Biology Chapter on Lipids and Proteins

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Questions and Answers

What is one primary function of chitin in arthropods?

Structural support in exoskeletons (correct)

Energy storage

Transport of nutrients

Facilitating cell division

Which of the following statements about lipids is correct?

They are primarily constructed from proteins.

They do not form polymers. (correct)

They are soluble in water.

They are hydrophilic molecules.

What component is essential in the structure of fats?

Fatty acids and amino acids

Steroids and phospholipids

Glycerol and fatty acids (correct)

Nucleic acids

How does chitin decompose in surgical applications?

It decomposes after the wound or incision heals. Signup and view all the answers

What characteristic makes lipids hydrophobic?

Presence of hydrocarbons and nonpolar covalent bonds Signup and view all the answers

What type of reaction is involved in the synthesis of a fat?

Dehydration reaction Signup and view all the answers

How are fats separated from water?

Through hydrogen bonding between water molecules Signup and view all the answers

What distinguishes saturated fatty acids from unsaturated fatty acids?

Saturated fatty acids have the maximum number of hydrogen atoms Signup and view all the answers

What is the common term for a molecule formed from one glycerol and three fatty acids?

Triacylglycerol Signup and view all the answers

What effect does a cis double bond have on the structure of fatty acids?

It causes bending in the fatty acid structure Signup and view all the answers

What is the structural arrangement of phospholipids when placed in water?

Hydrophilic heads pointing outward and hydrophobic tails inward Signup and view all the answers

Which statement about steroids is true?

Cholesterol is a type of steroid that is essential for animals Signup and view all the answers

Which of the following is NOT a function of proteins?

Regulating blood pressure Signup and view all the answers

What component of phospholipids interacts with water?

Hydrophilic head Signup and view all the answers

Why are phospholipids significant in cell membranes?

They form a bilayer that organizes cellular structure Signup and view all the answers

Which of the following describes a characteristic of cholesterol?

It stabilizes cell membranes in animals Signup and view all the answers

What is the primary composition of proteins in cells?

More than 50% of the dry mass of most cells Signup and view all the answers

Which of the following components is NOT found in phospholipids?

Nucleotides Signup and view all the answers

What is the primary function of normal hemoglobin as depicted in the structure?

To carry oxygen effectively Signup and view all the answers

What is the result of a hydrophobic region being exposed in sickle-cell hemoglobin?

Crystallization into fibers Signup and view all the answers

What happens to a protein when it undergoes denaturation?

It loses its biological activity Signup and view all the answers

Which of the following factors can influence protein structure?

Physical and chemical conditions Signup and view all the answers

What does the primary structure of hemoglobin refer to?

The sequence of amino acids in the polypeptide chain Signup and view all the answers

How does sickle-cell hemoglobin differ from normal hemoglobin in terms of structure?

It forms a fiber under low oxygen conditions Signup and view all the answers

What typically results if a protein is subjected to extreme changes in environmental conditions?

It might undergo denaturation Signup and view all the answers

What characteristic of sickle-cell hemoglobin contributes to reduced oxygen-carrying capacity?

Crystallization into a fiber form Signup and view all the answers

What role does insulin play in the body?

Regulates blood sugar concentration Signup and view all the answers

Which proteins are primarily responsible for muscle contraction?

Actin and myosin Signup and view all the answers

What is the function of storage proteins?

Store amino acids Signup and view all the answers

What type of protein is responsible for coordinating an organism's activities?

Hormonal proteins Signup and view all the answers

Which example is NOT a function of enzymatic proteins?

Inactivating viruses Signup and view all the answers

What characteristic is NOT associated with hormonal proteins?

Directly contracting muscles Signup and view all the answers

Which statement about defensive proteins is true?

They help inactivating viruses and bacteria. Signup and view all the answers

What role do collagen and elastin play in the body?

Providing structural support in connective tissues Signup and view all the answers

Which of the following describes a purine?

A nitrogenous base with a six-membered ring fused to a five-membered ring Signup and view all the answers

What sugars are found in DNA and RNA respectively?

Deoxyribose in DNA, ribose in RNA Signup and view all the answers

How is a nucleotide defined?

A nucleoside and a phosphate group Signup and view all the answers

Which of the following nitrogenous bases is NOT a pyrimidine?

Adenine Signup and view all the answers

What is the structure of pyrimidines?

A single six-membered ring Signup and view all the answers

Where does the phosphate group attach in a nucleotide?

