Ch15 l the basic unit of life

Chapter 15The Basic Unit of

Life- The Cell

Principles of Science II

This lecture will help you understand:

1. Characteristics of Life2. Macromolecules Needed for Life3. Cell Types: Prokaryotic and Eukaryotic4. The Microscope5. Tour of a Eukaryotic Cell6. The Cell Membrane7. Transport into and out of Cells8. Cell Communication9. How Cells Reproduce10.How Cells Use Energy11. ATP and Chemical Reactions in Cells12.Photosynthesis 13.Cellular Respiration and Fermentation

Characteristics of Life

• All living things – use energy.– develop and grow.– maintain themselves.– have the capacity to reproduce.– are parts of populations that evolve.


• All living things use energy.– Plants take electromagnetic energy from sunlight and

convert it to chemical energy.– Animals convert energy from food into chemical

energy.– Living things use this chemical energy to build

structures and fuel their activities.– How living things use energy is consistent with the

laws of physics.


• All living things develop and grow, changing over time.

• Living things maintain themselves.– They build structures (bones, stems).– They repair damage (heal wounds).– They maintain their internal environments (body

temperature, water balance).


• All living things have the capacity to reproduce.– Asexual reproduction occurs when an organism

reproduces by itself.

– Sexual reproduction occurs when organisms produce sperm and eggs that join to develop into new individuals.


• All living things are parts of populations that evolve.– Populations do not remain constant.– Populations change over time, across generations.– Populations may evolve in response to their

environments.

Macromolecules Needed for Life

• Proteins (amino acid Leucine)• Carbohydrates (Glucose)• Lipids (Palmitric Acid)• Nucleic acids (Guanine DNA)

Cell Types: Prokaryotic and Eukaryotic

• Prokaryotic cells have no nucleus.• Prokaryotes are almost always

single-celled, microscopic organisms. Their DNA is found in a single circular structure. They usually have an outer cell wall.

Cell Types: Prokaryotic and Eukaryotic

• Eukaryotic cells have a nucleus and may be single-celled or multicellular. They– have their DNA inside the nucleus.– have linear chromosomes.– have various organelles.– are larger than prokaryotic cells.

The Microscope

• Light microscopes allow people to view cells and make out the larger features within them.

• Electron microscopes allow people to view even smaller structures within cells.

The Microscope

Light microscope

The Microscope

Electron microscope

Tour of a Eukaryotic Cell

• Eukaryotic cells contain many parts, including:– Cell membrane– Nucleus– Cytoplasm– Cytoskeleton– Organelles

• All the parts of the cell have specific functions.

Tour of a Eukaryotic Cell

• Plant cells also contain (animal cells do NOT)– a cell wall to make the cell rigid. – chloroplasts that perform photosynthesis.

The Cell Membrane

• The cell membrane– defines a cell's boundary.– controls what moves into and out of the cell.– consists of a phospholipid bilayer, membrane

proteins, and short carbohydrates.

The Cell Membrane

• The fluid mosaic model describes the structure of the cell membrane, a mosaic of proteins and phospholipids, almost all of which can move fluidly around the membrane.

Transport into and out of cells

• Cells take in many resources, including water, oxygen, and organic molecules.

• Cells also discard wastes. • Transport occurs through:

– Diffusion– Facilitated diffusion– Active transport– Endocytosis and exocytosis

• Diffusion is the tendency of molecules to move from an area of high concentration to an area of low concentration. – Molecules diffuse

across the phospholipid bilayer of the cell membrane.

– Diffusion requires no energy from the cell. It is a form of passive transport.



• Facilitated diffusion occurs when a transport protein binds to a molecule and moves it down a concentration gradient. – Facilitated diffusion requires no energy from the cell.

It is a form of passive transport.


• Active transport occurs when a transport protein moves a molecule against its concentration gradient.– Active transport requires energy from the cell.


• Larger amounts of material can be transported into and out of cells through endocytosis and exocytosis.– In endocytosis, a vesicle pinches off from the cell

membrane.– In exocytosis, a vesicle fuses with the cell membrane.

Cell Communication

• Cells communicate with one another using special molecules.

• Communication between adjacent cells occurs when molecules move from one cell to another through special "doorways."– Animal cells have gap junctions.– Plant cells have plasmodesmata.

Cell Communication

• Long-distance communication relies on message molecules traveling through the bloodstream.– Receptors are membrane proteins.– A receptor binds a message molecule with a lock-and-

key fit.– The binding of the receptor to a message molecule

initiates a series of chemical reactions that results in the target cell's response to the message.

