Chapter 24The Chemistry of Life

Structure of CellsOrganisms are composed of as few as one cell or as many as billions of cells.

Two major cell types occur in nature

1. Prokaryotic [proh-kar-ee-ot-ik] cells – the cells of bacteria

2. Eukaryotic [yoo-kar-ee-ot-ik] cells – the cells of all other organisms

Prokaryotic cells were present on Earth at least 3 billion years ago.

Eukaryotic cells did not appear until about 1 billion years ago.

Both cell types contain all the chemicals necessary for life, encased in a cell membrane.

Structure of CellsThe cell membrane is a sack that holds the contents of a cell and acts as a selective barrier for the passage of substances into and out of the cell

Eukaryotic cells are considerably larger and more complex than prokaryotic cells. They can also vary greatly in size and shape.

The chemical processes carried out by both types of cells are very similar.

Eukaryotic cells contain membrane-enclosed organelles, prokaryotic cells do not.

Organelles (little organs) are small structures suspended in the interior cellular fluid, or cytoplasm.

Prokaryotic Cells

• Believed to be the first cells to evolve.

• Lack a membrane bound nucleus and organelles.

• Genetic material is naked in the cytoplasm

• Ribosomes are only organelle.

Cell Wall

• Rigid coat that gives the cell shape and surround the cytoplasmic membrane.

• Offers protection from environment.

Plasma Membrane

• Layer of phospholipids and proteins that separates cytoplasm from external environment.

• Regulates flow of material in and out of cell.

Cytoplasm• Also known as

protoplasm

• Is location of growth, metabolism, and replication.

• Gel-like matrix of water, enzymes, nutrients, wastes, and gases

• Contains cell structures.

Ribosomes

• Translate the genetic code into proteins.

• Free-standing and distributed throughout the cytoplasm.

Nucleoid

• Region of the cytoplasm where chromosomal DNA is located.

• Usually a singular, circular chromosome.

• Smaller circles of DNA called plasmids are also located in cytoplasm.

Mesosome• Infolding of cell

membrane.

• Possible role in cell division.

• Increases surface area.

• Photosynthetic pigments or respiratory chains here.

Eukaryotic Cells

• “True nucleus”; contained in a membrane bound structure.

• Membrane bound organelles.

• Thought to have evolved from prokaryotic cells.

Ribosomes

• Translate the genetic code into proteins.

• Found attached to the Rough endoplasmic reticulum or free in the cytoplasm.

Rough Endoplasmic Reticulum

• Network of continuous sacs, studded with ribosomes.

• Manufactures, processes, and transports proteins for export from cell.

Smooth Endoplasmic Reticulum

• Similar in appearance to rough ER, but without the ribosomes.

• Involved in the production of lipids, carbohydrate metabolism, and detoxification of drugs and poisons.

• Metabolizes calcium.

Lysosome

• Single membrane bound structure.

• Contains digestive enzymes that break down cellular waste and debris and nutrients for use by the cell.

Golgi Apparatus

• Modifies proteins and lipids made by the ER and prepares them for export from the cell.

• Encloses digestive enyzymes into membranes to form lysosomes.

Mitochondrion• Membrane bound

organelles that are the site of cellular respiration

Nucleus

• Double membrane-bound control center of cell.

• Separates the genetic material from the rest of the cell.

Parts of the nucleus:

• Chromatin - genetic material of cell in its non-dividing state.

• Nucleolus - dark-staining structure in the nucleus that plays a role in making ribosomes

• Nuclear envelope - double membrane structure that separates nucleus from cytoplasm.

Plasma Membrane

• Phospholipid bilayer that separates the cell from its environment.

• Selectively permeable to allow substances to pass into and out of the cell.

Cilia and Flagella

• External appendages from the cell membrane that aid in locomotion of the cell.

• Cilia also help to move substance past the membrane.

Centrioles

• Found only in animal cells.

• Self-replicating

• Made of bundles of microtubules.

• Help in organizing cell division.

Microfilaments

• Solid rods of globular proteins.

• Important component of cytoskeleton which offers support to cell structure.

Cell Wall

• Protects and gives rigidity to plant cells

Chloroplast

• Site of photosynthesis

• Membrane bound structure.

• Contains chlorophyll

Vacuole

• Plants have large central vacuoles that store water and nutrients needed by the cell.

• Help support the shape of the cell.

Animal Cell vs. Plant Cell

Prokaryotic vs. Eukaryotic

PhotosynthesisOrganisms must have energy to survive. The ultimate source of this energy is the sun.

Cells of green plants and certain algae contain organelles called chloroplasts that are able to capture solar energy and make food.

Within the chloroplast is a light-capturing system that converts light energy into chemical energy by a process called photosynthesis.

Photosynthesis uses the energy from sunlight to reduce carbon dioxide to compounds that contain C-H bonds, mainly in the form of glucose.

Overview of Photosynthesis6 CO2 + 6 H2O → C6H12O6 + 6 O2

light energy

Photosynthesis is the process of converting light energy into food energy (glucose, chemical energy stored in chemical bonds).

Photosynthesis carried out by plants and algae.

Photosynthesis

Animals, that do not carry out photosynthesis, get the carbon compounds used by all organisms by eating plants or by eating animals that feed on plants.

Both plants and animals get energy by unleashing the energy stored in the chemical bonds of these carbon compounds.

The nutrients are oxidized back to carbon dioxide and water in the process.

C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + energy

PhotosynthesisPlant life could survive without animals, but animal life could never survive without plants.

Oxygen is an important product of photosynthesis

Photosynthetic organisms produce the oxygen found in Earth’s atmosphere.

End of Section 24.1

End of Section 24.2

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Amino Acids

• Building blocks of proteins

• Carboxylic acid group

• Amino group

• Side group R gives unique characteristics

R side chain I

H2N—C —COOH I

H

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Examples of Amino Acids

H I

H2N—C —COOH I

H glycine

CH3

I

H2N—C —COOH I

H alanine

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Types of Amino Acids

Nonpolar R = H, CH3, alkyl groups, aromatic

OPolar ll

R = –CH2OH, –CH2SH, –CH2C–NH2,

(polar groups with –O-, -SH, -N-)

Polar/Acidic

R = –CH2COOH, or -COOH

Polar/ Basic

R = –CH2CH2NH2

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The Peptide Bond

Amide bond formed by the –COOH of an amino acid and the –NH2 of the next amino acid

O CH3

+ | | + |

NH3–CH2–COH + H3N–CH–COO–

O CH3

+ | | |

NH3–CH2–C – N–CH–COO–

| peptide bond H

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Peptides

• Amino acids linked by amide (peptide) bonds

Gly Lys Phe Arg Ser

H2N- -COOH

end Peptide bonds end

Glycyllysylphenylalanylarginylserine

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