answer: B 7) Answer: A 8) Answer: D 9) Answer: C 10) Answer: A 11) Answer: D 12) Answer: A 13) Answer: E 14) Answer: E15) Answer: E

Chapter 2 Notebook Questions

1. How are protons, electrons, and neutrons arranged into atoms and ions.

Protons, neutrons, and electrons are the subatomic particles of atoms.

Protons carry a positive charge and they are located in the nucleus.
Neutrons carry no charge.
Electrons carry a negative charge and move around the nucleus.

When the number of protons and electrons equal other the element is said to be neutral.

If the element has more protons than electrons it becomes positive.
If the element has more electrons than protons it becomes negative.

Charged elements are called ions.

2. What are the properties of isotopes and how can these properties be useful to researchers.

Isotopes are atoms of an element that differ in the number of neutrons they contain.

Some are radioactive and unstable.

Some isotopes undergo radioactive decay and are considered radioisotopes.

3. Explain how the distribution of electrons in an atom or ion determines the number and kinds of chemical bonds that can be formed.

Ionic bonding can result when one element gives up an electron to become more stable and another ion accepts the electron to become more stable.

Covalent bonding can result when two elements share electrons to become more stable.

Hydrogen bonds form between a hydrogen and another molecule because hydrogen wants to accept or share one more electron. These bonds are very weak and break easily.
4. Know the various types of chemical bonds, the circumstances under which each forms, and the relative strengths of each type.

Covalent bonds are the strongest of the three bonds. When atoms share two electrons or more they are a covalent bond.

Ionic bonds are stronger than ionic bonds. When atoms give up electrons or accept electrons they are ionically bonded together.

Hydrogen bonds are the weakest and can easily break and form. They form between a hydrogen atom and a negatively charged atom in a different molecule.

5. What are some common substances that dissolve in water.

Water can dissolve ionic substances and molecules that have a charge – salt, anything that is a polar covalent bond. It does not dissolve oil because oil is nonpolar. Remember likes dissolve likes.

6. Discuss the unique properties of water that make it vital to living organisms.

• Water has temperature stabilizing effects. Our cells are mostly made up of water. They generate a lot of heat through metabolic processes. Because the hydrogen bonds are constantly moving in water molecules it is very hard to raise the temperature of water. This prevents the cells from boiling.
• Water is an excellent solvent. Water dissolves substances in your blood stream and gut all the time.
• Cohesion is a resistance to being stretched. This creates high surface tension which is observed when you throw a pebble on a lake. This property allows plants to pull water from the ground.

7. What is the relationship between acids, bases, and salts. Compare and contrast their properties.

• Acids donate hydrogen bonds.
• Bases accept hydrogen bonds.
• A salt is any substance that dissolves easily in water and releases ions other than hydrogen and hydroxide.

Chapter 3:

1. How can small organic molecules be assembled into large macromolecules by condensation? Describe how large macromolecules can be broken into subunits by hydrolysis.

A condensation reaction is responsible for building large molecules. An enzyme catalyzes the reaction between alcohol groups on adjacent monomer units (eg. glucose). This results in the production of a polymer and a molecule of water.

A hydrolysis reaction is responsible for breaking down large molecules (eg. digestion). An enzyme weakens the bond between two parts of a polymer, allowing for the insertion of a water molecule into the bond. This results in the production of monomers.

2. Name five functional groups and describe how they can change the property of a molecule when attached to it.

• Hydroxyl – OH – in alcohols – water soluble
• Methyl – CH3 – insoluble in water
• Carbonyl – CO (Ketone) – water soluble
• Amino – NH2 – water soluble – acts as a weak base
• Phosphate – P – water soluble – acidic
• Sulfhydryl – SH – helps stabilize protein structure

3. Describe the general structure of a monosaccharide, a fatty acid, an amino acid, and a nucleotide.

• Monosaccharides – simplest carbohydrate – one sugar unit – 2 OH groups bonded to their carbon backbone and one aldehyde or ketone group. – 5 or 6 carbon atoms that tend to form rings when dissolved in water.
• Fatty Acid – start as a carboxyl group attached to a backbone of as many as 36 carbon atoms. Each carbon in the backbone has one, two, or three hydrogen atoms covalently bonded to it.
• Amino Acid – small organic compound with an amino group – NH3, a carboxyl group COO, a hydrogen atom, and one or more atoms called its R group.
• Nucleotide – have one sugar, at least one phosphate group, and one nitrogen containing base. The sugar is deoxyribose or ribose.

