Elements in Cells
• The living substance of cells is made up of cytoplasm and the structures within it.
• About 96% of cytoplasm and its included structures are composed of the elements carbon, hydrogen, oxygen, and nitrogen.
▫ 3% from phosphorus, potassium and sulfur
▫ 1% from calcium, iron, magnesium, sodium,
chlorine, copper, manganese, cobalt, zinc and
minute quantities of other elements
Elements in Cells
• When a plant first absorbs these elements from the soil or atmosphere, or when it breaks down products within the cell, the elements are in the form of
simple molecules or ions.
• These simple forms may be converted to very large, complex molecules through the metabolism of the cells.
• The large molecules have “backbones” of carbon atoms within them and are said to be organic.
• The countless number of chemical reactions of living organisms is based on organic compounds.
Carbon-organic Compounds
• In their outer shells, carbon atoms have four electrons that can bond with other atoms.
• When carbon is bonded to hydrogen, which is common in organic molecules, the carbon atom shares an electron with hydrogen, and hydrogen likewise share an electron with carbon.
• Carbon-hydrogen molecules are referred to as hydrocarbons.
• Nitrogen, sulfur, and oxygen also are often joined to carbon in living organisms.
Building Cells from Four Types of Molecules
• The cells of all living things, including plant cells, are primarily made of four types of big molecules, called
macromolecules:
Carbohydrates
Lipids
Proteins
Nucleic acids
Carbohydrates
• Carbohydrates, commonly called sugars, are the most abundant organic compounds in nature.
• Carbohydrates contain carbon, hydrogen, and oxygen in a ratio of 1C:2H:1O.
• The formula can be multiplied, for example, glucose has the formula C6H12O6. The basic ratio is the
same.
• Cells use carbohydrates for:
▫ Storing energy and
▫ Building materials and
▫ To provide structure to the cell.
Carbohydrates
• Monosaccharides - Simple sugars with backbones of
three to seven carbon atoms.
(Glucose and Fructose)
• Glucose fast source of energy
Carbohydrates
• Monosaccharides may form bonds with each other to form larger structures.
▫ Disaccharides - Formed when two
monosaccharides (simple sugars) bond together by dehydration synthesis.
(glucose + fructose = sucrose)
▫ Polysaccharides - Formed when several to
many (some thousands) of monosaccharides
bond together. (Cellulose)
Carbohydrates
• Carbohydrates are in nearly every food, not just
bread and pasta, which are know for “carbo loading.”
• Fruits, vegetables, and meats also contain carbohydrates.
• Any food that contains sugars contains carbohydrates.
• Most foods are converted to sugars when they are digested.
• Plants and animals both store sugars. In animals it is glycogen
• The storage form of glucose in plants is starch.
Lipids
• Lipids are fatty or oily substances that are mostly insoluble in water. (Fats and Oils)
• Glycerol (or other alcohol) + three fatty acids
▫ Typically store twice as much energy as carbohydrates.
Most consist of chain with 16-18 carbon atoms.
Saturated - No double bonds, H atoms attached to every available bond of their C atoms
Unsaturated - At least one double bond between carbon atoms.
Glycerol (or other alcohol) + three fatty acids
Saturated - No double
bonds, H atoms attached to every available bond of their C atoms
Unsaturated - At least one double bond between carbon atoms.
Lipids
• Lipids serve many important functions.
▫ Store energy
▫ Protection against dehydration and pathogens
▫ Carry electrons and absorb light
▫ Contribute to structure of membranes
▫ Agricultural commodities important to
the food, medical, and manufacturing
industry
Lipids
• Because plants can’t control their temperatures, they contain much more oil than fats.
• Waxes - Lipids consisting of long-chain fatty acids bonded to long chain alcohol other than glycerol.
▫ Example: In plants, waxes, cutin, and suberin protect against dehydration and pathogens.
• Phospholipids - Constructed like fats, but one of the fatty acids is usually replaced by a phosphate group.
▫ Example: found in cell membranes
Proteins, Polypeptides, and Amino Acids
• Proteins perform essential jobs in cells.
▫ Help chemical reactions
▫ Support the cell
▫ Move materials around
▫ Control information flow
▫ Send signals
Proteins, Polypeptides, and Amino Acids
• Proteins are usually very large and consist of one or more polypeptide chains.
▫ Polypeptides are chains of amino acids.
▫ 20 different amino acids.
Each amino acid has two functional groups plus an R group.
Amino group (-NH
2)
Carboxyl group (-COOH)
Proteins, Polypeptides, and Amino Acids
Proteins, Polypeptides, and Amino Acids
• Polypeptide Structure- To make a protein amino
acids bond with covalent bonds called peptide bonds
▫ Primary Structure - A sequence of amino acids fastened together by peptide bonds.
▫ Secondary Structure - Coiling of polypeptide chains.
▫ Tertiary Structure - Maintained by coils between R groups.
▫ Quaternary Structure - Occurs when a protein has more than one kind of polypeptide.
Proteins, Polypeptides, and Amino Acids
• Structural proteins support the cell.
▫ Cytoskeletal proteins provide supportive scaffolding from the inside of the cell.
▫ Outside the cell, proteins are woven into
the cell wall, a protective layer that encases
a plant cell.
Proteins, Polypeptides, and Amino Acids
•
Transport proteins move materials into and within plant cells.
•
Proteins located at the boundary of the cell help create passageways for
materials.
•
Inside the cells, structures may use
cytoskeletal proteins as tracks that allow
them to move around the cell.
Proteins, Polypeptides, and Amino Acids
• Enzymes are proteins that speed up chemical reactions.
• Enzymes are mostly large, complex
proteins that function as organic catalysts under specific conditions.
▫ Work by lowering energy of activation.
Temporarily bonds with potentially reactive molecules at a surface site.
Names end in =ase.
Nucleic Acids
• Nucleic acids are very large, complex polymers.
▫ Vital to internal communication and cell functioning.
▫ Two types of nucleic acids.
Deoxyribonucleic Acid (DNA) and
ribonucleic acid (RNA) are composed of nucleotides.
Three parts- nitrogenous base, five-carbon sugar, and a phosphate.
DNA does not leave the nucleus of the cell.
Nucleic Acids
• DNA stores the information that determines the structure and function of all cells on earth.
• DNA determines the traits of plants.
• When cells reproduce, they copy their DNA molecules and pass them on to the new cells.
• RNA is similar to DNA in structure, but more flexible in its functions. Different types perform different functions.
• Some carry information around the cell.
• Some help build proteins.
• Some control when proteins are made.
• RNAs contain information, but they can move around and cause things to happen.
Review
• Attributes of Living Organisms
• Chemical and Physical Bases of Life
• Molecules
• Bonds and Ions
• Acids and Bases
• Carbohydrates, Lipids, Proteins
• Enzymes
• Nucleic Acids
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