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ABCT 1101/ABCT1D04
Introductory Life Science

INTRODUCTORY LIFE SCIENCE
At our 3rd lecture, we want to discuss

• The building blocks of biological organisms
– Carbohydrates, proteins, lipids and nucleic acids

• Cell structure and function
– Cell membrane, ER, Golgi, cytoskeleton, nucleus
– Plant cell vs. animal cell

Simple Chemistry for Life Science
• Each element consists of one kind of atom.
– An atom is the smallest unit of matter that still retains the properties of an element.

– An atom contains subatomic particles including proton, neutron, and electrons.

2

Protons
Nucleus

2
2
Nucleus

Neutrons
Electrons

2e–
Electron cloud

Simple Chemistry for Life Science
• Atomic structure of the 4 common elements.
– The number of electrons in the outermost shell determines the chemical properties of an atom
Electron

First electron shell
(can hold 2 electrons)

Hydrogen (H)
Atomic number  1

Outer electron shell
(can hold 8 electrons)

Carbon (C)
Atomic number  6

Nitrogen (N)
Atomic number  7

Oxygen (O)
Atomic number  8

Simple Chemistry for Life Science
• Chemical reactions enable atoms to give up or acquire electrons, completing their outer shells.
• Chemical reactions usually result in atoms
– staying close together and
– being held together by attractions called chemical bonds. Examples of chemical bonds
Electron configuration

H

H

Hydrogen gas (H2)

O

O

Oxygen gas (O2)
H

H

C

H
Methane (CH4)

H

Structural formula

Space-filling model

Ball-and-stick model

Simple Chemistry for Life Science
• Twenty-five elements are essential to people.
• Four elements make up about 96% of the weight of most cells:
– oxygen,
– carbon,

– hydrogen, and
– nitrogen.

© 2013 Pearson Education, Inc.

Simple Biochemistry for Life Science
• A cell is mostly water (H2O).

• The rest of the cell consists mainly of carbonbased molecules.
• Carbon forms large, complex, and diverse molecules necessary for life’s functions.
• Organic compounds are carbon-based molecules. Simple Chemistry for Life Science
Carbon (C): 18.5%

Oxygen (O):
65.0%
Calcium (Ca): 1.5%

Phosphorus (P): 1.0%
Potassium (K): 0.4%
Sulfur (S): 0.3%
Sodium (Na): 0.2%
Chlorine (Cl): 0.2%
Hydrogen (H):
9.5%

Nitrogen (N):
3.3%

Magnesium (Mg): 0.1%
Trace elements: less than 0.01%
Boron (B)
Chromium (Cr)
Cobalt (Co)
Copper (Cu)
Fluorine (F)
Iodine (I)
Iron (Fe)

Manganese (Mn)
Molybdenum (Mo)
Selenium (Se)
Silicon (Si)
Tin (Sn)
Vanadium (V)
Zinc (Zn)

Simple Biochemistry for Life Science
• Carbon can form an endless diversity of carbon skeletons varying in size and branching pattern.

Double bond
Carbon skeletons vary in length

Carbon skeletons may be unbranched or branched

Carbon skeletons may have double bonds, which can vary in location

Carbon skeletons may be arranged in rings

Simple Biochemistry for Life Science
• There are four categories of large biological molecules: – carbohydrates,
– lipids,
– proteins, and
– nucleic acids.

Large biological Functions molecules Carbohydrates

Components

Examples

Monosaccharides: glucose, fructose;
Disaccharides:
lactose, sucrose;
Polysaccharides:
starch, cellulose

Dietary energy; storage; plant structure Monosaccharide

Lipids

Proteins

Long-term energy storage
(fats);
hormones
(steroids)

Enzymes, structure, storage, contraction, transport, etc.

Components of a triglyceride

Side group Fats (triglycerides); steroids (testosterone, estrogen) Lactase
(an enzyme); hemoglobin (a transport protein)

Amino acid

Nucleic acids

Information storage T

Nucleotide

DNA, RNA

Carbohydrates
Functions

Components

Examples

Monosaccharides: glucose, fructose:
Disaccharides:
lactose, sucrose:
Polysaccharides:
starch, cellulose

Dietary energy; storage; plant structure Monosaccharide

Carbohydrates
• Monosaccharides are
– Simplest sugars and building block of more complex sugars
• Common examples are
– glucose in sports drinks

(a) Linear and ring structures

(b) Abbreviated ring structure Carbohydrates
• A disaccharide is
– constructed from two monosaccharides, and
– include lactose in milk, sucrose in table sugar etc.
OH

H

Glucose

Galactose
H2O

Lactose

Carbohydrates

Glucose monomer • Polysaccharides are
– complex carbohydrates

(b) Glycogen

– made of long chains of sugar units—polymers of monosaccharides.

