The Nature Of Cells

1
The Nature Of Cells
2
Cells The Smallest Unit Of Life

• Robert Hooke first saw cells in 1665 using an
  early microscope.
• Anton van Leeuwenhoek discovered living things in
  a drop of water in 1675.
• The observations of Schleiden, Schwann, and
  Virchow in the 1800s led to the modern Cell
  Theory.

• The Cell Theory has three parts
• All living things are made of cells.
• In organisms, cells are the basic unit of
  structure and function.
• Cells only come from other cells.

3
Cell Characteristics

• All cells have (1) a cell membrane, (2)
  cytoplasm, (3) ribosomes, and (4) genetic
  material.
• The first cells lived at least 3.5 billion years
  ago and were prokaryotes.
• The first cells to have internal compartments
  were the eukaryotes which appeared about 1.5
  billion years ago. Eukaryotes have a
  membrane-bound nucleus.

• Eukaryotes evolved from prokaryotes. All living
  cells that are not bacteria are eukaryotes.
• Eventually, some eukaryotes became multicellular,
  with specialized cells.
• Cells must be small to allow for transport of
  materials into and out of the cell and also
  within the cell.

Prokaryotes
Eukaryote
4
The Chemistry of Living Cells

• Atoms can also gain or lose electrons to form
  charged particles called ions, which are held
  together by their opposite charges in ionic
  bonds..

• Like all other kinds of matter, cells are made of
  atoms.
• The most common atoms in cells are C, H, O, N, P,
  and S.
• Atoms of elements can react to form molecules of
  compounds by forming covalent bonds. Covalent
  bonds are very strong and are formed in definite
  directions.

Na Cl -

• Hydrogen bonds are also important in cells.
  They are very weak, and they are different from
  other bonds because they can hold different
  molecules together as well as parts of large
  molecules like proteins.

H O H
H H H O
O O H H H
5
Water Chemistry - I

• Most cells are about 75 water.
• Water heats more slowly than most other
  substances, so it can store heat energy. Many
  organisms get rid of excess heat by the
  evaporation of water.
• Because water molecules form hydrogen bonds,
  water molecules stick to each other and to other
  molecules. This stickiness of water molecules
  causes cohesion and adhesion, major forces within
  organisms.

• Water ionizes. Therefore, pure water always
  contains a small amount of H and OH- ions.
• Because water is a polar molecule, it is also a
  very powerful solvent, able to dissolve most
  ionic compounds, and many covalent ones.
• When non-polar substances are put into water, the
  water molecules push the non-polar molecules
  together. This property of water affects the
  shape of proteins and also the structure of the
  cell membrane.

Positive end
H H O
Water is polar.
Negative end
6
Water Chemistry - II

• Any compound that forms H ions when it is
  dissolved in water is called an acid.
• Any compound that forms OH- ions when it is
  dissolved in water is called a base.

• The strength of acids and bases is measured using
  the pH scale. Neutral water has a pH of 7.0.
  Weak acids have a pH between 5 and 7. Strong
  acids have a pH below 5 and above 0. Weak bases
  have a pH between 7.0 and 9. Strong bases have a
  pH between 9 and 14.
• Many of the chemical reactions that take place
  within cells can only take place within a limited
  pH range.

14.0 very strong base
12.0 strong base
The pH scale.
9.0 weak base
7.0 neutral
5.0 weak acid
2.0 strong acid
0.0 very strong acid
7
Chemical Building Blocks of Cells - I

• All cells are made up of the same basic building
  blocks. Most of these are organic compounds,
  compounds that contain carbon.
• Macromolecules are large molecules made by
  hooking small molecules together like cars in a
  train. There are four kinds of macromolecules in
  cells
• Carbohydrates are made of C, H, and O in a 121
  ratio. Simple sugars like glucose or fructose
  are hooked together in long chains to form
  polysaccharides, such as starch, glycogen, or
  cellulose.

