Unit 3 Notes

• Cell Junctions—signaling substances in cytosol pass freely between cells o Gap Junctions in Animals o Plasmodesmata in Plants
• Cell-Cell Interaction— interaction between molecules that portrude from cell surface (animals) o Important in embryonic development and immune responses

• Local Regulators—cell secretes a local regulator molecule which acts on specific nearby target cells o Paracrine Signaling—regulators (i.e. growth factors) are released into extracellular fluid) o Synaptic Signaling—neurotransmitters are released into synapse

• Hormones—molecules used in plants and animals for long-distance signaling o Animals = Endocrine Signaling—hormones move through circulatory system o Plants = Plant Growth Regulators—move through vessels or (more commonly) diffuse through cells or air

• Nervous System in Animals—uses a combination of electrical and chemical signals to send a message

Intracellular Signaling
• Three Major Parts— o Reception o Transduction o Response

Reception
• Signaling molecule binds to a receptor protein, causing it to change shape o Ligand—molecule that specifically binds to another molecule (messenger molecule )
• Two Major Types of Receptors o Plasma Membrane Receptors o Intracellular Receptors

Reception
• Plasma Membrane Receptors—transmembrane proteins transmit information into the cell by changing shape or aggregating o G-Protein-Coupled Receptor—works with the help of a G protein. o Receptor Tyrosine Kinases—attach phosphates to tyrosines
(amino acid)…leading to activation of proteins o Ligand-Gated Ion Channels—ligand binds to gated channel protein and opens gate to let in ions, i.e., Na + ,
Ca 2+

Reception
G-Protein-Coupled Receptors

Reception
Tyrosine-Kinase Receptors

Reception

Reception
• Intracellular Receptors—chemical messengers
(small & hydrophobic) enter cell and bind to a receptor in the cytoplasm or nucleus o Testosterone—small steroid hormone
• Activates receptor protein in cytoplasm of target cell by binding to it
• Activated receptor protein (with attached testosterone) enters nucleus and turns on specific genes that control male sex characteristics = transcription factor (proteins that control which genes are on and off)

Intracellular
Receptors
Reception

Transduction
• Cascades of molecular interactions relay signal from receptors to target molecules
• Information is relayed by shape changes of proteins
• Ex: Protein Phosphorylation & Dephosphorylation o Protein Kinases—enzymes that transfer phosphate groups from ATP to a protein (usually activating the protein) o Protein Phosphatases—enzymes that remove phosphate groups from proteins (usually deactivating protein and so turn off pathway)

Transduction

Transduction
• Second Messengers—non-protein, water-soluble molecules or ions that can pass signal to proteins
(1 st Messengers are the original ligands)
• Involved in pathways started by G-protein-linked receptors and receptor tyrosine kinases
• Most common second messengers: o Cyclic AMP (cAMP) o Ca 2+

Transduction
• Cyclic AMP (cAMP) o Adenylyl cyclase converts ATP to cAMP o cAMP activates a protein kinase

Transduction
• Ca 2+ --increase in Ca 2+ leads to many responses in plants and animals o [Ca 2+ ] in blood and extracellular fluid is often 10,000x greater than in cell o Ca 2+ is actively transported out of the cell and into ER o Another molecule, inositol trisphosphate (IP
3
Ca 2+
) stimulates release of

Response
• Cell Signaling leads to regulation of transcription of cytoplasmic pathways o Response may be the regulation of protein synthesis by turning specific genes on or off o Response may be the regulation of a protein’s activity

Response
Cytoplasmic Response
Nuclear Response

Fine-Tuning Responses
• Signal Amplification o Number of activated products increases at each catalytic step of a cascade because enzymes are active long enough to catalyze many reactions o Consequence = small number of ligands can lead to large response
• Specificity of Cell Signaling and Coordination of
Response o Specific types of cells have specific receptors, relay proteins, and/or proteins needed for a response to occur

Fine-Tuning Responses
Signal is unique to different types of cells.

Fine-Tuning Responses
• Scaffolding Proteins & Signaling Complexes o Scaffolding Proteins—large relay proteins that other relay proteins attach to simultaneously o Same proteins can be involved in multiple pathways
• Termination of the Signal o Proteins must be inactivated

Life of a cell from origin through division.