At the 5' position of the sugar Signup and view all the answers

What component is absent in RNA compared to DNA?

Thymine Signup and view all the answers

What is a nucleoside composed of?

Nitrogenous base and sugar Signup and view all the answers

Which nitrogenous base is found only in RNA?

Uracil Signup and view all the answers

What role does the sugar-phosphate backbone play in nucleic acids?

It serves as a structural support Signup and view all the answers

Study Notes

Lecture Presentations

Chapter 5: The Structure and Function of Large Biological Molecules
Lectures by Erin Barley and Kathleen Fitzpatrick

Overview: The Molecules of Life

All living things are made up of four classes of large biological molecules: carbohydrates, lipids, proteins, and nucleic acids
Macromolecules are large molecules composed of thousands of covalently connected atoms
Molecular structure and function are inseparable

Concept 5.1: Macromolecules are Polymers, Built from Monomers

A polymer is a long molecule consisting of many similar building blocks
These small building block molecules are called monomers
Three of the four classes of life's organic molecules are polymers: carbohydrates, proteins, and nucleic acids

The Synthesis and Breakdown of Polymers

A dehydration reaction occurs when two monomers bond together through the loss of a water molecule
Polymers are disassembled to monomers by hydrolysis, a reaction that is essentially the reverse of the dehydration reaction

The Diversity of Polymers

Each cell has thousands of different macromolecules
Macromolecules vary among cells of an organism, vary more within a species, and vary even more between species
An immense variety of polymers can be built from a small set of monomers

Concept 5.2: Carbohydrates Serve as Fuel and Building Material

Carbohydrates include sugars and the polymers of sugars
The simplest carbohydrates are monosaccharides, or single sugars
Carbohydrate macromolecules are polysaccharides, polymers composed of many sugar building blocks

Sugars

Monosaccharides have molecular formulas that are usually multiples of CH₂O
Glucose (C₆H₁₂O₆) is the most common monosaccharide
Monosaccharides are classified by the location of the carbonyl group (as aldose or ketose) and the number of carbons in the carbon skeleton

Figure 5.3

Aldoses (aldehyde sugars) and ketoses (ketone sugars) are shown
Trioses (3-carbon sugars), pentoses (5-carbon sugars), and hexoses (6-carbon sugars) are shown
Structures of various sugars (e.g., glucose, galactose, fructose, ribose, ribulose) are included

Figure 5.4

Linear and ring forms of monosaccharides are shown
Abbreviated ring structure of monosaccharides are shown

Disaccharides

A disaccharide is formed when a dehydration reaction joins two monosaccharides
This covalent bond is called a glycosidic linkage

Polysaccharides

Polysaccharides, the polymers of sugars, have storage and structural roles
The structure and function of a polysaccharide are determined by its sugar monomers and the positions of glycosidic linkages

Storage Polysaccharides

Starch, a storage polysaccharide of plants, consists entirely of glucose monomers
Plants store surplus starch as granules within chloroplasts and other plastids
The simplest form of starch is amylose
Glycogen, a storage polysaccharide in animals, is mainly stored in liver and muscle cells

Structural Polysaccharides

The polysaccharide cellulose is a major component of the tough wall of plant cells
Like starch, cellulose is a polymer of glucose, but the glycosidic linkages differ
The difference is based on two ring forms for glucose: alpha (α) and beta (β)
Polymers with α glucose are helical, and polymers with β glucose are straight
Parallel cellulose molecules held together this way are grouped into microfibrils, which form strong building materials for plants

Chitin

Chitin, another structural polysaccharide, is found in the exoskeleton of arthropods
Chitin also provides structural support for the cell walls of many fungi

Concept 5.3: Lipids are a Diverse Group of Hydrophobic Molecules

Lipids are the one class of large biological molecules that do not form polymers
The unifying feature of lipids is having little or no affinity for water
Lipids are hydrophobic because they consist mostly of hydrocarbons, which form nonpolar covalent bonds
The most biologically important lipids are fats, phospholipids, and steroids

Fats

Fats are constructed from two types of smaller molecules: glycerol and fatty acids
Glycerol is a three-carbon alcohol with a hydroxyl group attached to each carbon
A fatty acid consists of a carboxyl group attached to a long carbon skeleton

Figure 5.10

One of three dehydration reactions in the synthesis of a fat is shown
A fat molecule (triacylglycerol) is shown

Fats (continued)

