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20 Cards in this Set

  • Front
  • Back
Cell-Cell communication
Essential for multicellular and single-celled organisms

Usually via chemical messengers called Ligands

Ligands are called alpha factors
What is local signalling?
A signal that travels short distances (only a few cells)

Cells may communicate via direct contact

Animal and plant cells have cell junctions that directly connect the cytoplasm of adjacent cells

cells communicate using local regulators
What is long distance signalling?
signals travel long distances through many cells, throughout the body.
What is Paracrine Signaling?
A signaling cell releases messenger molecules into the extracellular fluid. These local regulators influence nearby cells.
What is synaptic signaling?
a nerve cell releases neurotransmitter molecules into the narrow synapse separating it from its targe cell.
What are Hormones?
Chemical signals that travel to more distant cells. In hormonal or endocrine signalling the circulatory system transports hormones throughout the body to reach target cells with appropriate receptors. Transmission of signals through the nervous system is also a type of long-distance signaling.
What are the 3 stages of cell signaling?
1. Receiving (reception)

2. Transduction (the signal has been transformed)

3. Response
A signal molecule binds to a receptor protein causing it to change shape

The protein and the signal molecule both change shape

The receptor must change shape

Binding between signal molecule (ligand) and receptor is highly specific

Receptors may be either inside the cell (intracellular) or on the external plasma membrane
Intracellular receptors
are cytoplasmic or nuclear proteins

steroid hormones bind to intracellular receptors
Receptors in the External Plasma Membrane
There are 3 main types of membrane receptors

1. G-protein linked receptors (proteins)

2. Receptor Tyrosine Kinases (enzymes)

3. Ligand-Gated Ion Channel Receptors(gate)
Signal Transduction
Cascades of molecular interactions relay signals from receptors to target molecules

At each step in a pathway, the signal is tranduced into a different form, commonly a conformational change in a protein
What are multistep pathways?
Can amplify a signal

Provide more opportunities for coordination and regulation
What are Protein Phosphorylation Cascades?
Requires energy (use of ATP)

Is an example of signal transduction pathway

In this process

A series of protein kinases add a phophate to the enxt one in line, activating it

Phosphatase enzymes then remove the phosphates
What are Scaffolding Proteins?
Scaffolding proteins link relay proteins together like a scaffold so that they stay together.

Increase the signal transduction energy

External signal molecule maybe local or long distance. Is the first messenger then messages goes between relay proteins called secondary messengers.
Secondary Messengers
Carry message inside cell ("first messenger" carries messages between cells)

Are small, non-protein, water-soluable molecules or ions


cAMP (cyclic adenosine monophosphate)


IP3 (inositol triphosphate)

DAG (diacylgycerol
What is Cyclic AMP (cAMP)
ATP is made into cAMP by the enzyme adenylyl cyclase

Made up of 3 ATP, 2 ADP and 1 Phosphate

Acts as a second messenger in cellular pathways

eg of second messenger - Calcium (cation 2)

May be received by calmodulin receptor

Often activates protein kinase A which phosphorylates other proteins.
What happens in Cytoplasmic and Nuclear Responses?
Signaling pathways regulate a variety of cell activities

Metabolism, including enzyme functino might change

Changes in the membrane permeability

Cytoskeleton changes

Cell growth and reproduction

EG's Hormone Epinephorine and glucose release
What do Nuclear responses do?
regulate genes by turning genes on or off
What is Specificity of Cell Signaling
The different combinations of proteins in a cell

Give the cell great specificity in both the signal it detects and the responses it carries out
What are scaffolding proteins?
Large relay proteins to which other relay proteins attach, increasing the efficiency of signal transduction in a pathway.