carbon and living things

phospholipids

Some lipids contain the element phosphorus as well as oxygen, carbon, and hydrogen. These lipids are called phospholipids. Two layers of phospholipid molecules make up most of the cell membrane in the cells of living things. Figure 9.22 shows how phospholipid molecules are arranged in a cell membrane. One end (the head) of each phospholipid molecule is polar and attracts water. This end is called hydrophilic ("water loving"). The other end (the tail) is nonpolar and repels water. This end is called hydrophobic ("water hating"). The nonpolar tails are on the inside of the membrane. The polar heads are on the outside of the membrane. These differences in polarity allow some molecules to pass through the membrane while keeping others out. You can see how this works in the video at the URL below.

structure of nucleic acids

Nucleic acids consist of chains of small molecules called nucleotides. The structure of a nucleotide is shown in Figure 9.23. Each nucleotide contains a phosphate group (PO4 ), a sugar (C5 H8 O4 ) in DNA, and a nitrogen- containing base. (A base is a compound that is not neither acidic nor neutral.) There are four different nitrogenous bases in DNA. They are adenine, thymine, guanine, and cytosine. In RNA, the only difference is that thymine is replaced with a different base, uracil. DNA consists of two long chains of nucleotides. Nitrogen bases on the two chains form hydrogen bonds with each other. Adenine always bonds with thymine, and guanine always bonds with cytosine. These bonds hold the two chains together and give DNA is characteristic double helix, or spiral, shape. You can see the shape of the DNA molecule in Figure 9.24. Sugars and phosphate groups form the "backbone" of each chain of DNA. The bonded bases are called base pairs. RNA, in contrast to DNA, consists of just one chain of nucleotides. Determining the structure of DNA was a big scientific breakthrough. You can read the interesting story of its discovery at the URL below.

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nucleic acids

Nucleic acids are biochemical molecules that contain oxygen, nitrogen, and phosphorus in addition to carbon and hydrogen. There are two main types of nucleic acids. They are DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).

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lipids

Lipids are biochemical compounds such as fats and oils. Organisms use lipids to store energy. In addition to carbon and hydrogen, lipids contain oxygen.

fatty acids

Lipids are made up of long carbon chains called fatty acids. Like hydrocarbons, fatty acids may be saturated or unsaturated. Figure 9.21 shows structural formulas for two small fatty acids. One is saturated and one is unsaturated. In saturated fatty acids, there are only single bonds between carbon atoms. As a result, the carbons are saturated with hydrogen atoms. Saturated fatty acids are found in fats. Fats are solid lipids that animals use to store energy. In unsaturated fatty acids, there is at least one double bond between carbon atoms. As a result, some carbons are not bonded to as many hydrogen atoms as possible. Unsaturated fatty acids are found in oils. Oils are liquid lipids that plants use to store energy.

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protein structure

Amino acids are the "building blocks" of proteins. There are 20 different common amino acids. The structural formula of the simplest amino acid, called glycine, is shown in Figure 9.19. Other amino acids have a similar structure. The sequence of amino acids and the number of amino acid chains in a protein determine the proteins shape. The shape of a protein, in turn, determines its function. Shapes may be very complex. You can learn more about the structure of proteins at the URL below. MEDIA Click image to the left or use the URL below. URL:

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protein functions

Proteins are the most common biochemicals. They have many different functions, including: making up tissues as components of muscle. speeding up biochemical reactions as enzymes. regulating life processes as hormones. helping defend against infections as antibodies. transporting materials as components of the blood (see the example in Figure 9.20).

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carbohydrates

Carbohydrates are biochemical compounds that include sugars, starches, and cellulose. They contain oxygen in addition to carbon and hydrogen. Organisms use carbohydrates mainly for energy.

biochemical compounds

A biochemical compound is any carbon-based compound found in living things. Like hydrocarbons, all biochemi- cal compounds contain hydrogen as well as carbon. However, biochemical compounds also contain other elements, such as oxygen and nitrogen. Almost all biochemical compounds are polymers. They consist of many, smaller monomer molecules. Biochemical polymers are referred to as macromolecules. The prefix macro means "large," and many biochemical molecules are very large indeed. They may contain thousands of monomer molecules. Biochemical compounds make up the cells and tissues of organisms. They are also involved in life processes, such as making and using food for energy. Given their diversity of functions, its not surprising that there are millions of different biochemical compounds. However, they can be grouped into just four main classes: carbohydrates, proteins, lipids, and nucleic acids. The classes are summarized in Table 9.3 and described in the rest of this lesson. Class Carbohydrates Elements carbon hydrogen oxygen Examples sugars starches cellulose Proteins carbon hydrogen oxygen nitrogen sulfur carbon hydrogen oxygen carbon hydrogen oxygen nitrogen phosphorus enzymes hormones Lipids Nucleic acids Functions provide energy to cells store energy in plants makes up the cell walls of plants speed up biochemical re- actions regulate life processes fats oils store energy in animals store energy in plants DNA RNA stores genetic information in cells helps cells make proteins

starches

Starches are complex carbohydrates. They are polymers of glucose. They consist of hundreds of glucose monomers bonded together. Plants make starch to store extra sugars. Consumers get starch from plants. Common sources of starch in the human diet are pictured in Figure 9.17. Our digestive system breaks down starch to simple sugars, which our cells use for energy.