Fats separate from water because water molecules form hydrogen bonds with each other and exclude the fats
In a fat, three fatty acids are joined to glycerol by an ester linkage, creating a triacylglycerol, or triglyceride

Fatty Acids

Fatty acids vary in length (number of carbons) and in the number and locations of double bonds
Saturated fatty acids have the maximum number of hydrogen atoms possible and no double bonds
Unsaturated fatty acids have one or more double bonds
Fats made from saturated fatty acids are called saturated fats, and are solid at room temperature
Most animal fats are saturated
Fats made from unsaturated fatty acids are called unsaturated fats or oils, and are liquid at room temperature
Plant fats and fish fats are usually unsaturated

Hydrogenation

A diet rich in saturated fats may contribute to cardiovascular disease through plaque deposits
Hydrogenation is the process of converting unsaturated fats to saturated fats by adding hydrogen
Hydrogenating vegetable oils also creates unsaturated fats with trans double bonds
These trans fats may contribute more than saturated fats to cardiovascular disease

Essential Fatty Acids

Certain unsaturated fatty acids are not synthesized in the human body
These must be supplied in the diet

Functions of Fats

The major function of fats is energy storage
Humans and other mammals store their fat in adipose cells
Adipose tissue also cushions vital organs and insulates the body

Phospholipids

In a phospholipid, two fatty acids and a phosphate group are attached to glycerol
The two fatty acid tails are hydrophobic, but the phosphate group and its attachments form a hydrophilic head

Figure 5.12

Structural formula of a phospholipid is shown
Space-filling model of a phospholipid is shown
Phospholipid symbol is shown
When phospholipids are added to water, they self-assemble into a bilayer, with the hydrophobic tails pointing toward the interior
The structure of phospholipids results in a bilayer arrangement found in cell membranes
Phospholipids are the major component of all cell membranes

Steroids

Steroids are lipids characterized by a carbon skeleton consisting of four fused rings
Cholesterol, an important steroid, is a component in animal cell membranes

Figure 5.14

Structure of cholesterol is shown

Concept 5.4: Proteins Include a Diversity of Structures, Resulting in a Wide Range of Functions

Proteins account for more than 50% of the dry mass of most cells
Protein functions include structural support, storage, transport, cellular communications, movement, and defense against foreign substances

Figure 5.15a

Enzymatic, defensive, storage, and transport proteins are described
Examples for each class are also given

Figure 5.15b

Hormonal, receptor, contractile and motor, and structural proteins are described
Examples for each class are also given

Enzymes

Enzymes are a type of protein that acts as a catalyst to speed up chemical reactions
Enzymes can perform their functions repeatedly, functioning as workhorses that carry out the processes of life

Polypeptides

Polypeptides are unbranched polymers built from the same set of 20 amino acids
A protein is a biologically functional molecule that consists of one or more polypeptides

Amino Acids

Amino acids are organic molecules with carboxyl and amino groups
Amino acids differ in their properties due to differing side chains, called R groups

Figure 5.16

Nonpolar, polar, and electrically charged side chains (R groups) of amino acids are shown
The structure of some of the 20 amino acids and their properties are shown

Amino Acid Polymers

Amino acids are linked by peptide bonds
A polypeptide is a polymer of amino acids
Polypeptides range in length from a few to more than a thousand monomers

Figure 5.17

Peptide bond formation between two amino acids, with the loss of a water molecule, is illustrated
The polypeptide backbone is shown with an amino end (N-terminus) and a carboxyl end (C-terminus).

Protein Structure and Function

A functional protein consists of one or more polypeptides precisely twisted, folded, and coiled into a unique shape

Figure 5.18

Ribbon and space-filling models of a protein are shown

Protein Structure (Key Points)

The sequence of amino acids determines a protein's three-dimensional structure
A protein's structure determines its function

Figure 5.19

Ribbon models of an antibody protein and a protein from a flu virus are shown

Four Levels of Protein Structure

The primary structure of a protein is its unique sequence of amino acids
Secondary structure, found in most proteins, consists of coils and folds in the polypeptide chain
Tertiary structure is determined by interactions among various side chains (R groups)
Quaternary structure results when a protein consists of multiple polypeptide chains

Sickle-Cell Disease

A slight change in primary structure can affect a protein's structure and ability to function
Sickle-cell disease, an inherited blood disorder, results from a single amino acid substitution in the protein hemoglobin

Figure 5.21

Primary, secondary and tertiary structure of normal and sickle-cell hemoglobin are compared
The effect on red blood cell shape is shown

What Determines Protein Structure?

