This document summarizes key concepts about carbohydrates, lipids, proteins, nucleic acids, and energy and living systems from Chapter 20. It discusses the structures and functions of monosaccharides, disaccharides, and polysaccharides. It also describes lipids, amino acids, proteins, enzymes, DNA, gene technology, photosynthesis, cellular respiration, and how ATP is used to do work in cells.

1. Chapter 20 QBA Miguel A. Castro R.
Carbohydrates and
Lipids

2. Carbohydrates and Living Systems
A monosaccharide (C6H12O6) is a simple sugar
that is the basic subunit of a carbohydrate.
A disaccharide (C12H22O11) is a sugar formed from
two monosaccharides.
Apolysaccharide is one of the carbohydrates
made up of long chains of simple sugars.

3. Carbohydrates and Living Systems
 Polysaccharides include starch, glycogen,
and cellulose.
 Potatoes have a lot of starch, the
polysaccharide that plants use for storing
energy.
 Many animals make use of a similar energy-
storage carbohydrate called glycogen.
 Cellulose is the polysaccharide that most
plants use to give their structures rigidity.

4. To a chemist, sugar is the name given to all
monosaccharides and disaccharides.

5. Each molecule of sucrose, the sugar used to
sweeten food, is made up of a glucose and a
fructose unit.

6. Carbohydrates
 Just as two monosaccharides combine
to form a disaccharide, many can
combine to form a long chain called a
polysaccharide.
 Polysaccharides may be represented
by the general formula below.
—O—(C6H10O4)—O—(C6H10O4)—O—(C6H10O4)...

7. Carbohydrates
 Polymerization is a series of synthesis
reactions that link many monomers
together to make a very large, chainlike
molecule.
 Polysaccharides and other large,
chainlike molecules found in living
things are called biological polymers.

10. Carbohydrate Reactions
 Polysaccharides are changed back to
sugars during hydrolysis reactions.
 In these reactions, the decomposition
of a biological polymer takes place
along with the breakdown of a water
molecule, as shown in the equation
below.

12. Lipids
A lipid is a type of biochemical that
does not dissolve in water, including
fats and steroids.
 Lipids
generally can have a polar,
hydrophilic region at one end of the
molecule. For example, oleic acid,
shown below is found in the fat of some
animals.

14. Lipids
 Lipids are used in animals for energy storage
as fats.
 Cell
membranes are made up of lipids called
phospholipids.
 Steroids, such as cholesterol, are lipids used
for chemical signaling.
 Waxes, such as those found in candles and
beeswax are also lipids.

16. Chapter 20
Proteins

17. Amino Acids and Proteins
A protein is a biological polymer that is
made up of nitrogen, carbon, hydrogen,
oxygen, and sometimes other elements.
 Our bodies are mostly made out of proteins.
 All proteins are biological polymers made up
of amino acid monomers.
 An amino acid is any one of 20 different
organic molecules that contain a carboxyl
and an amino group and that combine to
form proteins.

19. Amino Acids and Proteins
 Amino refers to the −NH2 group of
atoms.
 Acid
refers to the carboxylic acid group,
−COOH.
 Thereare 20 natural amino acids. All
20 have the same basic structure.

20. The R represents a side chain.

22. Amino Acids and Proteins
 Thereaction by which proteins are made
from amino acids is similar to the
condensation of carbohydrates.
 Thebiological polymer that forms during the
condensation of amino acids is called a
polypeptide.
 The link that joins the N and C atoms of two
different amino acids is called a peptide
bond.

26. Amino Acids and Proteins
 The sequence of amino acids—the primary
structure—helps dictate the protein’s final
shape.
A substitution of just one amino acid in the
polypeptide sequence can have major effects
on the final shape of the protein.
A hereditary blood cell disease called sickle
cell anemia gives one example of the
importance of amino-acid sequence.

28. Enzymes
 Anenzyme is a type of protein that
speeds up metabolic reactions in plant
and animals without being permanently
changed or destroyed.
 Almost all of the chemical reactions in
living systems take place with the help
of enzymes.

29. Enzymes
 Enzymes work like a lock and key. That is,
only an enzyme of a specific shape can fit
the reactants of the reaction that it is
catalyzing.
 Only a small part of the enzyme’s surface,
known as the active site, is believed to make
the enzyme active.
 In reactions that use an enzyme, the reactant
is called a substrate.

31. Chapter 20
Nucleic Acids

32. Information Storage
 Allhereditary information is stored
chemically in compounds called nucleic
acids.
 Nucleic acids are an organic
compound, either RNA or DNA, whose
molecules are made up of one or two
chains of nucleotides and carry genetic
information.

33. Nucleic-Acid Structure
• Like polysaccharides and
polypeptides, nucleic acids are
biological polymers. They are
made up of monomers called
nucleotides.