(a) Starch

Glucose monomer (b) Glycogen

(c) Cellulose

Hydrogen bonds

• Starch

– is a familiar example of a polysaccharide,
– is used by plant cells to store energy, and
– consists of long strings of glucose monomers.
• Potatoes and grains (rice, wheat etc.) are major sources of starch in our diet.
Starch granules in potato tuber cells

• Glycogen is
– used by animals cells to store energy and
– converted to glucose when it is needed.
Glycogen granules in muscle tissue • Cellulose
– is the most abundant organic compound on Earth,
– forms cable-like fibrils in the walls that enclose plant cells, and
– cannot be broken apart by most animals.

Cellulose microfibrils in a plant cell wall
Cellulose
molecules

Lipids
Functions

Long-term energy storage
(fats);
hormones
(steroids)

Components

Fatty acid
Glycerol

Components of a triglyceride

Examples

Fats (triglycerides); steroids (testosterone, estrogen) Lipids
•

Lipids are
– hydrophobic, unable to mix with water.
– Common examples: fat, steroid, and membrane lipids

Oil (hydrophobic)
Vinegar (hydrophilic)

• A typical fat, or triglyceride, consists of
– a glycerol molecule,

– joined with three fatty acid molecules, and
– can be saturated (no C=C bonds, solid at room temperature) or unsaturated (contain C=C bonds, liquid at room temperature).

(b) A fat molecule with a glycerol “head” and three energy-rich hydrocarbon fatty acid “tails”

Saturated Fats

TYPES OF FATS
Unsaturated Fats

Margarine

Plant oils

Trans fats

Omega-3 fats

Too much fat in diet, especially saturated fat or trans fat, increases risk for cardiovascular diseases!

Proteins
Functions

Components
Amino
group

Enzymes, structure, storage, contraction, transport, etc.

Examples

Carboxyl group Side group Amino acid

Lactase
(an enzyme); hemoglobin (a transport protein)

Proteins
• Proteins
– are polymers constructed from amino acid monomers, – account for more than 50% of the dry weight of most cells,
– perform most of the tasks required for life, and
– form enzymes, chemicals that change the rate of a chemical reaction without being changed in the process.

MAJOR TYPES OF PROTEINS
Structural Proteins
(provide support)

Storage Proteins
(provide amino acids for growth)

Contractile
Proteins
(help movement)

Transport Proteins
(help transport substances) Enzymes
(help chemical reactions) Proteins
• All proteins are macromolecules constructed from a common set of 20 kinds of amino acids.
• Each amino acid consists of a central carbon atom bonded to four covalent partners.

• Three of those attachment groups are common to all amino acids: – a carboxyl group (-COOH),
– an amino group (-NH2), and
– a hydrogen atom.
• The side chain group is unique among the 20 amino acids

Amino group Carboxyl group Side group The general structure of an amino acid

Hydrophobic side group

Hydrophilic side group
Leucine

Serine

Proteins
• A functional protein consists of
– one or several long chains of amino acids called polypeptides – the sequence of amino acids in a protein is determined by its DNA
– a slight change in the amino acid sequence of a protein affects its ability to function

5

1

15

10
30

35

20

25
45

40

50

55

65
60
70

Amino acid

85

80

75

95

100

90

110

115

105
125

120
129

SEM

Leu

1

2

3

4

5

6

7. . . 146

Normal hemoglobin

SEM

Normal red blood cell

Leu

1

Sickled red blood cell

2

3

4

5

6

7. . . 146

Sickle-cell hemoglobin

Proteins
• A functional protein is
– precisely twisted, folded, and coiled into a molecule of unique shape.

– The shape enables the protein to carry out its specific function in a cell.
• Misfolded proteins are associated with

– Alzheimer’s disease,
– mad cow disease, and
– Parkinson’s disease.

Protein structure is vital to its function

Target

Protein

This shows beta-amyloid plaques (red) in the brain of an Alzheimer's disease patient.
Credit to Sanford-Burnham Medical Research Institute.

Nucleic acids
Functions

Components

Examples

Phosphate
Base

Information storage T
Sugar

Nucleotide

DNA, RNA

Nucleic Acids
• Nucleic acids are macromolecules that
– store information,
– provide the directions for building proteins, and
– include DNA (deoxyribonucleic acid) and RNA
(ribonucleic acid).

Nucleic Acids
• Nucleic acids are polymers made from monomers called nucleotides. • Each nucleotide has three parts:
1. a five-carbon sugar,
2. a phosphate group, and

3. a nitrogen-containing base.