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sugars

Sugars are simple carbohydrates. Molecules of sugar have just a few carbon atoms. The simplest sugar is glucose (C6 H12 O6 ). Glucose is the sugar that the cells of living things use for energy. Plants and some other organisms make glucose in the process of photosynthesis. Living things that cannot make glucose obtain it by consuming plants or these other organisms. You can see the structural formula of glucose and two other sugars in Figure 9.16. The other sugars in the figure are fructose and sucrose. Fructose is an isomer of glucose. It is found in fruits. It has the same atoms as glucose, but they are arranged differently. Sucrose is table sugar. It consists of one molecule of glucose and one molecule of fructose.

proteins

Proteins are biochemical compounds that contain oxygen, nitrogen, and sulfur in addition to carbon and hydrogen. Protein molecules consist of one or more chains of small molecules called amino acids.

cellulose

Cellulose is another complex carbohydrate that is a polymer of glucose. However, the glucose molecules are bonded together differently in cellulose than they are in starches. Cellulose molecules bundle together to form long, tough fibers (see Figure 9.18). Have you ever eaten raw celery? If you have, then you probably noticed that the stalks contain long, stringy fibers. The fibers are mostly cellulose. Cellulose is the most abundant biochemical compound. It makes up the cell walls of plants and gives support to trunks and stems. Cellulose also provides needed fiber in the human diet. We cant digest cellulose, but it helps keep food wastes moving through the digestive tract.

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functions of nucleic acids

DNA stores genetic information in the cells of all living things. It contains the genetic code. This is the code that instructs cells how to make proteins. The instructions are encoded in the sequence of nitrogen bases in the nucleotide chains of DNA. RNA "reads" the genetic code in DNA and is involved in the synthesis of proteins based on the code. This video shows how: (2:51). MEDIA Click image to the left or use the URL below. URL:

instructional diagrams

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questions

Classes of biochemical compounds include all of the following except

a. lipids.

b. proteins.

-->  c. phosphates.

d. nucleic acids.

Living things use lipids for

a. energy.

b. enzymes.

c. cell membranes.

-->  d. two of the above

Functions of proteins include

a. coding genetic information.

b. storing energy in animals.

-->  c. regulating life processes.

d. making up cell walls.

Which statement about RNA is true?

a. It has a double helix shape.

b. It consists of two chains of nucleotides.

-->  c. It is needed for the synthesis of proteins.

d. It contains the nitrogen base called thymine.

A nucleotide consists of a

a. phosphate group.

b. nitrogen base.

c. sugar.

-->  d. all of the above

All biochemical compounds contain hydrogen.

-->  a. true

b. false

There are a total of 20 different biochemical compounds.

a. true

-->  b. false

Some nucleic acids are hormones that regulate life processes.

a. true

-->  b. false

Biochemical compounds are carbon-based compounds found in living things.

-->  a. true

b. false

The simplest sugar is named sucrose.

a. true

-->  b. false

The main function of simple carbohydrates is to store energy in animals.

a. true

-->  b. false

Bread is a good source of starch in the diet.

-->  a. true

b. false

We need oils to help move food wastes through the digestive tract.

a. true

-->  b. false

The only biochemical compounds that contains sulfur are nucleic acids.

a. true

-->  b. false

Hemoglobin is a protein that fights infections in the blood.

a. true

-->  b. false

The most abundant biochemical compound is cellulose.

-->  a. true

b. false

Hemoglobin transports oxygen through the blood.

-->  a. true

b. false

Muscle tissues are composed mainly of fatty acids.

a. true

-->  b. false

Organisms use lipids mainly to store energy.

-->  a. true

b. false

There are two main types of nucleic acids.

-->  a. true

b. false

long carbon chains found in lipids

a. carbohydrates

b. lipids

c. proteins

d. nucleic acids

e. macromolecules

-->  f. fatty acids

g. amino acids

class of biochemical compounds that includes oils

a. carbohydrates

-->  b. lipids

c. proteins

d. nucleic acids

e. macromolecules

f. fatty acids

g. amino acids

general name given to biochemical polymers

a. carbohydrates

b. lipids

c. proteins

d. nucleic acids

-->  e. macromolecules

f. fatty acids

g. amino acids

class of biochemical compounds that includes DNA

a. carbohydrates

b. lipids

c. proteins

-->  d. nucleic acids

e. macromolecules

f. fatty acids

g. amino acids

building blocks of proteins

a. carbohydrates

b. lipids

c. proteins

d. nucleic acids

e. macromolecules

f. fatty acids

-->  g. amino acids

class of biochemical compounds that includes cellulose

-->  a. carbohydrates

b. lipids

c. proteins

d. nucleic acids

e. macromolecules

f. fatty acids

g. amino acids

class of biochemical compounds that includes enzymes

a. carbohydrates

b. lipids

-->  c. proteins

d. nucleic acids

e. macromolecules

f. fatty acids

g. amino acids

Which of the following is one of the four main classes of biochemical compounds?

a. sugars

b. starches

c. cellulose

-->  d. carbohydrates

All biochemical compounds include carbon, hydrogen, and

a. sulfur.

-->  b. oxygen.

c. nitrogen.

d. phosphorus.

Organisms use carbohydrates mainly for

-->  a. energy.

b. cell membranes.

c. hormones.

d. antibodies.

The function of a given protein depends on its

a. overall shape.

b. sequence of amino acids.

c. number of amino acid chains.

-->  d. all of the above

Which statement about saturated fatty acids is true?

-->  a. They have only single bonds between carbon atoms.

b. They are used by plants to store energy.

c. They make up lipids known as oils.

d. They are always in the liquid state.

Nitrogen bases found in both DNA and RNA include

a. glycine.

-->  b. adenine.

c. thymine.

d. uracil.

Which of the following is a function of RNA?

a. fighting infections

-->  b. reading the genetic code

c. carrying substances in the blood

d. all of the above

diagram questions

No diagram questions associated with this lesson