35. Information Storage
 The nucleic acid DNA, or deoxyribonucleic acid,
is the material that contains the information that
determines inherited characteristics.
 The sugar in DNA is deoxyribose, which has a
ring in which four of the atoms are carbon and
the fifth atom is oxygen.
 Deoxyriboseis connected to a phosphate group
and any one of four nitrogenous bases.

36. Information Strorage
 The nucleic acid DNA, or deoxyribonucleic
acid, is the material that contains the
information.
 The sugar in DNA is deoxyribose, which has
a ring in which four of the atoms are carbon
and the fifth atom is oxygen.
 Deoxyriboseis connected to a phosphate
group and any one of four nitrogenous
bases.

40. Information Storage
 Allgenetic information is encoded in
the sequence of the four bases, which
are abbreviated to A, G, T, and C.
 Justas history is written in books using
a 26-letter alphabet, heredity is written
in DNA using a 4-letter alphabet.

42. Gene Technology
 Because no one else has the same sequence of
DNA bases as you, your DNA pattern gives a unique
“fingerprint” of you.
 A DNA fingerprint is the pattern of bands that
results when an individual’s DNA sample is
fragmented, replicated, and separated.
 In DNA fingerprinting, scientists compare
autoradiographs, which are images that show the
DNA’s pattern of nitrogenous bases.

44. Gene Technology
 It takes a lot of DNA to make a DNA fingerprint, so
scientists must replicate DNA to get a large sample.
 Scientists use polymerase chain reaction, or PCR, to
replicate a sequence of double-stranded DNA.
 In PCR, scientists add DNA monomers, an enzyme,
and primers (short lengths of single-stranded DNA
with a specific sequence) to the sample of DNA.
 Heating and cooling repeatedly replicates the DNA.

46. Gene Technology
 Each cell of a very young embryo can grow into a
complete organism. These cells are undifferentiated.
 Undifferentiated cells have not yet specialized to
become part of a specific body tissue and include
stem cells in animals and meristem cells in plants.
 When they are cultured artificially they grow into
complete organisms, clones, that are genetically
identical to their “parent.”

48. Gene Technology
 Scientists can insert genes from one species into the
DNA of another.
 Recombinant DNA is DNA molecules that are
created by combining DNA from different sources
 When recombinant DNA is placed in a cell, the cell is
able to make the protein coded by the foreign gene.
 For example, recombinant DNA placed in bacteria
cells allow the bacteria to make human insulin.

49. Chapter 20
Energy and Living
Systems

50. Obtaining Energy
 Energy is needed for every action of every organ in
our bodies. All living things need energy.
 Plants get energy through photosynthesis, the
process by which they use sunlight, carbon dioxide,
and water to produce carbohydrates and oxygen.
 Other living things rely on plants for energy.
 The flow of energy throughout an ecosystem relates
to the carbon cycle, which follows carbon atoms as
they make up one compound and then another.

53. Obtaining Energy
 The carbon cycle involves two general reactions:
photosynthesis and respiration.
 The reactants needed for respiration—glucose and
oxygen—are produced in photosynthesis.
 The reactants needed for the photosynthesis—
carbon dioxide, water, and energy—are produced in
the respiration, although the energy is in a different
form.

55. Using Energy
 Glucose is changed into a more readily
available source of energy through
respiration.
 Inbiological chemistry, respiration is the
process by which cells produce energy from
carbohydrates.
 In respiration (also called cellular
respiration), oxygen combines with glucose
to form water and carbon dioxide.

56. • For every molecule of glucose that is broken down,
six molecules of O2 are consumed. Six molecules
of CO2 and six molecules of H2O are produced.

57. Using Energy
 While photosynthesis takes in energy, respiration
gives off energy.
 The thermodynamic values for the equation below
show that the reaction is very exothermic
(∆H = −1273 kJ)
 C6H12O6(aq) + 6O2(g) → 6CO2(g) + 6H2O(l)
 Respiration produces chemical energy (not heat
energy) in the form of special organic molecules.

58. Using Energy
 Adenosine triphosphate, ATP, an organic
molecule that acts as the main energy
source for cell processes.
 ATPis composed of a nitrogenous base, a
sugar, and three phosphate groups.
 Adenosine diphosphate, ADP, is the low-
energy forms of a ATP.

59. • The main structural difference between ATP and ADP
is that ATP has an extra phosphate group, −PO3−.

61. Using Energy
 There
are three kinds of work fueled by the
ATP → ADP conversion:
– Synthetic work involves making compounds that
do not form spontaneously.
– Mechanical work changes the shape of muscle
cells, which allows muscles to flex and move.
– Transport work involves carrying solutes across
a membrane.