• Lipids store energy and are a part of the cells
  membranes. Lipids do not dissolve in water.
  There are many kinds of lipids, but they function
  in three ways energy storage, structural
  support, and as reactants in cell metabolism.
  Fats are one kind of lipid. They can be
  saturated or unsaturated. Phospholipids in the
  cell membrane are also lipids. Cholesterol and
  other steroids are also lipids.

8
Chemical Building Blocks of Cells - II

• Proteins are the third major group of
  macromolecules. Proteins form many important
  structures within organisms. Hair and
  fingernails are made of protein. Collagen, which
  is part of your skin, ligaments, tendons, and
  bones, is also a protein. Proteins also act as
  enzymes, controlling the rates of the chemical
  reactions in metabolism. Proteins are made of
  amino acids joined together in long chains called
  polypeptides. A protein is one or more
  polypeptides.

• Nucleic Acids form the fourth group of
  macromolecules. They contain hereditary
  information that directs the cells activities and
  is passed on to future generations. Nucleic
  acids are long chains of repeating units called
  nucleotides. The major job of nucleic acids is
  to store information. There are two kinds of
  nucleic acids found in living things DNA and
  RNA.

9
The Interior of the Cell - I

• In prokaryotic cells, materials can diffuse from
  one place to another.
• Eukaryotic cells are too big to move materials by
  diffusion alone.Internal membranes also transport
  materials within the cell.
• The endoplasmic reticulum (the ER) is the large
  network of membranes within the eukaryotic cell.
• The eukaryotic cell makes many proteins and
  lipids on the surface of the ER.Proteins that
  will leave the cell are made by ribosomes
  attached to the surface of the ER.

• The Golgi Apparatus packages and distributes
  proteins and lipids.
• Protein fibers provide an internal framework for
  the cell, the cytoskeleton.
• Microtubules are protein fibers that help the
  cell to move its chromosomes during cell
  division. The microtubules form organelles
  called centrioles. Plants and fungi do not have
  centrioles in their cells.
• Flagella and Cilia are threadlike projections
  from the surface of the cell that help in
  locomotion.

10
The Interior of the Cell - II

• The nucleus directs cell activities and stores
  DNA. It is the cells largest and most easily
  seen organelle.
• The nucleus rests inside of a double-layered
  membrane called the nuclear envelope. The
  activities of the cell are controlled by protein
  molecules and RNA which cross through the
  envelope.

• Inside of the nucleus is the cells genetic
  material coded into DNA molecules. The DNA and
  some structural proteins are organized together
  to form rod-like structures called chromosomes.
• All eukaryotic organisms have a definite number
  of chromosomes. Humans have twenty-three pairs
  of chromosomes (for a total of 46) in each of
  their body cells.

Cell membrane Nuclear envelope Nucleus Chromosomes
11
The Interior of the Cell - III

• Specialized organelles act as powerhouses of the
  cell.
• Two kinds of organelles are important in energy
  release and food manufacture, mitochondria and
  chloroplasts.
• Mitochondria are found in almost all eukaryotic
  cells and release the energy that is stored in
  food so that the cell can use it.
• Chloroplasts are found only in plants and algae.
  They are the organelles that capture the suns
  energy and store it in the form of sugar.

• Other organelles act as biochemical factories.
• Peroxisomes contain several kinds of enzymes.
  Some convert fats to carbohydrates. Others
  change harmful molecules within the cell into
  H2O2, which is then changed into water.
• Lysosomes are part of the cells digestive
  system. They break down nucleic acids, lipids,
  proteins, and carbohydrates so that their
  building blocks can be recycled.
• Vacuoles are used to store water, wastes, and
  nutrients.

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Animal Cell
Peroxisomes Golgi Apparatus Nucleolus Chromosom
es Lysosomes Cytoplasm
Cell Membrane Centrioles Endoplasmic
Reticulum with ribosomes Nuclear
envelope Nucleus Mitochondria Food vacuole
13
Plant Cell
Nuclear Envelope Nucleus Chromosomes Nucleolus En
doplasmic Reticulum with ribosomes Mitochondrion
Cytoplasm
Cell Wall Cell Membrane Golgi Apparatus Leucoplas
t Central Vacuole Chloroplast