Cell Communication

How Cells Reproduce

• In mitosis, one parent cell divides into two daughter cells that have the same genetic information as the parent cell.

How Cells Reproduce

• A dividing cell goes through the stages of the cell cycle:

1. Gap 1

2. Synthesis

3. Gap 2

4. Mitosis/cytokinesis

How Cells Reproduce

• The phases of mitosis:

1. Prophase: Chromosomes condense, and nuclear membranes break down.

2. Metaphase: Chromosomes line up along the equatorial plane.

3. Anaphase: Sister chromatids are pulled apart and move to opposite poles of the cell.

4. Telophase: New nuclear membranes form around each set of chromosomes.

• After mitosis, cytokinesis occurs: The cytoplasm divides, completing cell division.

How Cells Reproduce

How Cells Use Energy

• Two things are necessary for a chemical reaction to occur:– Must be consistent with the law of conservation of

energy.• Exothermic (energy-releasing) reactions occur

spontaneously. • For all other reactions, cells rely on usable energy

stored in molecules of ATP.– Activation energy needed for initial breaking of bonds.


• ATP provides energy for chemical reactions in cells.• Cells obtain energy from ATP when one phosphate

group is removed, leaving ADP.


• Cells eventually turn ADP back into ATP by adding a phosphate group during cellular respiration.


• The sodium-potassium pump uses active transport to control the levels of sodium ions (Na+) and potassium ions (K+) in cells. This process uses one molecule of ATP.


• Reacting molecules must collide with an activation energy that is needed for the initial breaking of bonds.

• The activation energy for many essential chemical reactions is very high.

• A catalyst is a substance that lowers the activation energy, allowing a reaction to happen more quickly.

• The catalysts in cells are enzymes—large, complex proteins.


• An enzyme binds the reactants at its active site and releases the products.

• In the process, the enzyme is not altered or destroyed; it can be used again and again.


• Cells regulate enzymes– Cells control the synthesis and degradation of

enzymes.– Enzyme function depends on temperature, pH, and

other features of the environment.– Inhibitors can block the function of enzymes.


• Two types of enzyme inhibition

– In competitive inhibition, the inhibitor binds to the active site of an enzyme so that the enzyme cannot bind its substrate.

– Noncompetitive inhibition occurs when an inhibitor binds to a different part of the enzyme, changing the active site so that the enzyme can no longer bind to its substrate.

Photosynthesis

• The process organisms use to convert light energy from the Sun into chemical energy.

• Conducted in the chloroplasts of plants.• Occurs in two stages: the light-dependent reactions and

the light-independent reactions.• Photosynthesis is the ultimate source of (practically) all

organic molecules on Earth.

Photosynthesis

Light-dependent reactions

Photosynthesis

• Light-independent reactions– The light-independent reactions make use of stored

energy from the light-dependent reactions.

– Carbon is fixed, moved from atmospheric CO2 to the sugar glucose.

– The molecules produced during photosynthesis are used as a starting point for building all of the macromolecules of life.

Cellular Respiration and Fermentation

• Cells break down glucose to produce ATP.• Cellular respiration is aerobic (uses oxygen).• Cellular respiration yields 38 molecules of ATP

from every molecule of glucose.


• Cellular respiration occurs in three steps:– Glycolysis– The Krebs cycle– Electron transport


• Glycolysis takes place in the cytoplasm of cells.– The glucose molecule is split into two

molecules of pyruvic acid, releasing two molecules of ATP.


• The Krebs cycle occurs in the cell's mitochondria.– In the Krebs cycle, pyruvic acid is converted to acetic

acid and bound to a molecule of coenzyme A. The result—acetyl-CoA—is broken down into CO2.

– Two molecules of ATP are harvested. Additional energy is stored in the molecules NADH and FADH2.


• In electron transport, electrons carried by NADH and FADH2 are sent down electron transport chains. – In the process, the electrons lose energy, which is

used to pump hydrogen ions across a membrane inside the mitochondria.

– At the end of the chain, the electrons combine with O2 to make water.

– The concentration gradient generated by pumping hydrogen ions is used to make ATP.


• In certain cells, under certain conditions, glycolysis is followed by fermentation.

– Fermentation uses no oxygen and generates no ATP. – But, fermentation regenerates the molecules

necessary to keep glycolysis going, so cells can continue to obtain energy through glycolysis.

• Alcoholic fermentation by yeast is used to bake bread and make beer and wine.

• Lactic acid fermentation occurs in muscle cells when there is not enough oxygen for cellular respiration to continue. It is also used by red blood cells. Lactic acid fermentation by bacteria and yeast is used to make yogurt and cheese.