4. Describe the monosaccharides – give an example of three and how cells use these molecules.

• Ribose used in RNA – 5 carbon atoms
• Deoxyribose used in DNA – 5 carbon atoms
• Glucose – 6 carbon atoms – an instant energy source.

5. What is an oligosaccharide and what is their function?

• Oligosaccharide is a short chain of covalently bonded sugar monomers.
• Proteins and lipids have oligosaccharide side chains which serve as flags and docks at the cell surface for identification.
• Common oligosaccharides include: lactose and sucrose.

6. What is a disaccharide (describe its structure) and give 2 examples of this molecule and describe how they are used in the body.

• Disaccharide consist of two sugar monomers and two examples are lactose found in milk and sucrose the most plentiful sugar in nature.

7. Describe the structure of a polysaccharide and name and describe four types found in cells and give their function.

• Polysaccharides are straight or branched chains of many sugar monomers – hundreds or thousands.
• Starch is a polysaccharide and is how plants store glucose
• Cellulose is tough, insoluble, and resistant to weight loads and mechanical stress.
• Glycogen is the sugar storage equivalent of starch. Muscle and liver cells store a lot of it.
• Chitin strengthens the external skeleton and other hard parts of many animals, including crabs, earthworms, insects, spiders, and ticks.

8. Describe the structure of the lipid and describe the difference between saturated and unsaturated fatty acids. Describe three important lipids used in cells and describe their function.

• Lipids are fats which are made up of one, two, or three fatty acids dangling like tails from a glycerol molecule. It starts as a carboxyl group attached to a backbone of as many as 36 carbon atoms. Each carbon in the backbone has as many as 1, 2, or 3 hydrogen atoms covalently bonded to it.
• Phospholipids make up the cell membrane and make it semi permeable.
• Waxes have a firm consistency and repel water. Surfaces of plants have a cuticle that contains water. Waxes protect, lubricate, and lend pliability to hair and skin. Birds secrete waxes, fats, and fatty acids that waterproof feathers. Bees use honeywax for honeycomb, which houses new generations of bees as well as honey.

9. Describe the structure and function of proteins. Describe the difference in structure between the primary, secondary, tertiary, and quaternary structure.

• A protein is made of a chain of amino acids strung together and is held together by peptide bonds.
• A proteins primary structure is a sequence of covalently bonded amino acids that make up a polypeptide chain.
• The secondary structure results from chains being twisted into helical coils, sheetlike arrays, and loops.
• The tertiary structure results when the shape of the protein becomes structurally stable.
• The quaternary structure consists of two or more polypeptide chains associating with each other.

10. Explain why protein structure is so important. Describe how sickle cell anemia occurs.

Proteins can not function unless they stay coiled, packed, folded in a precise way.

Hemoglobin is responsible for carrying oxygen throughout the body. A hemoglobin molecule is made up of four tightly packed globins.

Each globin chain is folded into a pocket that cradles a heme group – a large organic molecule with an iron atom at the center. Heme carries oxygen.

Globin has two forms – alpha and beta. Two of each form make up the hemoglobin in humans.

In a beta chain glutamate is the sixth amino acid.

A DNA mutation sometimes inserts valine in this position instead.

Glutamate has a negative charge whereas valine is neutral.

One small patch of protein changes its polarity (polar to nonpolar).

Each person inherits two genes for beta globin – one from each parent.

If one is normal and one abnormal the person can lead a normal life.

However, if a person inherits two mutant genes – sickle cell anemia results.

Normally as hemoglobin returns to the lungs to pick up more oxygen hemoglobin will clump together. However, the mutant molecules do not form clusters – instead they form large rod shaped aggregates which are sickle shaped. These clog tiny vessels and disrupt blood circulation. Tissues become oxygen starved.

11. What is the difference between DNA and RNA?

DNA consists of two nucleotide strands joined by hydrogen bonds and twisted as a double helix. Contains Deoxyribose – can not leave the nucleus.

RNA is a single stranded nucleic acid. RNA can leave the nucleus, RNA has ribose.

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