The Cell

Chapter 3

Cell Diversity

Cell Theory

• All living things are composed of cells

• Cells are the smallest unit to demonstrate the properties of life

• Cells are only produced from existing cells

Typical Animal Cell• Plasma membrane– Outer limiting barrier– Detect chemical signals and recognize self from

non-self

• Nucleus– Control center

• Cytoplasm (cytosol)– Intracellular fluid

including organelles (excluding)

Plasma Membrane’s Role • Physical isolation

– Separates intracellular from extracellular environment

• Regulates exchange with environment– Selective permeability

• Polarity (hydrophobic vs. hydrophilic)• Charge (charged vs. uncharged)• Size (large vs. small)

– Ions & nutrient enter, wastes & secretions exit– Allows a concentration gradient to develop

• Maintains homeostasis

The Fluid Mosaic Model• Integral proteins– Channels, carriers, and signal transduction

• Peripheral proteins– Enzymes, cell-cell recognition, and structure

• Phospholipid bilayer (unsaturated)– Hydrophilic ends– Hydrophobic ends

• Cholesterol

Types of TransportPassive• Energy not required• Movement ‘down’ a

concentration gradient• Specific types

– Diffusion• Simple• Facilitated

– Osmosis– Filtration

Active• Energy required• Movement against a

concentration gradient

Clarifying Solutions

• Liquid mix of 2+ substances– Aqueous solution when water is

solvent• Solvent: dissolving agent• Solute: substance that is dissolved• Reviewing polarity– ‘Like dissolves like’– Hydrophilic

• Sugar or salt and water– Hydrophobic

• Oil and water

Simple Diffusion• Movement of MOLECULES ‘down’ their

concentration gradient– Small, nonpolar molecules

• E.g. O2 in and CO2 out in red blood cells– Each substance is independent

• Continues until equilibrium = no NET movement

Osmosis• Movement of WATER ‘down’ its concentration

gradient– Water binds to solute in solution

• More solute = less free water = less water available to move• Depends on TOTAL solute concentration– Selective permeability has a role too

watermolecules

glucosemolecules

Tonicity• Ability of a solution to cause a cell to gain or lose water

– Depends on [solutes] that can’t cross PM relative to those in the cell• Hypotonic solutions have a ___?__ [solute] than the cell

– Water moves in – Cells lyse

• Hypertonic solutions have a ___?__ [solute] than the cell– Water moves out

• Cells crenate• Isotonic solutions have ___?__ [solute] as the cell

– Water shows no NET movement

Other Passive Transport Types

Facilitated diffusion• Movement same as simple• Larger, water soluble

substances– Glucose, water, & ions

• Protein carriers or channels

Filtration• Water and solutes move

‘down’ a pressure gradient– Water forced, solutes chosen

by size

• Bulk movement

Active Transport• Movement of MOLECULES against their

concentration gradient• ATP is energy source• Maintains disequilibrium

Vesicular Transport• Exocytosis: removes

from inside the cell– Golgi vesicles to PM

• Endocytosis: brings into the cell– PM pinches in to form

vesicles– 3 types

• Phagocytosis• Pinocytosis• Receptor-mediated

Plasma Membrane Specializations• Microvilli– Folds of PM to increase surface area

• Membrane Junctions– Tight junctions

• Integral proteins = impermeable• E.g. keep digestive enzymes out of blood

– Desmosomes• Protein filaments = high tension protection• E.g. skin and heart muscle

– Gap junctions• Integral proteins for communication• E.g. heart and smooth muscle

Nucleus

• Control center of the cell• Nuclear envelope

– Double membrane continuous with rough ER

– Maintains shape– Nuclear pores for transport; selectively

permeable• Nucleoli

– Build ribosome subunits• Chromatin

– DNA and protein– Coils/condenses to become visible =

chromosomes

Organelles Within Cytosol

Membranous• Mitochondria

– Produces ATP• Endoplasmic reticulum (ER)

– Rough – proteins to Golgi– Smooth – lipids & carb

production; detoxification• Golgi apparatus

– Modify and package secretory vesicles

• Lysosomes– Digestive processes

• Peroxisomes– Detoxification

Nonmembranous• Cytoskeleton

– Microtubules, microfilaments, & intermediate filaments

• Centrioles– Formed by microtubules, 9

triplets– Microtubules originate in

mitosis• Ribosomes

– Small and large subunits– Free or attached = dynamic

• Cilia– Move substances or organism

• Flagella– 9 + 2 orientation

The Cell Cycle (IPMATC) • Interphase about 90%

– Chromosomes not visible yet– G1 phase– S phase– G2 phase

• Mitotic (M phase) cell division– Mitosis is nuclear division

• Prophase• Metaphase• Anaphase• Telophase

– Cytokinesis is cytoplasmic division• Repeat as needed

DNA Replication• Helicase– 2 templates formed

• DNA polymerase– Complementary base pairing

• Daughter strands– Leading strand– Lagging strand

• DNA ligase

• Semiconservative model– Chromatid sister chromatids

Prophase Events

• Sister chromatids condense

• Nuclear envelope begins to disappear

• Centrioles appear at opposite ends of cell

• Mitotic spindles form

Metaphase Events

• Centrioles at opposite ends of cells

• Sister chromatids line up with centromere on metaphase plate

• Microtubules attached to each chromatid at the centromere

Anaphase Events

• Sister chromatids separate

• Single chromosomes move toward opposite ends of the cell– Microtubule ‘tug of war’

• Cell elongates

Telophase Events

• Daughter nuclei form

• Nuclear envelope reforms

• Chromosomes begin to uncoil

• Mitosis is complete

Cytokinesis

• Division of cytoplasm– Begins at the end of telophase (late

anaphase too)

• Cleavage furrow forms– Pinch plasma membrane in 2

• 2 identical daughter cells formed

Meiosis

• Similar to mitosis• Reduces genetic material of each daughter cell by

half– Diploid (2n) adult produces haploid (n) gametes

• n = # different chromosomes, paired = homologous• Autosomes (22) and sex chromosome (X or Y)

• Event occurs in 2 cycles– Meiosis I

• Most variation from mitosis– Meiosis II

Protein Synthesis• DNA RNA protein– Genes instruct, but don’t build– Nucleotides and amino acids are

different ‘languages’– RNA connects them

• Transcription: same language• Translation: different language

Reviewing DNA and RNA

DNA• Sugar is deoxyribose

– Has –H

• Bases are A,C, G, and T• Double-stranded helix• Only in nucleus• Modified only by mutations• 1 type

RNA• Sugar is ribose

– Has -OH

• Bases are A, C, G, and U• Single-stranded• Not confined to nucleus• Lots of processing and

modifications• 3 types (mRNA, tRNA, rRNA)

Transcription• Only 1 template used• RNA polymerase

– Complementary bases added• Steps

– Promotion– Elongation – Termination

• Pre-mRNA processing– Introns spliced out– Exons rejoined– mRNA

Decoding Genes • 4 nucleotide bases to

specify 20 amino acids• Based on codons– 43 = 64 (plenty)

• Redundancy, but not ambiguity

• Nearly universal across species

Translation• Ribosome binds mRNA

– In cytoplasm• tRNA with anticodon binds

– Start codon to P site– 2nd tRNA to A site– Peptide bond joins AA’s

• Ribosome translocates– P site with 1st & 2nd AA– New tRNA to A site

• Stop codon terminates– Polypeptide folds = protein

Summary of Protein Synthesis