Unit 3 Review Cell Division Cell Signaling Binary

Unit 3 Review Cell Division & Cell Signaling

Binary Fission • Reproduction in prokaryotes • DNA replication occurs making a copy of the single, circular chromosome • Produces clones • Would have evolved into mitosis

Binary Fission in Prokaryotes Cell wall Origin of replication E. coli cell Chromosome replication begins. Soon thereafter, one copy of the origin moves rapidly toward the other end of the cell. Replication continues. One copy of the origin is now at each end of the cell. Replication finishes. The plasma membrane grows inward, and new cell wall is deposited. Two daughter cells result. Two copies of origin Origin Plasma membrane Bacterial chromosome Origin

Genome • The ENTIRE genetic material (DNA) for an organism or cell

Somatic vs. Germ • Somatic cell – Normal body cells – 2 n or diploid – Humans 2 n = 46 chromosomes • Germ cell – Means beginning – Will undergo meiosis to become haploid sex cells – Become gametes (eggs or sperm) • n or haploid • Humans n = 23 chromosomes

Somatic cells vs. Germ cells The egg surrounded by sperm.

Chromatin vs. Chromosome • Chromatin – the LOOSE state of DNA • Chromosomes – the HIGHLY COILED state of DNA – For dividing equally and easily during cell division

Chromatin vs. Chromosomes appearance within the cell.

Histones • Proteins that help DNA coil up “condense” to form the chromosomes needed for division

Coiling up of Chromatin using histones

Sister Chromatids • A portion of the whole “duplicated chromosome • Half of a duplicated chromosome. Duplicated chromosomes look like an “X” • The two halves are held together at the centromere

Sister Chromatids

Mitosis vs. Meiosis (Eukaryote Cell Division) • Mitosis – Ordinary cell division – Parent and daughter cells are identical genetically – ONE division • Meiosis – The process of forming haploid gametes – Have half the genetic material as the parent cell – NOT genetically identical to each other or the parent – TWO divisions

Interphase • 90% of cell existence • Three parts: – G 1 (primary or “first” growth”) • Ordinary, everyday growth, activity or repair of the cell • Organelles begin replicating • First checkpoint (“Point of no return”) – S (synthesis) • DNA replicates – G 2 (Secondary or “second” growth) • Organelles enlarge or complete replication • DNA is checked for errors • Second checkpoint occurs after this point (Have everything for 2 cells? )

Interphase

Before and after the S phase

Mitosis • PMAT • Cytokinesis – Division of the cytoplasm • G 0 – (Zero growth phase) – Cells are tired and take a brief break and rest or they stop adult development

Start of Mitosis

Mitosis “Division of the nucleus”

Spindle Apparatus • Formed from broken down cytoskeleton and nuclear envelope • Attach to the KINETOCHORE on the centromere of the replicated chromosomes

Motor Protein and the Spindle Fibers Chromosome movement Microtubule Motor protein Chromosome Kinetochore Tubulin subunits

Regulation “control” of the Cell Cycle • Crucial for normal growth and development • Controlled by proteins called CYCLINS (must combine with c. Dk, cyclin dependent kinase, to become active) • Three checkpoints – G 1 – Point of no return – End of G 2 – Do we have everything needed for 2 cells? – End of Metaphase – Are all the chromosomes attached and lined up and ready to divide/separate or segregate? (Kinetochore signal occurs here to signal Anaphase to begin)

. 1 G Cyclin is degraded M Degraded cyclin G 2 checkpoint MPF Cdk in accumulation Cycl S Cdk Cyclin Molecular mechanisms that help regulate the cell cycle

Relative concentration . M G 1 S G 2 M MPF activity Cyclin Time Fluctuation of MPF activity and cyclin concentration during the cell cycle

Checkpoints (Is all going according to plan? )

Theta Chromosome (Prokaryotic) vs. Eukaryotic chromsomes • More genes on Eukaryotic – More variation – More possible genetic combinations to inherit • More genetic stability on Eukaryotic – Offspring receive same # of chromosomes (typically) – Important linked genes tend to be inherited together • Eukaryotic allows for diploid cells to exist, as a result of sexual reproduction and one half o the DNA to come from each parent – Increase variation

Density-dependent Inhibition • A cell STOPS diving when CONTACT is made with other cells

Anchorage Dependence • Cells must be connected to the connective tissue base to divide

. Cells anchor to dish surface and divide (anchorage dependence). When cells have formed a complete single layer, they stop dividing (density-dependent inhibition). If some cells are scraped away, the remaining cells divide to fill the gap and then stop (density-dependent inhibition). Normal mammalian cells 25 µm

. Cancer cells do not exhibit anchorage dependence or density-dependent inhibition. 25 µm Cancer cells

Metastasis • Movement of cancer cells from the site of origin to another site within the body

Cancer Genes • RAS gene – 30 % of all cancers are result of this mutation – G-protein is mutated. These are involved in normal cell to cell communication. A faulty signal transduction pathway occurs. – The cell CANNOT shutdown the signal to grow going to the nucleus; so it reproduces very quickly and constantly • p 53 gene – 50% of all cancers are result of this mutation – A cell cannot commit suicide when it becomes damaged beyond repair. Prevents cell cycle shutdown because Cyclin becomes constantly produced by the damaged cell leading to more defective cells being produced.

