Basic Biology I Review Unit 2

VI. Cell Structure

The basic unit of life is the cell. The cell theory states 1) all organisms are composed of cells, (2) the cell is the basic unit of organization of organisms, (3) all cells come from preexisting cells.

There are 2 basic cell types, those with internal, membrane-bound organelles (eukaryotes) and those without (prokaryotes). Bacteria and archaebacteria are prokaryotic; all others are eukaryotic.

Organelle functions are shown below.

Organelle / Function
Plasma membrane / Controls movement of substances into & out of the cell; maintains homeostasis
Cell wall / Provides protection and support for plant cells
Cytoplasm / Suspends cell organelles & is site of many chemical reactions
Nucleus / Controls cellular activity by housing DNA, the blueprints for cellular proteins
Nucleolus / RNA & ribosome synthesis
Ribosome / Protein synthesis
Endoplasmic reticulum (ER) / Site of cellular chemical reactions. Rough ER - protein production. Smooth ER - production & storage of lipids
Golgi apparatus / Sort & package proteins
Vacuole / Temporary storage of materials
Lysosome / Digest excess or worn out organelles, food particles, and engulfed viruses or bacteria
Chloroplast / Plant organelle that captures light energy & produces food to store for later
Plastids / Plant organelle used for storage of starches, lipids, pigments, etc...
Mitochondrion / “Powerhouse of the cell”; site of cellular respiration
Cytoskeleton / Support structure for cell; assists in movement of organelles
Cilia & flagella / Locomotion
Mitotic spindle / Separates chromosomes in mitosis

VII. Cellular Transport

A. Osmosis

1. Diffusion of water (from area of higher concentration to lower conc.) across a selectively

permeable membrane

2. Regulation is important for maintaining homeostasis

a. Concentration gradient controls osmosis

3. Isotonic solution

a. the concentration of dissolved substances is equal between the cell & its environment

b. cells do not experience osmosis or any change in shape

4. Hypotonic solution

a. the concentration of dissolved substances is lower in the environment than in the cell

b. the concentration of water is therefore HIGHER in the environment than in the cell

c. the water rushes INTO the cell, causing the cell to increase in volume & possibly burst

5. Hypertonic solution

a. the concentration of dissolved substances is higher in the environment than in the cell

b. the concentration of water is therefore LOWER in the environment than in the cell

c. the water therefore rushes OUT of the cell, causing the cell to shrink in volume;

loss of water in plant cells results in a drop in pressure, causing the plant to wilt

B. Passive Transport

1. water, lipids, & lipid-soluble substances pass through the plasma membrane by diffusion

2. NO ENERGY is required for this movement down their concentration gradients

3. movement across the membrane via transport proteins = FACILITATED DIFFUSION

C. Active Transport

1. Definition = movement of substances AGAINST their concentration gradients, requiring the

expenditure of energy

2. A CARRIER PROTEIN has a shape that fits its particular molecule or ion & binds with that

substance (to be transported) near the cell membrane. When the carrier protein binds it, chemical energy allows for a change in the shape of the protein which allows the

carrier protein with its substance to be moved across the membrane. The carrier protein

then resumes its original shape, allowing the substance to be released on the other side.

3. Endocytosis:

The cell encloses material from its environment with its plasma membrane & engulfs it.

That portion of the membrane breaks away to create a vacuole inside the cell.

4. Exocytosis:

The expulsion or secretions of materials from the cell occurs when the vacuole merges

with the plasma membrane and then "bursts" its contents into the environment.

VIII. Photosynthesis (performed by autotrophs)

A. Two Main Phases

1. Light Reaction

a. Depends on sunlight, activated electrons of chlorophyll, & accessory proteins

b. Multi-step process:

  • Sunlight activates electrons of chlorophyll a found in thylakoid membranes of chloroplasts
  • Accessory pigment molecules of both photosystem I & II absorb light; energy passed to chlorophyll a molecules of photosystem II
  • Having lost electrons, chlorophyll a molecules are oxidized; the accompanying reduction, or acceptance of electrons, is accomplished by the primary electronacceptor.
  • The primary electron acceptor donates electrons to a series of molecules in the thylakoid membranes called the electron transport chain. As electrons are passed, some energy is lost to help move protons (H+) across the thylakoid membrane to create a gradient/energy source.
  • At the same time that light energy is being absorbed by photosystem II, it is also being harnessed by photosystem I. Another pair of molecules in chlorophyll a has its electrons activated & transported down a different electron transport chain. This chain brings electrons to the side of the thylakoid membrane facing the stroma to combine with H+& NADP+.
  • Electrons from chlorophyll a in photosystem II replace electrons leaving chlorophyll a in photosystem I. To replenish photosystem II’s chlorophyll a’s electrons, water is cleaved in the thylakoid membranes (photolysis): 2 H2O  4 H+ + O2 + 4e- Oxygen diffuses out of the plant.
  • Chemiosmosis is fueled by the H+ gradient (more concentrated in thylakoid than in the stroma). This allows ATP synthase in the thylakoids to produce ATP from ADP + phosphate.

