Week 4: cell comms + enzymes Flashcards
What determines the ability of a cell to respond to a signal?
A cell needs a specifc receptor to respond to a given signal. If it contains this specific receptor it is known as the target cell
What does a receptor do?
A receptor can bond to chemical ligands or respond to physical stimulation such as light.
(Ligand = the molecule that bonds to receptor).
What are the two key types of receptor based on location?
Receptors can be intracellular (on the inner plasma membranes e.g. in nuclear envelope, cytoplasm) or extracellular (on outer plasma membrane.
How does the nature of the signal determine the sort of receptor needed?
If the signal can enter the cell (e.g. is non polar) then an intracellular receptor can be used, but if the signal can’t enter the cell (e.g. is polar) then an extracellular receptor is necessary.
What are binding sites?
Binding sites are specific areas of the receptor which are shaped to fit the specific ligand.
Drugs like caffeine can bind to receptors and block out the things that are meant to bind to them e.g. caffeine binds to adenosine receptor to block out adenosine.
What are the three key types of receptor?
The three key types of signal are
- Autocrine
- Juxtacrine
- Paracrine
(Autocrine = binds to receptors on the same cell which secretes it) (Juxtacrine = affects only adjacent cells: common in early tissue development) (Paracrine = affect nearby adjacent AND non-adjacent cells e.g. skin cells signal to blood cells in wound response).
How are plants and animals different in terms of communication methods between adjacent cells?
Animal cells = have gap junctions
Plant cells = have plasmodesmata
Both are effectively a channel through which molecules and ions can pass.
How is long-distance cell to cell communication achieved?
When signals have to travel a long distance in the body this is achieved using hormones: signals that travel through the circulatory/vascular system to distant receptors.
in both plants and animals.
What is a signal transduction pathway and how does it relate to reception and response?
A signal transduction pathway describes the response/outcome of a receptor to binding to a signalling molecule.
–> The chain of events that lead to a cellular response
Three phases:
1) Reception (signal binds to receptor)
2) Transduction (changes occur through a signal transduction pathway)
3) Response (activation of cellular response)
How can signals affect receptors to signal changes in a signal transduction pathway?
Some receptors change shape (conformation) and/or activity (e.g. to expose active site) after binding to ligands and this change triggers stimulus response in signal transduction pathway.
What is the role of the signal transduction pathway?
The signal transduction pathway is a cascade of interacting proteins + various mechanisms that TRANSMITS AND AMPLIFIES a signal inside a cell. Can be simple and short or long and complex.
- Signal starts off affecting 1 molecule, ends up affecting 100s.
What is the role of kinase?
Kinase is an enzyme that catalyses the transfer of phosphase groups from ATP to a subtrate (ATP => ADP)
What triggers a phosphorylation cascade and what is its effect?
Recognition of a signal triggers a phosphorylation cascade.
This induces a series of protein kinases that activate each other in sequence, amplifying the signal at each step.
-> Activating kinase allows phosphate transfer from protein to protein down the line.
What are some examples of possible cellular responses to signal transduction pathways?
The output of signal transduction pathways may include
- Changes in enzyme activity
- Opening/closing of ion channels
- Changes in gene expression (inc/dec of protein prod.)
How do cells integrate multiple signals (e.g. in making complex decisions)?
Different signal transduction pathways may regulate the same second messenger, enabling “cross-talk” between pathways.
What is cryptochrome an example of?
Cryptochrome is a receptor that responds to an abiotic stimulus - blue light. When (plant AND animal) cells perceive blue light this activates signal transduction cascades that regulate many processes inc. the body clock.
Can signal molecules move between different organisms?
Volatile molecules can move between plant/animal individuals. This chemical communication can co-ordinate behaviour, env.mentl response etc.
E.g. damaged plants release volatile signalling molecules to warn nearby plants to mount a defense to attack.
E.g. insect pheromones control mating, repro aggression.
Exergonic vs endergonic?
Exergonic: energy is released (products are lower energy than reactants)
Endergonic: energy is absorbed (products are higher energy than reactants)
Note: change in free energy not heat (which is endo/exothermic
What is the first law of thermodynamics?
1st law of thermodynamics: energy neither created nor destroyed
What is the 2nd law of thermodynamics?
2nd law of thermodynamics: the level of disorder tends to increase
What is an enzyme? How do they change reaction rates?
An enzyme is a protein that acts as a catalyst. They can speed the rate of the reaction by lowering the activation energy so its easier for reactions to occur when substrates bind to the enzyme. Substrates can enter and leave the active site and so the enzyme is re-used after products are ejected.
What is a substrate?
The substrate is the reactant affected by an enzyme. The enzyme binds to the substrate to form an enzyme-substrate complex.
What is the active site?
The active site is the region of the enzyme where the substrate binds
- Usually shaped especially to fit the substrate.
- Binding with a substrate can change the shape (conformation) of the enzyme.
What are the ways that an enzyme can lower the Ea barrier?
When a substrate binds to an active site the Ea barrier can be changed by…
- Orienting substrates correctly
- Straining substrate bonds (changes shape)
- Providing a favourable microenvironment
- Covalently bonding to the substrate
What are the factors influencing enzyme activity?
Enzymatic activity is affected by..
- Temp
- pH
- Co-factors
- Inhibitors
How does temperature affect enzymatic activity?
Increasing temperature…
- Influences protein shape + bond strength
- can speed the rate of the reaction but if increases too much proteins denature - become inactivated.
What are enzyme co-factors?
Enzyme co-factors are non-protein enzyme helpers that assist some enzymes in catalysis. E.g. help recognise, attract/repulse a substrate or product
Can be organic or inorganic
What are the key types of enzyme inhibitors?
Competitive inhibitors: bind to the active site and block out the subtrate
Noncompetitive/allosteric inhibitors: bind to another part of the enzyme, causing it to change shape so the active site is less effective.
Can be reversible or irreversible (which makes enzyme permantly inactivated).