Molec and Cell 3 Flashcards
Intracellular signals definition
signals within a cell
Intercellular signals definition
signals between cells
Ligands definition
signals that bind other molecules on target cells
Four categories of signaling
Paracrine
Endocrine
Autocrine
Direct signaling across gap junctions
Paracrine signaling definition
move by diffusion through extracellular matrix
examples include synaptic signals and neurotransmitters
intercellular
Endocrine signaling definition
signals from distant cells, typically produce a slower response with a long-lasting effect
e.g., hormones
intercellular
Autocrine signaling definition
signaling cells that can also bind to the ligand that is released, such that signal and target cell can be the same or similar to each other
e.g., cell death signaling
intracellular
Direct signaling across gap junctions definition
intracellular mediators that allow small signaling molecules to move between cells
intercellular
Internal receptors definition
hydrophobic signaling molecules that typically diffuse across the plasma membrane and interact with intracellular receptors in the cytoplasm
e.g.; DNA and gene expression in nucleus
Cell-Surface Receptors definitions
ligands for these receptors are typically not hydrophobic and would react to the plasma membrane if not for these receptors
might be water soluble or gas
Cell-Surface Receptors Types
Ion channel-linked receptors
G-protein-linked receptors
Enzyme-linked receptors
Ion channel-linked receptors definition
ligands that signal the channel to open or close.
G-protein-linked receptors definition
ligands that bind to these receptors can help regulate many processes
in this case, they help create GTP by hydrolyzing it to GDP, like ATP and ADP
Enzyme-linked receptors definition
ligands help regulate enzymatic activity
e.g.; receptor tyrosine kinase
Receptor tyrosine kinase steps
- ligand binds to enzyme causing it to dimerize
- Tyrosine residues on the back end of enzyme on the intracellular domain are then autophosphorylated, triggering a downstream cellular response
- signal is terminated by a phosphatase that removes the phosphates from the phosphotyrosine residues
Tyrosine kinase function
receptors mediating cell-to-cell communication and controlling a wide range of complex biological functions, including cell growth, motility, differentiation, and metabolism
Signaling molecule definition
Small hydrophobic ligands so they can diffuse directly across the plasma membrane into the cell, where they interact with internal receptors
might be gas or water soluble
steroid hormones have similar chemical structures to their precursor, cholesterol
Three types of signaling molecules
Cholesterol
Testosterone
Estradiol
Propagation of the Signal Types
Signal transduction
Dimerization
Signaling pathway
Signal integration
Signal transduction definition
when a ligand binds to a receptor and the signal is transmitted through the cell membrane and into the cytoplasm continuing the signal
Dimerization definition
two receptors bind to each other to form a stable complex
Signaling pathway definition
chain of events including second messengers, enzymes and activated proteins that follow ligand binding to a receptor
Signal integration definition
signals from two or more different cell-surface receptors merge to activate the same response in the cell
Signaling pathway best example
epidermal growth factor (EGF) receptor (EGFR) is a receptor tyrosine kinase involved in the regulation of cell growth, wound healing, and tissue repair
if EGFR is activated at inappropriate times, uncontrolled cell growth (cancer) may occur
Methods of Intracellular Signaling
Phosphorylation
Second Messengers
Phosphorylation definition for signaling
A phosphate group (PO4-3 ) is added to residues of the amino acids serine, threonine, and tyrosine
Kinase: the enzyme that catalyzes the transfer of a phosphate group
Second Messengers definition for signaling
Small molecules/atoms that propagate a signal
Small and diffuse quickly
Two examples of Second Messengers
cyclical AMP (cAMP)
phospholipase C breaks down PIP2 into IP3 for Ca2+
Response to a signal types
-ERK - MAP kinase that activates translation -Increase in cellular metabolism
-Cell growth
-Cell Death: Apoptosis
ERK Gene Expression signal steps
Hairpin mRNA block!
ERK is a MAP kinase that activates translation when it is phosphorylated.
ERK phosphorylates MNK1, which in turn phosphorylates eIF-4E.
When eIF-4E becomes phosphorylated, the mRNA unfolds, allowing protein synthesis in the nucleus to begin.
Increase in cellular metabolism signal process and proteins
Adrenaline activates β-adrenergic receptors
These increase cyclic AMP (cAMP), which activates PKA.
PKA phosphorylates two enzymes, which lead to a ready supply of glucose and an increase in metabolism
Cell growth signal
Growth factors bind to tyrosine kinases
These initiate a pathway (includeing a G-protein called RAS) which activates MAP kinase pathway
MAP Kinase stimulates protein expression that eventually leads to cell division
Apoptosis signal
Cell signals are terminated by degradation of ligands or by other signals
Ex. Phasphatases: enzymes that remove the phosphate group attached to proteins by kinases
Signaling in Yeasts
Yeast cells can communicate by releasing a signaling molecule called mating factor
Mating factor
Signaling molecule binds to cell-surface receptors in nearby yeast cells.
They stop their normal growth cycles and initiate a cell signaling cascade that includes protein kinases and GTP-binding proteins that are similar to G-proteins.
Key Factor in Bacteria Signaling
Population density
Bacterial signaling name
Quorum sensing
Utilizes molecules called autoinducers
Genome definition
the complete set of genes or genetic material present in a cell or organism
Genome of a prokaryote
one double-stranded, circular DNA molecule
Plasmids in prokaryotes
Additional smaller loops of DNA
Not necessary for normal growth but may have important info
Exchange of plasmids with other cells allows gene transfer in prokaryotes
Genomic DNA in Eukaryotic Cells
Consists of several double-stranded DNA molecules in the form of chromosomes
Chromosomes definition
DNA molecules in the cell that varies between species
chromosome number is consistent, but may vary with developmental stage or specific cell type
Gametes in humans
sperm or eggs that have 23 chromosomes (1 full set)
Somatic cells definition
Non-gamete cells with 2 sets of chromosomes
Ploidy definition
n, 2n, 3n, 4n, etc.
Homologous chromosomes definition
matched pair that are the same length and have specific nucleotide segments called genes in exactly the same location, or locus
One example of heterogenous chromosomes
Sex chromosomes (X, Y)
Sister Chromatids
Replicated homologous chromosomes will have duplicate with centromere binding them
Karyokinesis definition
division of a cell nucleus during mitosis
Cytokinesis definition
the part of the cell division process during which the cytoplasm of a single eukaryotic cell divides into two daughter cells
Type of Positive Regulation of the Cell Cycle
Cyclins and Cyclin-Dependent Kinases (Cdks)
Three Types of Negative Regulation
retinoblastoma protein (Rb), p53, and p21
Oncogenes
Normal genes for positive cell cycle regulators that have mutated
Cyclins and Cyclin-Dependent Kinases (Cdks) function
protein kinases that, when fully activated, can phosphorylate and thus activate other proteins that advance the cell cycle past a checkpoint
Tumors
reproduction of mutated cells surpasses growth of normal cells
begins with a gene mutation that results in a faulty protein that regulates cell reproduction
Proto-oncogenes
normal genes that code for positive cell cycle regulators
Binary fission
asexual reproduction to produce two identical daughter cells
Sexual reproduction
Fusion of gametes (haploid cells) toward the mixing of chromosomes
Asexual reproduction
Cellular division by mitosis or binary fission
Zygote
a diploid cell from two haploid cells
Meiosis definition
the nuclear division of chromosomes resulting in 4 haploid daughter cells