2. “Dark Reaction” = Calvin Cycle

a. Does NOT depend on light nor on darkness, only on energy molecules & CO2

b.Multi-step process:

  • Carbon fixation occurs in the stroma as C molecules fromair’s CO2 combine with a ribulose bisphosphate (RuBP) in a cyclic fashion to form an unstable 6-C molecule which breaks down into 2 molecules of phosphoglyeric acid (PGA).
  • PGA + energy from ATP & NADPH forms phosphoglyceraldehyde (PGAL) & eventually glucose

B. 6 CO2 + 6 H2O + light energy  C6H12O6 + CO2 {Classic general formula for photosynthesis)

6 CO2 (picked up by 6 RuBP)  12 PGA + 12 ATP + 12 NADPH  12 PGAL  (2 PGAL C6H12O6) + 10 PGAL + 6 ATP  6 RuBP. This actually is a 1-C-at-a-time process.

IX. Cellular Respiration

X. Cell Growth & Reproduction

A. Cell Size Limitations

1. Most cells range between 2-200 m in diameter.

a. Nerve cells can be 1 meter long.

b. Ostrich egg yolk is 8 cm across.

2. Nutrients & wastes typically move by diffusion which works fine for short distances only.

3. The rate of transcription (copying DNA into mRNA) & translation (making proteins from

the mRNA code) can limit size. Cells need sufficient DNA for all the proteins needed.

a. Larger cells with lots of cytoplasm often have evolved to have >1 nucleus with DNA.

4. Cell's surface area-to-volume ratio must balance availability of nutrient & waste transport

via the plasma membrane with the amount of cytoplasmic activities necessary to live.

B. Cell Reproduction

1. Cell division is the process by which new cells are produced from one cell.

a. Chromosomes become visible in the nucleus just before & during cell division.

b. Chromosomes carry cell's genetic material as DNA in a tightly packed arrangement.

2. Cell Cycle

a. Definition: the sequence of growth & division of a cell.

b. Has 2 general periods:

1) Interphase - Growth of cell & replication of chromosomes

G1 phase: protein synthesis & growth

S phase: replication of chromosomes to form identical sister chromatids

G2 phase: chromosomes shorten & coil; much protein synthesis; centriole

pair replicates & mitotic spindle forms in animal cells.

2) Mitosis - Period of nuclear divisions; process where 2 daughter cells form 4 stages resulting in formation of 2 daughter cells of identical copies of DNA

c. Cytokinesis = division of cytoplasm following mitosis

3. Mitosis

  1. Prophase: 1st phase
  • Long, stringy chromatin coils up into visible chromosomes
  • Each duplicated chromosome is made up of 2 halves = sister chromatids
  • Sister chromatids with their DNA are EXACT COPIES of each other
  • Sister chromatids are connected by a centromere
  • Nucleus & nucleolus disappear by the end of prophase
  • Centrioles (animals) made of microtubules migrate to opposite poles of cell
  • The mitotic spindle forms between the centrioles

b. Metaphase: 2nd phase

  • Centromeres of sister chromatids attach to the mitotic spindle
  • Centromeresline up on the midline of the spindle
  • Each sister chromatid attaches to its own spindle fiber
  • Sister chromatid’s spindle fiber attaches to opposite poles

c. Anaphase: 3rd phase

  • Separation of sister chromatids
  • Centromeres split apart & chromatid pairs of each chromosome separate
  • Chromatids are pulled apart by shortening of microtubules in the spindle

d. Telophase: 4th phase

  • Begins as chromatids reach the opposite poles of the cell
  • Chromosome begin to unwind to direct activities of the new cells
  • Mitotic spindle breaks down
  • Nucleolus reappears
  • Nuclear envelope forms around each set of chromosomes
  • Plasma membrane begins to form between the 2 new nuclei

4. Cytokinesis

a. Animal cells

  • Plasma membrane pinches in along the equator

b. Plant cells

  • Cell plate is laid down across the cell equator
  • Cell membrane forms around each cell & new cell walls form

5. End Result of Mitosis

a. Unicellular organisms

  • Organisms have multiplied community enlarges

b. Multicellular organisms

  • Groups of cells with same function tissue
  • Tissues organize in various combinationsorgans
  • Organs work togetherorgan system

III. Control of the Cell Cycle

1. Enzymes control the cell cycle

a. Each protein/ enzyme is produced by a segment of DNA called a gene.

b. Enzymes are necessary to begin & drive the cell cycle.

c. Enzymes are needed to control cycle through the phases.

2. Mishap with the enzyme production or activity results in loss of control.

a. Cancer is one result of loss of regulation of cell division.

b. Cancerous cells form masses of tissue called tumors.

c. Cancer metastasizes when it has entered the circulatory system to spread.

d. Cancer is the 2nd leading cause of death in USA: lung, colon, breast, & prostate

3. Causes of Cancer

a. Environmental factors: pollution, UV radiation, diet

b. Biotic factors: viral infections, familial genetic mutations

4. Cancer prevention

a. Healthy lifestyle

  • Diet low in fat & high in fiber
  • Diet high in fruits, vegetables, & grains
  • Diet with adequate vitamins & minerals: A, C, & E + Calcium
  • DAILY EXERCISE
  • NO TOBACCO USAGE