Chapter 3 The Cellular Level of Organization

Cell Theory

1. Cells are building blocks of all plants

2. All new cells come from division of preexisting cells

3. Cells are smallest living units that perform all vital physicolgical functions

4. Cells are the smallest living units of life

Extracellular fluid

cells surrounded by watery medium

Cytosol (Intracellular fluid)

Fluid inside cell (fluid part of cytoplasm)

Plasma membrane

What seperates cell contents (cytoplasm) from extracellualr fluid

Organelles

intercellular structures with specific functions

Non-membranous

• Not completely enclosed by membranes

• In direct contact with cytosol

• Cytoskeleton, cilia, flagelia, centrolies, microvilli, ribosomes

Membranous

• Enclosed in a phospholipid membrane

• Isolated from cytosol

• mitochodria, nucleus, endoplamsic reticulum, golgi apparatus, lysosomes, perxisomes

Peroxisome

Structure:

• Vesticles containing degradative enzymes

Function:

• Break down organic compounds

• Neutralize toxic compounds

Lysosome

Structure:

• Vesicles containing digestive enzymes

Function:

• Break down organic compounds and damaged organelles or pathogens

Mitochondrion

Structure:

• Double membrane

• Inner membrane contains metabolic enzymes

Function:

• produces 95% of cellular ATP

Cytoskeleton

Structure:

• Proteins organized into fine filaments or slender tubes

• Centrosome- organizing center containg pair of centrioles

Function:

• Stregthens and supports cell

• Moves cellular structures and materials within cell

Integral proteins

• part of cell membrane and cannot be removed without damaging cell

• Often span entire cell membrance (also called transmembrane proteins)

• can transport water or solutes

Peripheral proteins

• attached to cell membrane inner or outer surface

• Easily removable

• fewer than integral proteins

• May have regulatory or enzymatic functions

Cytoskeleton 2

• functions as cell’s skeleton

• provides internal protein framework

• gives cytoplasm stregth and flexibility

Ribsomes

• Responsible for protein synthesis

• Two subunits (1 large, 1 small) containing special proteins and ribosomal RNA (rRNA) must join together before synthesis begins

Free ribosomes

• throughout cytoplasm

• manufactures proteins enter cytosol

Bound or fixed ribosomes

• attached to rough endoplasmic reticulum

• synthesize proteins for export out of cell

Endoplasmic Reticulum

• Network of intracellular membranes continous with nuclear envelope, which surrounds nucleus

• Forms hollow tubes, sheets, and chambers (cisternae, singular, cisterna, resvoir for water)

• Synthesizes and stores proteins, lipids, and carbohydrates

Smooth Endoplasmic Reticulum (SER)

• Lacks ribosomes

• Cisternar are often tubular

Rough Endoplasmic Reticulum

• Has attached (fixed) ribosomes

• Modifies newly synthesized proteins

• exports those proteins to Golgi apparatus

Golgi Apparatus (Golgi complex)

• Renews or modifies plasma membrane

• Modifies or pacjages secretions into secretory vesicles for release from cell (exocytosis)

• Packages special enzymes within vesicles for use in cytosol (lysosomes)

• Situated near nucleus

Mitochondria

• produces energy (ATP) for cells

• Vary in number per cell depending on cell’s energy requirments (more enrgy needs = more mitochondria)

• Contain their own DNA (mtDNA) and ribosomes

ATP Production

1. Glycolysis

   • Occurs in cytosol

   • 1 glucose —> 2 pyruvate

   • Pyrvate absorbed into mitochindria

2. In mitochondrial matrix:

   • CO2 removed from pyruvate

   • Enters citruc acid (TCA, tricarboxylic acid) cycle

3. Enzymes and coenzymes use hydrogen atoms to catalyze ATP from ADP (also forms H2O)

4. ATP leaves mitochondrion

Cellular Respiration or Aerobic metabolism

• ATP production that requires oxygen

• Occurs in the mitochondria

• Much more effecient than ATP production without oxygen

• Produces about 95% of ATP needed by cell; remaining 5% produced by enzymatic reactions in the cytoplasm