Mutations and Cancer MUTATION Growth factor Hyperactive Ras protein (product of oncogene) issues signals on its own G protein Cell cycle-stimulating pathway Receptor Protein kinases (phosphorylation cascade) NUCLEUS Transcription factor (activator) DNA Gene expression Protein that stimulates the cell cycle Cell cycle-inhibiting pathway Protein kinases UV light DNA damage in genome Active form of p 53 DNA Protein that inhibits the cell cycle MUTATION Defective or missing transcription factor, such as p 53, cannot activate transcription

Cell Communication • Direct Signaling – physical contact • Local Signaling – Growth factors released into a localized area – At the synapses of neurons • Long Distance Signaling – Hormones – Pheromones

Direct Contact

Local and Long Distance within an organism.

Phermones

Signal Transduction Pathway • Reception – the ligand binds to the membrane receptor protein on the cell membrane or inside the cell causing a conformational shape change • Transduction – changes the signal to something the cell can understand at the nucleus or in the cytoplasm/amplifies the message • Response – making something or turning on/off an enzymatic process (usually involves DNA transcription and translation or enzymes INSIDE the cell)

Step 3: Response

See the CONFORMATION SHAPE CHANGE by the receptor protein caused by the ligand binding. Signal molecule (ligand) Gate closed Ligand-gated ion channel receptor Ions Plasma membrane Gate open Cellular response Gate closed

Important Receptor Protein Pathways in Cells • G-Protein Linked Receptor – serves as the attachment point for the LIGAND – found in the plasma membrane of a cell – Will change shape upon attachment of the proper ligand – ALL cells possess these allowing them to interact with and respond to the environment around them • Tyrosine-Kinase Pathway – involved with growth/emergency repair most of the time

G protein Receptor

Tyrosine – Kinase Receptor

Important Receptor Protein Pathways in Cells • Ion Channel Receptors (found at synapses of neurons) – Ligand-gated Ion Channels – Act as CONTROL of a particular signal – The gate is opened by attaching the neurotransmitter (the ligand) to the receptor protein. Then, the charged sodium ions can enter the cell to start depolarizing that cell. • INTRAcellular Receptors – Mostly for receiving hormones and steroids – Since they are lipids they don’t need receptor proteins on the cell membrane – Travel in by diffusion

Ion Channel Receptors Signal molecule (ligand) Gate closed Ligand-gated ion channel receptor Ions Plasma membrane Gate open Cellular response Gate closed

Intracellular receptors

Secondary Messengers • Relay molecules within the cell’s cytoplasm

First messenger (signal molecule such as epinephrine) Adenylyl cyclase G protein G-protein-linked receptor GTP ATP c. AMP Second messenger Protein kinase A Cellular responses

Secondary Messenger Calmodulin EXTRACELLULAR FLUID Signal molecule (first messenger) G protein DAG GTP G-protein-linked receptor Phospholipase C PIP 2 IP 3 (second messenger) IP 3 -gated calcium channel Endoplasmic reticulum (ER) CYTOSOL Ca 2+ (second messenger) Various proteins activated Cellular responses

Signal Amplification • Protein Kinase Cascades – Kinases turn ON processes by phosphorylating the molecule – Cascade amplifies the signal – Each step in the cascade can amplify a signal – Also can control the reaction rate of the process • Protein Phosphotase Cascades – Turn OFF processes by removing a phosphate ion from the molecule • Amplification of the Signal – Only need a small amount of the ligand to convey the message (conserves energy and materials) – Cascades amplify the signal at each step

Kinases “turn on” processes Phosphotases “turn off” processes

Small signal produces a BIG response

The Big picture Growth factor Reception Receptor Phosphorylation cascade Transduction CYTOPLASM Inactive transcription factor Active transcription factor P Response DNA Gene NUCLEUS m. RNA

Scaffolding Proteins • Allows for direct contact stimulation of multiple relay proteins at one time

Scaffolding Proteins Signal molecule Plasma membrane Receptor Three different protein kinases Scaffolding protein

Tyrosine – Kinase Receptor (Evolution – Change over TIME)