Cell Bio

Question 1

Components of intercellular signaling systems

Answer 1

Ligands
Receptors
Secondary Messengers
Signal Transduction
Inactivation methods
Coupling

Question 2

4 major classes of signal transduction networks

Answer 2

1. cascade of protein phosphorylation reactions
2. G-protein coupled reactions
3. Facilitated transport w/ Ach receptors
4. Diffusing across membrane by lipid derivatives

Question 3

Explain Signal transduction involveing a cascade of protein phosphorylation reactions

Answer 3

Protein kinase enzymes can be activated here by phosphorylation

Then later activate downstream kinases

Amplification pathways

Question 4

Explain g-protein coupled reactions

Answer 4

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

Question 5

Explain facilitated transport w/ Ach receptors for signal transduction

Answer 5

Muscle contraction - receptors also acting as channels - responding to Ach in the environment

Question 6

explain signal transduction of lipid derivatives

Answer 6

Estrogen can get into the cell AND into the nucleus no help needed where it bonds to a receptor on the DNA

Question 7

Shared features of sensing/signaling pathways

Answer 7

• 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

Question 8

classic second messenger

Answer 8

cAMP

Question 9

Recognize the central role of protein phosphorylation in signal transduction

Answer 9

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

Question 10

Explain the types of feedback and control mechanisms operative in representative signaling systems

Answer 10

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

Question 11

Plasma membrane refresher

Answer 11

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

Question 12

What is the central dogma of molecular biology

Answer 12

DNA -> RNA -> protein

Question 13

DNA to RNA is called

Answer 13

transcription (nucleotide base-pairing)

-uses RNA polymerase

Question 14

RNA to protein is called

Answer 14

translation (3 nucleotide units code for amino acids)

Question 15

Describe the mechanisms by which information encoded in DNA can be replicated during cell division or accessed during regulated gene expression. (3)

Answer 15

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

Question 16

cell cycle steps

Answer 16

Mitosis -> interphase repeat

interphase = G1 (gap 1) -> S phase (DNA Synthesis) -> G2 (gap 2)

G0 can split from g1 where cells stop dividing

Question 17

Gap 1 of mitosis

Answer 17

growing in size and accumulation of ATP

Question 18

S phase of mitosis

Answer 18

chromosomes are replicated and transcription ceases

Question 19

Gap 2 of mitosis

Answer 19

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

Question 20

Identify the cell death pathways that prevent propagation of damaged chromosomes

Answer 20

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

Question 21

Describe the function of cell cycle checkpoints

Answer 21

Mechanism to maintain genomic integrity
Monitor/surveil for damage and to attempt repair if possible
M-phase checkpoints

Question 22

Describe the requirements for effective repair of errors and the consequences of ineffective repair

Answer 22

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

Question 23

Recognize the types of mechanisms that control progression through the Cell Cycle

Answer 23

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

Question 24

transcription can be activated by …

Answer 24

signal transduction pathways involving ligands and receptors at the surface

Question 25

Steps of mitosis

Answer 25

prophase -> metaphase -> anaphase -> telophase

Question 26

Regulation of gene expression and mitosis (including entry into or progression through the cell cycle) occur by

Answer 26

mechanisms similar to those in other signaling pathways

Amplification cascades involving reversible protein phosphorylation, formation of multi-subunit complexes, negative feedback

Question 27

Transcriptional errors

Answer 27

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

Question 28

M-phase checkpoints

Answer 28

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