Nucleus

• Usually largest cellular structure

• Control center of cellular operations

• Genetic information coded in dequenceb of nucleotides

• Determines cell structure and fucntion

Nuclear envelope

• sepreates nucleus from cytoplasm

• Double mebrane

• Perinuclear space; space between layers

Nuclear pores

Passageways that allow chemical communication between nucleus and cytoplasm

Nucleoplasm

• fluid contents of nucleus

• contains network of fine filaments for structural support

• Also contains ions, enzymes, nucleotides, and small amounts of RNA and DNA

DNA in the Nucleus

• Stores instructions for protein synthesis

• strands in nucleus coiled, allowing much to be packed in small space

• wrap around histone molecules forming nucleosomes

• Loosley coiled (chromatin) in nondividing cells

• Tighly coiled (chromsomes) in divinding cells

DNA

• Long parallel chains of nucleotides

• Chains held by hydrogen bonds between nitrogenous bases

• Four nitrogenous bases: Adenine, Thymine, Cytosine, Guanine

• Genetic information sequence of base pairs; known as the genetic code

Triplet code

• Sequence of three nitrigenous bases

• Specifices single amino acid

Gene

• Functional unit of herdity

• Contains all the DNA nucleotides to produce a specific protein

• Size varies

Protein Synthsis

1. Gene Activation: removal of histones and DNA uncoiling

2. DNA strands seperate

3. Enzymes assemble nucleotides into a single strand of messenger RNA (mRNA). Complemetary base pairing matches DNA to mRNA (A-U; G-C)

4. mRNA leaves nucleus through nuclear pores

5. At a ribosome in the cytoplasm, codons of mRNA bind to anticodons on transfer RNA (tRNA)

6. tRNA carries specific amino acid

7. Ribosomal RNA (rRNA) of the ribsome strings amino acids together

Permeability

Property determining which substances can enter or leave

• Free Permeable: any substance can pass (not found in living cells)

• Selectively permeable: some substances cross

• Impermeable: No substances can pass (not found in living cells)

Passive membrane transport

• does not require ATP

• Diffusion

• Cariier-mediated transport

Active membrane transport

• Requires ATP

• Vesicular Transort

• Carrier-mediated transport

Diffusion

• net movemen of substrance from higher concentration to lower concentration

• At an even distribution, molecular motion continues but no net movement

• slow in air and water but important over small distances

• Concentration Gradient: concentration difference when molecule are not evenly distributed

Factors that influence diffusion rate

• Distance

  • Shorter distance = faster diffusion

• Molecule or ion size

  • smaller size = faster diffusion

• temperature

  • higher temperature = faster diffusion

• Concentration Gradient

  • Steeper gradient = faster diffusion

• electrical forces

  • attraction of opposite charges (+,-)

  • Repulsion of like charges (+,+ or -,-)

Osmosis

The diffusion of water across the cell membrane

• More solute molecules, lower concentration of water molecules

• Membrane must be freely permeable to water, seletively permeable to solutes

• Water molecules diffuse across membrane toweard soilution with more solutes

Osmotic Pressure

Indication of force of pure water moving into a solution with higher solute concentration

Osmolarity (osmotic concentration)

Total solute concentration in an aqueuos solution

Tonicity

• effect of somotic solution on cell volume

• How a solution affects a cell

Isotonic

Solution that does not cause osmotic flow across membrane

Hypotonic

• causes osmotic flow into cell

• Swelling and hemolysis

• has more water than solute

• water moves into cell

Hypertonic

• causes osmotic flow out of cell

• Shriveling and crenation

• has more solute than water

• water moves out of cell

Active Trasnport

• active process requiring energy molecule or ATP

• Independent of concentration gradient

Vescular Transport

Materials move across cell membrance in small membranous sacs called vesicles, sacs form at or fuse with plasma membrane; carry material in and out of cell

Endocytosis

importing extracellular substances into vesicles called endosomes

Exocytosis

exporting watses or secretory prpducts from intrcellular vesicles to outside the cell

Mitosis

• 2 daughter cells produced

• each with 46 chromosomes

• divides genetic material equally

Meiosis

• produces sex cells

• each with only 23 chromosomes

DNA Replication

duplicates genetic material exactly

Cytokinesis

divides cytoplasm and organelles into two daughter cells

DNA Polymerase

1. Promotes bonding between the nitrogenous bases of the DNA strand and complementary DNA nucleotides dissolved in the nucleoplasm

2. Links the nucleotides by covelant bonds

Ligases piece together sections of DNA