Cell Bio Flashcards
Components of intercellular signaling systems
Ligands
Receptors
Secondary Messengers
Signal Transduction
Inactivation methods
Coupling
4 major classes of signal transduction networks
- cascade of protein phosphorylation reactions
- G-protein coupled reactions
- Facilitated transport w/ Ach receptors
- Diffusing across membrane by lipid derivatives
Explain Signal transduction involveing a cascade of protein phosphorylation reactions
Protein kinase enzymes can be activated here by phosphorylation
Then later activate downstream kinases
Amplification pathways
Explain g-protein coupled reactions
Odorant ligands connecting to G Protein Coupled receptor (GPCR) - which connects to a G protein which connects to an enzyme that turns ATP to cAMP (a second messenger) that causes a Na/Ca and Cl gradient channels to open to depolarize the membrane to relay message to the brain
Ligand -> receptor -> protein -> another protein (enzyme) -> channels opening and message being relayed
Hydrolysis of cAMP inactivated pathway
Explain facilitated transport w/ Ach receptors for signal transduction
Muscle contraction - receptors also acting as channels - responding to Ach in the environment
explain signal transduction of lipid derivatives
Estrogen can get into the cell AND into the nucleus no help needed where it bonds to a receptor on the DNA
Shared features of sensing/signaling pathways
• selective recognition of the arriving signal
– formation of a Receptor/Signal complex
• signal amplification
– Production of soluble, intracellular “second messengers”
– Reversible protein phosphorylation as a means of signal transduction
• Appropriate nature and duration of response
– Does the biochemical response fit the biological one?
– Similarities and differences short- vs. long-term responses
• Graded nature of response
– Greater amount/duration of stimulus -» greater magnitude of response
• Mechanisms of control
– Feedback (+/-)
– Desensitization, re-sensitization
classic second messenger
cAMP
Recognize the central role of protein phosphorylation in signal transduction
Phosphorylation is the addition of a phosphoryl (PO3) group to a molecule. In biological systems, this reaction is vital for the cellular storage and transfer of free energy using energy carrier molecules.
Protein phosphorylation is when a channel protein on the membrane of the cell gets a phosphate group from ATP (turning it into ADP)
After the land connects with the receptor it alerts the second messengers which are protein kinases who talk to other protein kinases
Explain the types of feedback and control mechanisms operative in representative signaling systems
Most common is negative feedback
Interconversion of metabolites in a series of enzymatic reactions
Returning the cell back to normal by hydrolysis is a negative feedback mechanism
Plasma membrane refresher
Forms a solubility/permeability barrier
• Opportunity for establishment of concentration gradients
(source of potential energy)
• Site of sensors (receptor proteins) to monitor extracellular environment
• Provides mechanism for selective entry
What is the central dogma of molecular biology
DNA -> RNA -> protein
DNA to RNA is called
transcription (nucleotide base-pairing)
-uses RNA polymerase
RNA to protein is called
translation (3 nucleotide units code for amino acids)
Describe the mechanisms by which information encoded in DNA can be replicated during cell division or accessed during regulated gene expression. (3)
Gene expression can be regulated by transcription factors
-Proteins that bind to DNA promoter regions to prevent/ allow transcription to occur
RNA polymerase - creating RNA polymer from DNA strand during transcription
Through the cell cycle and mitosis
cell cycle steps
Mitosis -> interphase repeat
interphase = G1 (gap 1) -> S phase (DNA Synthesis) -> G2 (gap 2)
G0 can split from g1 where cells stop dividing
Gap 1 of mitosis
growing in size and accumulation of ATP
S phase of mitosis
chromosomes are replicated and transcription ceases
Gap 2 of mitosis
ATP restored to prepare for distribution of chromosomes and organelles
Regulation of interphase is important
Things can go wrong and mechanisms are in place to stop it
Identify the cell death pathways that prevent propagation of damaged chromosomes
Cell death is essential
Response to UV radiation, chemical agents, etc
Orderly dismantling of critical cell survival components
-Seperate from necrosis
-Cell death from disordered lysis- happens during inflammatory responses
Describe the function of cell cycle checkpoints
Mechanism to maintain genomic integrity
Monitor/surveil for damage and to attempt repair if possible
M-phase checkpoints
Describe the requirements for effective repair of errors and the consequences of ineffective repair
DNA damage is detected by sensors (pathways in the nucleus)
Transducer cells communicate with effectors that lead to
-DNA repair
-Cell cycle arrest
-Transcription of damage-responsive genes
-Apoptosis (regulated cell death)
If these mechanisms fail it can lead to persistence of mutations
-Genomic instability
-Birth defects, genetic diseases, notably cancer
Recognize the types of mechanisms that control progression through the Cell Cycle
Landmark phases of the cell cycle are controlled by protein complexes
-Cyclins
-Cyclin-dependent protein kinases (Cdk)
= Both are regulated by phosphorylation interaction
Fidelity and timing of the process are closely monitored
transcription can be activated by …
signal transduction pathways involving ligands and receptors at the surface
Steps of mitosis
prophase -> metaphase -> anaphase -> telophase
Regulation of gene expression and mitosis (including entry into or progression through the cell cycle) occur by
mechanisms similar to those in other signaling pathways
Amplification cascades involving reversible protein phosphorylation, formation of multi-subunit complexes, negative feedback
Transcriptional errors
during transcription gene expression can be altered by timing, magnitude of transcription rate, and the fidelity of base pairing
RNA Polymerase can detect and repair mismatches , but consequences can range if they are not fixed
M-phase checkpoints
certain mutations in proteins controlling m-phase of mitosis can allow it to fail a checkpoint
(causes +/- chromosomes or cancer)
spindle checkpoints
-detect failure of spindle fibers attachment in metaphase
-will trigger apoptosis is damage is not fixed
