slide 2

Question 1

Cell to Cell Communication
A critical component of
a cell’s environment is
the presence of other
cells

Answer 1

Cell to cell
communication is
important in both
unicellular and
multicellular organisms

Question 2

The yeast,
Saccharomyces
cerevisiae, has
two mating types,
a and a1

Answer 2

Cells of different
mating types
locate each other
via secreted
factors specific to
each type.

Question 3

Some soil-dwelling
bacteria and amoebas
aggregate when food
becomes scarce and
form coordinated
fruiting bodies to
disperse spores

Answer 3

Release of signaling molecules
into the environment initiates
and regulates aggregation

Question 4

Multicellular organisms
can have trillions of
cells of hundreds of
different types

Answer 4

To maintain a functional
organism these cells
need to remain
coordinated through
communication

Question 5

Cell communication is important in the study of

many diseases and detrimental conditions:

Answer 5

– Cancer
– Allergies
– Heart disease
– Diabetes
– Alzheimer’s

Question 6

A signal transduction pathway

Answer 6

is a series of
steps by which a received signal is converted
into a specific cellular response.

Question 7

The molecular details of signal transduction

pathways are

Answer 7

very similar among unicellular

and multicellular organisms.

Question 8

Cells in a multicellular organism

communicate by chemical messengers

Answer 8

Communication is by either:
Local signaling
Long-distance signaling

Question 9

Local Signaling

Answer 9

Both animal and plant cells have cell junctions that

directly connect the cytoplasm of adjacent cells

Question 10

Animal cells can sometimes communicate via

direct contact in cell-cell recognition

Answer 10

(e.g. immune

response and embryonic development)

Question 11

local regulators

Answer 11

In many other cases,
animal cells communicate
using local regulators,
messenger molecules that
travel only short distances

Question 12

paracrine

Answer 12

In paracrine signaling
cells release molecules
that act on nearby cells

Question 13

Signals are passed

between nerve cells via

Answer 13

neurotransmitter
released into the
synapse (gap) between
the cells

Question 14

Long-Distance

Signaling

Answer 14

Animals and plants use
chemicals called
hormones for longdistance
signaling

Question 15

Endocrine signaling

Answer 15

involves release of
hormones into the
circulatory system

Question 16

The plant hormone

ethylene

Answer 16

is released to

coordinate fruit ripening

Question 17

3 stages of Cell Signaling

Answer 17

1) reception
2) transduction
3) response

Question 18

1. Reception

Answer 18

In signal reception a signal
molecule binds to a receptor
protein causing a shape change
Binding between signal (ligand)
and receptor is highly specific.

Question 19

1. Reception

Receptors can be located

Answer 19

A. in the plasma membrane

B. intracellularly (within cells)

Question 20

Plasma Membrane Receptors

Answer 20

There are three main types of membrane receptors
– G-protein-coupled receptors
– Receptor tyrosine kinases
– Ion channel receptors

Question 21

G protein-coupled receptors (GPCRs)

Answer 21

are the
largest family of human cell-surface receptors.
G Protein Coupled Receptors
Up to 60% of all medicines
act by influencing G
protein pathways.

Question 22

G Protein Coupled Receptors

Pathway involves:

Answer 22

• G protein-coupled receptor
• G-protein
• Enzyme

Question 23

G Protein Coupled Receptors
Binding a signal molecule
causes the receptor to change
shape and bind the G-protein;
GTP displaces GDP

Answer 23

Activated G-protein diffuses
along membrane and
activates enzyme

Bound GTP is
hydrolyzed to GDP,
G-protein dissociates
from enzyme and
becomes available for
re-use

Question 24

Receptor tyrosine kinases (RTKs)

Answer 24

are
membrane receptors that attach phosphates
to tyrosines.
A receptor tyrosine kinase can trigger
multiple signal transduction pathways
simultaneously.
Abnormal functioning of RTKs is associated
with many types of cancers.

Question 25

Ion Channel Receptors

Answer 25

When a signal molecule binds to the receptor,
the gate allows specific ions through.
Change in ion concentration (e.g. Na+
, Ca2+)
can have effects throughout the cell.

Question 26

Intracellular

Receptors

Answer 26

Signal molecules that
are small and
hydrophobic can
readily cross the
plasma membrane
(e.g. steroids)
Intracellular receptors
are found in the
cytoplasm or nucleus

Question 27

2. Transduction

Answer 27

Cascades of molecular interactions (multi-step
pathways) relay signals from receptors to target
molecules in the cell

Question 28

2. Transduction

Multistep pathways have some advantages:

Answer 28

• They can amplify a signal
• They provide more opportunities for
  coordination and regulation

Question 29

Phosphorylation Cascade

Answer 29

Many signal transduction
pathways include
“phosphorylation cascades”
– A series of enzymes add a
phosphate to the next one
in line, activating it
– different enzymes then
remove the phosphates

Question 30

3. Cellular Response

Answer 30

Cell signaling leads to regulation of cytoplasmic

activities or transcription of mRNA

Question 31

3. Cellular Response

In the cytoplasm

Answer 31

– Signals can be amplified through a multi-step
pathway (e.g. phosphorylation cascades)
– Signaling pathways regulate a variety of cellular
activities – e.g. a change in cell metabolism or shape

Question 32

3. Cellular Response

In the nucleus

Answer 32

– Regulate genes by
activating “transcription
factors” that turn genes
on or off

Question 33

Termination of Signals

Answer 33

Inactivation mechanisms are

also essential to cell functioning

Question 34

Termination of Signals

Answer 34

Signal response must be
terminated quickly
– By the reversal of ligand binding
– Receptor reverts to inactive form

Question 35

Example of cell signaling

Answer 35

Apoptosis

Question 36

Apoptosis –

Answer 36

“programmed cell death”

Question 37

Apoptosis is crucial in embryonic development, also occurs

in infected, damaged, or old cells

Answer 37

It is triggered by signals that activate “suicide proteins”