Unit 4: Transduction Signaling Flashcards
How is the signal transduction pathway activated?
By two cells exchanging mating factors
How do cells communicate with each other?
Via chemical signals
What is a signal transduction pathway?
A series of steps by which a signal on a cell’s surface is converted into a specific cellular response
How do cells in multicellular organisms communicate?
Via chemical messengers
How do animal cells communicate in local signaling?
By direct contact or cell-cell recognition
How do animal cells communicate in long-distance signaling?
By specific chemicals called hormones
The ability of a cell to respond to a signal depends on whether or not it…
Has a receptor specific to that signal
Who discovered signal transduction and how did they discover it?
Earth Sutherland first discovered signal transduction by studying the effects of epinephrine.
Define reception
When a signal molecule, or ligand ,binds to a receptor protein, altering the receptor’s shape.
Define ligands
Highly specific to particular receptors either on cell surface (membrane receptors) or inside of the cell (cynosolic and intracellular receptors)
Are membrane receptors’ ligands polar or nonpolar?
Polar
Are cytosolic receptors’ ligands polar or nonpolar?
Nonpolar
Where are intracellular receptor proteins found?
The cytosol or nucleus of target cells
Which chemical messengers can readily cross the membrane and activate receptors?
Small or hydrophobic chemical messengers
Examples of hydrophobic messengers
Steroids and thyroid hormones of animals
Define a transcription factor
proteins that help turn specific genes “on” or “off” by binding to nearby DNA
An activated hormone-receptor complex can act as a:
Transcription factor
Define a ligand-gated ion channel receptor
Membrane proteins that contain a pore which allows the regulated flow of selected ions across the plasma membrane when receptor changes shape
What causes a ligand-gated ion channel receptor to open?
When a signal molecule binds as a ligand to the receptor
What is the function of protein kinases?
Transfer phosphates from ATP to protein, a process called phosphorylation
What happens at each step of transduction?
The signal is transduced into a different from, usually a shape change in a protein
What is a pathway’s “first messenger”
Small, nonprotein, water-soluble molecules or ions that spread throughout a cell by diffusion.
When does a cell’s response occur?
When cell signaling leads to regulation of transcription or cytoplasmic activities
What are cytoplasmic activities?
Metabolic pathways, ie glycolysis, photosynthesis, and cell division
Do cytoplasmic or nuclear responses usually regulate the activity of enzymes?
Cytoplasmic responses
What do nuclear responses regulate?
The synthesis of enzymes, by turning genes on or off in the nucleus
What is apoptosis?
The death of cells
Signal transduction can alter _______ or cause ________
phenotype; apoptosis
When does apoptosis occur?
During embryonic and fetal development or if a cell is damaged
Explain how apoptosis works:
Components of the cell are chopped up and packaged into vesicles that are digested by scavenger cells
What does apoptosis prevent?
Enzymes from leaking out of a dying cell and damaging neighboring cells.
What are caspases?
The main proteases (enzymes that cut up proteins) that carry out apoptosis
List the triggers of apoptosis
- An extracellular death-signaling ligand
- DNA damage in the nucleus
- Protein misfolding in the endoplasmic reticulum
Define negative feedback
When the product of a reaction leads to a decrease in that reaction
Define positive feedback
When the product of a reaction leads to an increase in that reaction
What is the endocrine system?
A system of glands that secrete chemical signals. Produces a slow, long-lasting response
What is the nervous system?
A system of neurons that transmits electrical signal and releases neurotransmitters to target tissue; fast, short-lasting response
List three uses of hormones
- Chemical messages sent from one part of the body to another
- Communication needed to coordinate the whole body
- Homeostasis and regulation
Define hormones
Chemical messengers produced in low concentrations
A signal hormone can have ___________ _________ on different target cells.
varied effects
Function of endocrine glands
Release their hormones into the bloodstream
Function of exocrine glands
Release their hormones directly to organs via ducts
Peptide hormones
polypeptides (small proteins ie insulin)
glycoproteins (large proteins & carbs)
Steroid hormones
Steroids modified cholesterol
Catecholamine hormones
Modified amino acids ie epinephrine, melatonin
Lipid-based hormones
Hydrophobic and lipid-soluble; Bind to receptor proteins in cytoplasm and nucleus; binds to DNA as transcription factors
Protein-based hormones
Hydrophilic and not lipid-soluble; Can’t diffuse across the membrane; Binds to receptor proteins in the cell membrane; Triggers secondary messenger pathway
What happens in mitosis?
Division of the nucleus
What are the two stages of cell division?
Mitosis and cytokinesis
Before cell division, each chromosome is __________
Replicated
Each chromosome consists of two “sister” _________
Chromatids
M phase
mitosis and cytokinsesis
S phase
chromosome replication or synthesis
Between M and S phases
G1 and G2 (gaps where there are periods of intense growth and activity)
Three stages of interphase
1) G1
2) S phase
3) G2
G1:
cell growth, the cell increases in size, synthesizes new proteins and organelles
S phase:
chromosomes are replicated and the synthesis of DNA molecules takes place
G2:
many of the organelles and molecules required for cell division are produced here, then the cell is ready for the mitotic stages
Prophase
- Chromatin condenses and chromosomes become less visible
- Nuclear envelop dissolves
- Centrioles separate and take up position on either side of the nucleus
What is a centriole and what does it do?
Centrioles are two small structures located in the cytoplasm near the nucleus help separate the chromosomes during cell division
What is a spindle?
A fan-like microtubule structure that forms fibers that attach to and separate chromosomes
Metaphase
- Chromosomes line up across the center of the cell
- Each chromosome is connected to a spindle fiber at its centromere
Anaphase
- Centromeres that join the “sister chromatids split, allowing the chromatids to separate.
- Chromosomes are pulled apart until they have separated into two groups near the poles
Telophase
Chromosomes gather at opposite ends of the cell and lose their distinct shape
- Two new nuclear envelopes form around each set of chromosomes
Cytokinesis (animal cell)
Cell membrane is drawn inward until the cytoplasm is pinched into equal parts. Each part contains its own nucleus and organelles
Cytokinesis (plant cells)
A structure known as a cell plate forms midway between the divided nuclei. The cell plate develops into the cell membrane and a cell wall forms.
Cyclins
Regulate the timing of the cell cycle in eukaryotic cells
Internal regulators
Allow the cell cycle to proceed only when certain process have happened inside the cell
External regulators
Direct cells to speed up or slow down the cell cycle
