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Explain the composition and role of the animal’s extra cellular matrix.
- Structural support, much protein
- Fibrous component of animal ECM is dominated by a cable-like protein
- Matrix that surrounds collagen and the other fibrous components consists of gel-forming polysaccharides-most attached to protein core
- Structure correlates to cells function
- Direct linkage between cytoskeleton and ECM is critical. Keep cells in place and helps adjacent cells adhere to each other via their common connection to the ECM
Explain how plant cells are attached and communicate with each other.
- Connections called plasmodesmata – physical connection between two plant cells, consisting of gaps in the cell walls through which the two cells’ plasma membranes, cytoplasm, and smooth ER can connect directly.
- Plasma membrane cytoplasm continuous, smooth ER runs through the holes
What role do hormones play in multicellular communication?
- Hormones deliver their message by binding to receptor molecules.
- Presence of appropriate receptor dictates which cells will respond to a particular hormone
- Trigger large response
- Arrives at cell surface, message it transmits amplified as it changes form.
What is signal transduction (explain to Grandma)?
- Signal binds at the cell surface, converted from one form to another, to intracellular signal.
- Plasma membrane, amplification inside,
Explain how G proteins receptors and receptor tyrosine kinases accomplish signal transduction.
- G proteins activated by a signal receptor, trigger key step in signal transduction (production of a messenger inside the cell). Link the receipt of an extracellular signal to the production of an intracellular signal.
- Bind GTP and GDP
- Hormone arrives and binds to receptor in the plasma membrane. Receptor is transmembrane protein, coupled to peripheral g protein on membranes inner surgace, receptor changes shape after hormone binding
- Shape change is a witch that activates its g protein. Releases gdp molecule that kept it in an inactive state and binds GTP. GTP attached, G protein changes shape radically, splits into 2 parts.
- One part of g protein activates nearby enzyme that is embedded in the plasma membrane. Enzyme catalyzes production of a second messenger( nonprotein signaling molecule that elicits a reponse to the first messenger)
- Instead of activating g protein, enzyme linked receptors transduce signal from hormone by directly catalyzing a reaction inside the cell.
- Hormone binds to an RTK
- Protein forms a dimmer. Receptor has a binding site for a phosphate group from ATP inside the cell. Once it is phosphorylated, RTK becomes an active enzyme
- Proteins inseide the cell form a bridge between the activated RTK and a peripheral membrane protein called Ras, functions like a G protein. Formation of the RTK bridge activated Ras, echanges GDP for GTP
- Ras activated, triggers the phosphorylation and activation of another proteiin.
- Phosphylated protein then catalyzes the phosphorylation of other proteins, which phosphorylate yet another population of proteins
Explain the four phases of the eukaryotic cell cycle.
M phase, interphase consisting of the G1, S, and G2 phases
G1 phase –
phase of cell cycle that constitutes first part of interphase before DNA synthesis (s)
S phase –
synthesis phase, DNA synthesized and chromsomes are replicated
G2 phase –
phase of cell cycle between synthesis of DNA (s phase) and mitosis (M phase), last part of interphase
M phase –
chromosomes condense into compact structures, spindle apparatus begins to form
nuclear envelope breaks down. Kinetochore microtubules contact chromosomes at kinetochore
chromosomes complete migration to middle of cell
sister chromatids separate. Chromosomes pulled to opposite poles of the cell
nuclear envelope re-forms, and spindle apparatus disintegrates
Explain the difference between mitosis and cytokinesis.
- before m phase, mitochondria, lysosomes, chloroplasts, and other organelles have replicated, rest of cell contents grown.
- During cytokinesis, cytoplasm divides to form two daughter cells, each with its own nucleus and complete set of organelles. Mitosis is followed by cytokinesis.
- Plasma membrane begins pinching in, becomes two daughter cells to form
Describe the various ways the cell cycle is controlled.
depends on sufficient nutrients, cell size, lack of DNA damage, and/or social signals
delays progress until chromosome replication is complete and any damaged DNA that is present is repaired
M phase checkpoint
- delays anaphase until all chromosomes are correctly attached to the spindle apparatus
- Cyclins and cyclin-dependent kinases (cdks)
- help regulate the cell cycle. Cyclinconcentrations oscillate during the cell cycle, regulating the activity of Cdks. Active Cdks phosphorylate proteins required for the nect cell cycle phase
Explain the consequences of uncontrolled cell division.
- Uncontrolled cell division may lead to cancer
- Cancer is characterized by (1) loss of control at the G1 checkpoint, resulting in cells that divide in an uncontrolled fashion, and (2) metastasis, or the ability of tumor cells to spread throughout the body
- G1 checkpoint depends in part on Rb, which prevents progression to S phase, and G1 cyclin-cdk complexes that trigger progression to s phase. Defects in Rb and G1 cyclin are common in human cancer cells