In addition to primary structure, physical and chemical conditions can affect structure
Alterations in pH, salt concentration, temperature, or other environmental factors can cause a protein to unravel
This loss of a protein's native structure is called denaturation

Figure 5.22

Normal and denatured protein shapes are shown schematically

Protein Folding in the Cell

It is hard to predict a protein's structure from its primary structure
Most proteins probably go through several stages on their way to a stable structure
Chaperonins are protein molecules that assist the proper folding of other proteins
Diseases such as Alzheimer's, Parkinson's, and mad cow disease are associated with misfolded proteins

Figure 5.23

Steps of chaperonin action are illustrated

Determining Protein Structure

Scientists use X-ray crystallography to determine a protein's structure
Another method is nuclear magnetic resonance (NMR) spectroscopy, and does not require protein crystallization
Bioinformatics uses computer programs to predict protein structure from amino acid sequences

Figure 5.24

X-ray crystallography experiment outline is given
Results showing a protein structure based on X-ray crystallography is shown

Concept 5.5: Nucleic Acids Store, Transmit, and Help Express Hereditary Information

The amino acid sequence of a polypeptide is programmed by a unit of inheritance called a gene
Genes are made of DNA, a nucleic acid made of monomers called nucleotides

The Roles of Nucleic Acids

Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are two types of nucleic acids
DNA provides directions for its own replication
DNA directs synthesis of messenger RNA (mRNA) and, through mRNA, controls protein synthesis
Protein synthesis occurs on ribosomes

Figure 5.25-1, Figure 5.25-2, Figure 5.25-3

A schematic diagram of the flow of information from DNA to RNA to protein synthesis is shown.

The Components of Nucleic Acids

Nucleic acids are polymers called polynucleotides
Each polynucleotide is made of monomers called nucleotides
Each nucleotide consists of a nitrogenous base, a pentose sugar, and one or more phosphate groups
The portion of a nucleotide without the phosphate group is called a nucleoside

Figure 5.26

Sugar-phosphate backbone of a polynucleotide is illustrated
Nitrogenous bases and sugars are shown

Nucleotide (continued)

Nucleoside = nitrogenous base + sugar
There are two families of nitrogenous bases: pyrimidines and purines
In DNA, the sugar is deoxyribose; in RNA, the sugar is ribose
Nucleotide = nucleoside + phosphate group

Nucleotide Polymers

Nucleotide polymers are linked together to build a polynucleotide
Adjacent nucleotides are joined by covalent bonds that form between the -OH group on the 3' carbon of one nucleotide and the phosphate on the 5' carbon on the next
These links create a backbone of sugar-phosphate units with nitrogenous bases as appendages
The sequence of bases along a DNA or mRNA polymer is unique for each gene

DNA and RNA Structures

RNA molecules usually exist as single polypeptide chains
DNA molecules have two polynucleotides spiraling around an imaginary axis, forming a double helix
In the DNA double helix, the two backbones run in opposite 5'→ 3' directions from each other, an arrangement referred to as antiparallel
One DNA molecule includes many genes

Complementary Base Pairing

The nitrogenous bases in DNA pair up and form hydrogen bonds: adenine (A) always with thymine (T), and guanine (G) always with cytosine (C)
Complementary pairing can also occur between two RNA molecules or between parts of the same molecule
In RNA, thymine is replaced by uracil so A and U pair

Figure 5.27

DNA and transferencia RNA (tRNA) structures showing complementary base pairing are illustrated

DNA and Proteins as Tape Measures of Evolution

The linear sequences of nucleotides in DNA molecules are passed from parents to offspring
Two closely related species are more similar in DNA than are more distantly related species
Molecular biology can be used to assess evolutionary kinship

The Theme of Emergent Properties in the Chemistry of Life: A Review

Higher levels of organization result in the emergence of new properties
Organization is the key to the chemistry of life

Figure 5.UN02, Figure 5.UN02a, Figure 5.UN02b

Summary table of large biological molecules, their components, examples, and functions

Figures 5. UN03, 5. UN04, 5. UN05, 5. UN06, 5. UN07, 5. UN08, 5. UN09, 5. UN10, 5. UN11, 5.UN12, 5. UN13

Various diagrams of molecular structures and processes.

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Description

Test your knowledge on the structure and function of lipids and proteins in biological systems. This quiz covers essential concepts related to fatty acids, phospholipids, and the role of chitin in arthropods, as well as the characteristics and functions of these crucial biomolecules.