CHAPTER 3 The Molecules of Cells

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CHAPTER 3The Molecules of Cells

• Lifes structural and functional diversity
  results from a great variety of molecules
• A relatively small number of structural patterns
  underlies lifes molecular diversity

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Organic Compounds

• Always contain carbon
• Tend to be large complex
• A carbon atom forms four covalent bonds (this
  allows carbon to form many different chemical
  compounds)
• Carbon skeletons vary in many ways

Carbon skeletons vary in length.
Skeletons may be unbranched or branched.
Skeletons may have double bonds, which can vary
in location
Skeletons may be arranged in rings
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Cells make a huge number of large molecules from
a small set of small molecules

• Most of the large molecules in living things are
  macromolecules called polymers
• Polymers are long chains of smaller molecular
  units called monomers (building blocks)
• A huge number of different polymers can be made
  from a small number of monomers
• SIZE monomerlt polymerlt macromolecule

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Making and Breaking of POLYMERS

• Cells link monomers to form polymers by
  dehydration synthesis (building up)

Short polymer
Unlinked monomer
Removal ofwater molecule
Longer polymer
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Making and Breaking of POLYMERS

• Polymers are broken down to monomers by the
  reverse process, hydrolysis (hydro add water
  lysis to split)

Addition ofwater molecule
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1. CARBOHYDRATES

• They range from small sugars to large
  polysaccharides

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Monosaccharides are the simplest carbohydrates

• Monosaccharides are single-unit sugars
• These molecules typically have a formula that is
  a multiple of CH2O
• Monosaccharides are the fuels for cellular work

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Cells link single sugars to form disaccharides

• Monosaccharides can join to form disaccharides,
  such as sucrose (table sugar) and maltose
  (brewing sugar)

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Polysaccharides are long chains of sugar units

• polymers of hundreds or thousands of
  monosaccharides linked by dehydration synthesis
• Function as
• Energy storage
• Starch (plants)
• Glycogen (animals)
• Structure
• Cellulose (plants cell walls) (fiber in diet)
• Chitin ( insects)

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Lipids

• composed largely of carbon and hydrogen
• They are not true polymers
• They are grouped together because they do not
  mix with water (Nonpolar)

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Lipids include fats,

• Fats are lipids whose main function is long term
  energy storage
• Other functions
• Insulation in higher vertebrates
• shock absorber for internal organs
• A triglyceride molecule consists of one glycerol
  molecule linked to three fatty acids

Fatty acid
Fatty acid
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Saturated Unsaturated fats

• fatty acids of unsaturated fats (plant oils)
  contain double bonds
• These prevent them from solidifying at room
  temperature
• Saturated fats (lard) lack double bonds
• They are solid at room temperature

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Phospholipids, waxes, and steroids are lipids

• Phospholipids are a major component of cell
  membranes
• Waxes form waterproof coatings
• Steroids are often hormones

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Cholesterol (only in animal cells)

• an important steroid is a component in animal
  cell membranes.
• Used to make many of the bodys steroid hormones
• Forms sheath for some nerve cells
• While important, high levels in the blood may
  contribute to cardiovascular disease

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Connection Anabolic steroids

• Anabolic steroids are usually synthetic variants
  of testosterone
• Use of these substances can cause serious health
  problems

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PROTEINS

• essential to the structures and activities of
  life
• Make up 50 of dry weight of cells
• Contain carbon, hydrogen, oxygen PLUS nitrogen
  and sometimes sulfur
• Proteins are involved in
• cellular structure
• movement
• defense
• transport
• Communication
• Monomers are called amino acids

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Proteins are made from just 20 kinds of amino
acids

• Proteins are the most structurally and
  functionally diverse of lifes molecules
• Their diversity is based on different
  arrangements of amino acids
• R- variable group- which distinguishes each of
  the 20 different amino acids

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Amino acids can be linked by peptide bonds

• Cells link amino acids together by dehydration
  synthesis
• The bonds between amino acid monomers are called
  peptide bonds

PEPTIDEBOND
Dehydrationsynthesis
Dipeptide
Amino acid
Amino acid
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A proteins specific shape determines its function

• A protein consists of polypeptide chains folded
  into a unique shape
• The shape determines the proteins function
• A protein loses its specific function when its
  polypeptides unravel

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A proteins specific shape determines its function

• A protein can change in response to the physical
  and chemical conditions
• Alterations in pH, salt concentration,
  temperature, or other factors can unravel or
  denature a protein
• Some proteins can return to their functional
  shape after denaturation -renature

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NUCLEIC ACIDS

• 1. DNA (deoxyribonucleic acid) contains the
  instructions used to form all of an organisms
  proteins.
• 2. RNA (ribonucleic acid) forms a copy of DNA
  for use in making proteins.
• They ultimately control the life of a cell

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NUCLEIC ACIDS

• The monomers of nucleic acids are nucleotides
• Each nucleotide is composed of a sugar,
  phosphate, and nitrogenous base

Nitrogenousbase (A)
Phosphategroup
Sugar
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NUCLEIC ACIDS

• The sugar and phosphate form the backbone for the
  nucleic acid

Nucleotide
Sugar-phosphatebackbone
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DNA

• DNA consists of two polynucleotides twisted
  around each other in a double helix
• Base pairing
• A T
• G - C
• The sequence of the four kinds of nitrogenous
  bases in DNA carries genetic information

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DNA

• Stretches of a DNA molecule called genes program
  the amino acid sequences of proteins
• DNA information is transcribed into RNA, a
  single-stranded nucleic acid
• RNA is then translated into the primary structure
  of proteins