Mitosis and Interphase

Mitosis (M Phase)
• Mitosis—Division of the Nucleus
• Cytokinesis—Division of the cytoplasm
• Mitosis + Cytokinesis = ~10% of Cell Cycle
• Mitosis Phases o Prophase o Metaphase o Anaphase o Telophase

Mitosis (M Phase)
• Mitosis allows cell to go from 4n  2n
• Produces somatic cells
(2n)
• Does not produce gametes (1n)

Interphase
• Interphase—phase in which the cell grows, metabolizes, and copies DNA
• Interphase = ~90% of Cell Cycle
• Split up into 3 smaller phases o Gap 1 Phase (G1)—Takes up ~35% of Interphase
• Growth
• Cell is 2n o Synthesis Phase (S)—Takes up ~35% of Interphase
• DNA Replication occurs
• Cell goes from 2n  4n o Gap 2 Phase (G2)—Takes up ~ 30% of Interphase
• More Growth—Particularly molecules for division
• Cell is 4n

Interphase

Animal Cell

Phases of Mitosis
Summary
• Prophase o Chromatin condenses into chromosomes (made of sister chromatids attached at centromere) o Microtubules form o Centrioles/Centrosomes move to poles

Phases of Mitosis
Summary
• Metaphase o Microtubules attach to the kinetochores of each sister chromatid o Chromosomes line up along the metaphase plate

Phases of Mitosis
Summary
• Anaphase o Sister Chromatids split and move to poles

• Telophase
Phases of Mitosis
Summary o New nuclei form o Microtubules degrade o Cytokinesis occurs

Plant Cell

DNA, Binary Fission & Budding
Objective 14

Bacterial DNA
• One loop of DNA attached to Cell Membrane o Still highly folded to fit into cell o Only one set of genes (not one from “mom” and one from “dad” like in eukaryotes)
• May contain 1 or more Plasmids o Tiny loops of extra DNA that are able to move from 1 bacteria to another o Allows for recombination = advantage!

Binary Fission
• Asexual Reproduction of most Prokaryotes
• Basic Steps: o DNA Replication—unzips to copy o Cell Pinches
• New cells should be clones o No genetic recombination o Only variation through mutations
• Rate = divides as fast as every 20 minutes

Budding
• Some prokaryotes reproduce in this manner—
Asexual Reproduction
• Basic Steps o Cell Develops a bulge or bud o DNA copies o Bud Breaks Off
Listeria monocytogenes

Checkpoints & Regulatory Proteins/Conditions
Objective 12

Check Points
• Between G1 and S o Go ahead signal from the environment is needed (i.e. growth factors from other cells) o Then…there are checks for enough mass and the condition of the DNA o If there is no signal…cell goes to G0 (non-dividing state)
• Most cells in G0 never divide (i.e. nerve/muscle) or they only divide if there is an injury
• Between G2 and M o Checks for mass and correct DNA replication o If all okay…cell commits to divide
• Note: Cancer often occurs because cell is quickly pushed from G1  S without proper checks

Regulatory
Molecules/Conditions
• Regulatory Proteins/Enzymes o Cyclin-Dependent Kinase (Cdk)—enzymes needed to drive the cell cycle
• Cyclin-Dependent Kinase (enzyme that activates or deactivates other molecules by phosphorylation) only works when activated by cyclin— a protein that rises and falls in the cell cycle o Example: Maturation Promoting Factor (MPF)—
• Cyclin increase in concentration in G2 and bind with a specific Cdk to form MPF
• MPF signals the start of Mitosis
• At end of mitosis, enzymes break down cyclin…so no MPF…and no more dividing (Cdk concentration remains the same)

Regulatory
Molecules/Conditions

Regulatory
Molecules/Conditions
• Other internal signals o Kinetochores must be attached before anaphase can occur— unattached kinetochores send a signal to stop sister chromatids from splitting

Regulatory
Molecules/Conditions
• External Signals o Growth Factors—proteins released by certain cells that stimulates other cells to divide o Density-Dependent Inhibition—Crowded cells stop dividing because there aren’t enough growth factors and nutrients for it to divide o Anchorage-Dependence—If cells aren’t attached to the extracellular matrix, they do not get growth factors—so don’t divide

Objective 13—Define cancer and explain how aberrations in the cell cycle can lead to tumor formation.

Cancer
• Complex collection of diseases that can arise in almost any tissue in the body.
• All cancers arise as a result of the loss of cell cycle control.
Cytotoxic T Cell Attacking a
Cancer Cell

Cancer Cell
Characteristics
• Uncontrolled growth
• Lack of response to stop signals
• Immortality
• Ability to divide infinitely
• Recruits food supplies (angiogenesis)
• Random migration

Cancer Cell
Characteristics

Benign versus Malignant
Benign (not cancer) tumor cells grow only locally and cannot spread by
Malignant (cancer) cells invade neighboring tissues, enter blood vessels, and metastasize to different only locally and cannot spread by invasion or metastasis

Cancer-Related Genes
• Stability Genes—code for proteins that keep genetic alterations to a minimum o If mutated, mutation rates increase
• Oncogenes—code for proteins that promote cell division o If mutated to be overly active = cancer
• Tumor Suppressor Genes—code for proteins that inhibit cell from progressing from G1  S o If mutated to be underactive = cancer o Example TP53 codes for p53 protein = transcription factor that normally inhibits cell growth and stimulates cell death when induced by cellular stress

Check Points