Nitrogenous base
(A, G, C, or T)

Thymine (T)
Phosphate
group

Phosphate
Base
T
Sugar
(deoxyribose)

(a) Atomic structure

Sugar

(b) Symbol used in this book

DNA
• Each DNA nucleotide has one of four possible nitrogenous bases: – adenine (A),
– guanine (G),
– thymine (T), or

Adenine (A)

Guanine (G)

– cytosine (C).

Thymine (T)

Cytosine (C)

DNA
• Two strands of DNA join together to form a double helix.
• Bases along one DNA strand hydrogen-bond to bases along the other strand.
• The functional groups hanging off the base determine which bases pair up:
– A only pairs with T and
– G can only pair with C.

G

C
Sugar-phosphate
backbone
Nucleotide
T

T

A

Base pair T

A

Hydrogen bond G

A

T

A
A

C
T

A

G
Bases
T

C

G
A

(a) DNA strand
(polynucleotide)

T

(b) Double helix
(two polynucleotide strands)

Hydrogen bond

(b) Atomic model

RNA
• RNA is different from DNA.
– RNA uses the sugar ribose and the base uracil (U) instead of thymine (T).

Nitrogenous base
(A, G, C, or U)

– RNA is usually single-stranded, but DNA usually exists as a double helix.

Uracil (U)
Phosphate
group

Sugar (ribose)

DNA vs. RNA
DNA
Nitrogenous base Sugar
Number of strands RNA

C
G
A
T

C
G
A
U

DeoxyRibose ribose 2

1

Large biological Functions molecules Carbohydrates

Components

Examples

Monosaccharides: glucose, fructose;
Disaccharides:
lactose, sucrose;
Polysaccharides:
starch, cellulose

Dietary energy; storage; plant structure Monosaccharide

Lipids

Proteins

Long-term energy storage
(fats);
hormones
(steroids)

Enzymes, structure, storage, contraction, transport, etc.

Components of a triglyceride

Side group Fats (triglycerides); steroids (testosterone, estrogen) Lactase
(an enzyme); hemoglobin (a transport protein)

Amino acid

Nucleic acids

Information storage T

Nucleotide

DNA, RNA

INTRODUCTORY LIFE SCIENCE
At our 3rd lecture, we want to discuss

• The building blocks of biological organisms
– Carbohydrates, protein, lipids and nucleic acids

• Cell structure and function
– Cell membrane, ER, Golgi, cytoskeleton, nucleus
– Plant cell vs. animal cell

The Cell
• Cells are the lowest level of structure that can perform all activities required for life.
• Cells were first described in 1665 by Robert Hooke.
• By the mid-1800s, the accumulation of scientific evidence led to the cell theory, which states that
– all living things are composed of cells and
– all cells come from other cells.

The Cell
• Microscopes to study cells.
– Light Microscope (LM): study cells at μM (10-6 m) resolution, useful for studying live cells.
– Scanning Electron Microcope (SEM): examines cell surface at nM
(10-9 m) resolution.
– Transmission Electron Microscope (TEM): useful for studying internal structures of cells at nM (10-9 m) resolution.
TYPES OF MICROGRAPHS
Light Micrograph (LM)

Scanning Electron
Micrograph (SEM)

Transmission Electron
Micrograph (TEM)

The Cell
• All cells have several basic features.
– They are all bounded by a thin plasma membrane.

– Inside all cells is a thick, jelly-like fluid called the cytosol, in which cellular components are suspended. – All cells have one or more chromosomes carrying genes made of DNA.
– All cells have ribosomes, tiny structures that build proteins according to the instructions from the DNA.

The Cell
• Eukaryotes
– Only eukaryotic cells have organelles, membraneenclosed structures that perform specific functions.
– The most important organelle is the nucleus, which
– houses most of a eukaryotic cell’s DNA and
– is surrounded by a double membrane.

• A prokaryotic cell lacks a nucleus. Its DNA is coiled into a nucleus-like region called the nucleoid, which is not partitioned from the rest of the cell by membranes.
• We focus on eukaryotic cells from now on.

Animal cells vs. Plant cells
IDEALIZED ANIMAL CELL
Ribosomes
Cytoskeleton

Centriole
Lysosome

Plasma membrane Nucleus
Mitochondrion
Rough ER
Smooth ER
Golgi apparatus

Animal cells vs. Plant cells
Cytoskeleton
Central vacuole
Cell wall
Chloroplast

Mitochondrion
Nucleus
Rough ER
Ribosomes

Plasma membrane Channels between cells Smooth ER
Golgi apparatus

IDEALIZED PLANT CELL

Animal cells vs. Plant cells
• Unlike animal cells, plant cells have
– chloroplasts, which convert light energy to the chemical energy of food in the process of photosynthesis, and
– protective cell walls.
• Only animal cells have lysosomes, bubbles of digestive enzymes surrounded by membranes.