LS 7C: Midterm 1 Learning Objectives
Test Questions and All Correct
Answers 2026Updated.
Discuss how a signal can lead to both short- and long-term responses - Answer Signaling cell
—> signaling molecule —> receptor protein —> responding
Signal binds and receptor is activated
(conformational change)
Signal transduction— one molecule activates
the next
Response— enzyme activation, turn on genes,
signal other cells, cause transcription of
proteins
Receptor Kinase activity because changes gene expression=> long-term
G-Protein-coupled receptor and ion channel receptors=> short term
Long
Transported by the circulatory system
example: Endocrine Signaling: Adrenaline,
estrogen and testosterone
Short
Moves by diffusion
Example: Paracrine— two cells close to one
another: Small, water-soluble molecule (i.e.
growth factor)
Autocrine signaling-Signaling molecule
released by a cell and binds to receptors on the
same cell: When an embryo specializes cell
types, this can reinforce this decision
Cell-to-cell contact: signaling molecule is not
actually released from the cell, transmembrane
protein
,When the two cells are far apart, the signaling molecule is transported by the circulatory
system. When they are close, the signaling molecule simply moves by diffusion. Many cells in
multicellular organisms are physically attached to one another; in this case, the signaling
molecule is not released from the signaling cell at all.
Short Term Response:
● Paracrine signaling: Signaling molecules travel a short distance to the nearest neighboring cell
to bind its receptor and deliver its message.
■ In paracrine signaling, the signal is usually a small, water-soluble molecule such as a growth
factor. A growth factor is a group of small, soluble molecules that affect cell growth, cell division,
and cause changes in gene expression. Growth factors help shape
the structure of an adult's tissues, organs, and limbs.
● Autocrine signaling: Signaling between different parts o
Describe the mechanism of action for a receptor tyrosine kinase pathway - Answer
Responses from receptor kinases tend to involve changes in gene expression, which allow cells
to grow, divide, differentiate, or change shape LONG TERM CHANGES
Each kinase activates the next and so one signal can cause a prolonged response
A tyrosine kinase pathway:
■ Receptor kinases bind signaling molecules, dimerize, phosphorylate each other, and activate
intracellular signal
molecules.
1. Inactive receptor:
a. The signal molecules bind to the
extracellular portion of the receptor.
2. Dimerization:
a. Causes a conformational change in the
cytoplasmic domain which activates the
tyrosine kinase catalytic activity.
b. ATP is converted to ADP in this process.
3. Active receptor:
a. The conversion of ATP to ADP allows each
member of the receptor pair to attach
phosphate groups to one another; in other
, words, phosphorylation occurs.
4. These phosphate groups provide binding sites for intracellular signaling proteins, which
activate them.
Define the role of kinases and phosphatases in cell signaling pathways - Answer Kinases—
enzyme that catalyzes the transfer of a phosphate group from ATP to a substrate
(phosphorylation), which activates the protein
Phosphotases— remove a phosphate group (dephosphorylation), and protein becomes inactive
○ Kinase:
■ an enzyme that catalyzes the transfer of a phosphate group from ATP to a substrate. To
catalyze this reaction, it
binds both ATP and the substrate. This process is called phosphorylation.
● When a protein is phosphorylated by a kinase, it becomes active and is switched on. The
addition of a phosphate group to a protein can activate it by
altering its shape or providing a new site for other proteins to bind.
○ Phosphatase:
■ removes a phosphate group, a process called dephosphorylation.
● When a protein is dephosphorylated by a phosphatase, it typically becomes inactive and is
switched off.
Distinguish the potential for differentiation of totipotent, pluripotent, and multipotent stem
cells - Answer Totipotent— can give rise to a complete organism (most potential)
Pluripotent— can become any of the three germ layers (ectoderm, mesoderm, endoderm).
(Less potential)
Multipotent— can form a limited number of specialized cells (least potential)
Evaluate why diffusion and surface area limit cell size and its implications for large, multicellular
organisms - Answer cells can't get too big or else the volume to surface area is decreased and
there is less surface area to absorb/diffuse. Waste removal faster in small cell. Implications: lots
of little cells for large, multicellular organism.
As volume increases, surface area decreases
Test Questions and All Correct
Answers 2026Updated.
Discuss how a signal can lead to both short- and long-term responses - Answer Signaling cell
—> signaling molecule —> receptor protein —> responding
Signal binds and receptor is activated
(conformational change)
Signal transduction— one molecule activates
the next
Response— enzyme activation, turn on genes,
signal other cells, cause transcription of
proteins
Receptor Kinase activity because changes gene expression=> long-term
G-Protein-coupled receptor and ion channel receptors=> short term
Long
Transported by the circulatory system
example: Endocrine Signaling: Adrenaline,
estrogen and testosterone
Short
Moves by diffusion
Example: Paracrine— two cells close to one
another: Small, water-soluble molecule (i.e.
growth factor)
Autocrine signaling-Signaling molecule
released by a cell and binds to receptors on the
same cell: When an embryo specializes cell
types, this can reinforce this decision
Cell-to-cell contact: signaling molecule is not
actually released from the cell, transmembrane
protein
,When the two cells are far apart, the signaling molecule is transported by the circulatory
system. When they are close, the signaling molecule simply moves by diffusion. Many cells in
multicellular organisms are physically attached to one another; in this case, the signaling
molecule is not released from the signaling cell at all.
Short Term Response:
● Paracrine signaling: Signaling molecules travel a short distance to the nearest neighboring cell
to bind its receptor and deliver its message.
■ In paracrine signaling, the signal is usually a small, water-soluble molecule such as a growth
factor. A growth factor is a group of small, soluble molecules that affect cell growth, cell division,
and cause changes in gene expression. Growth factors help shape
the structure of an adult's tissues, organs, and limbs.
● Autocrine signaling: Signaling between different parts o
Describe the mechanism of action for a receptor tyrosine kinase pathway - Answer
Responses from receptor kinases tend to involve changes in gene expression, which allow cells
to grow, divide, differentiate, or change shape LONG TERM CHANGES
Each kinase activates the next and so one signal can cause a prolonged response
A tyrosine kinase pathway:
■ Receptor kinases bind signaling molecules, dimerize, phosphorylate each other, and activate
intracellular signal
molecules.
1. Inactive receptor:
a. The signal molecules bind to the
extracellular portion of the receptor.
2. Dimerization:
a. Causes a conformational change in the
cytoplasmic domain which activates the
tyrosine kinase catalytic activity.
b. ATP is converted to ADP in this process.
3. Active receptor:
a. The conversion of ATP to ADP allows each
member of the receptor pair to attach
phosphate groups to one another; in other
, words, phosphorylation occurs.
4. These phosphate groups provide binding sites for intracellular signaling proteins, which
activate them.
Define the role of kinases and phosphatases in cell signaling pathways - Answer Kinases—
enzyme that catalyzes the transfer of a phosphate group from ATP to a substrate
(phosphorylation), which activates the protein
Phosphotases— remove a phosphate group (dephosphorylation), and protein becomes inactive
○ Kinase:
■ an enzyme that catalyzes the transfer of a phosphate group from ATP to a substrate. To
catalyze this reaction, it
binds both ATP and the substrate. This process is called phosphorylation.
● When a protein is phosphorylated by a kinase, it becomes active and is switched on. The
addition of a phosphate group to a protein can activate it by
altering its shape or providing a new site for other proteins to bind.
○ Phosphatase:
■ removes a phosphate group, a process called dephosphorylation.
● When a protein is dephosphorylated by a phosphatase, it typically becomes inactive and is
switched off.
Distinguish the potential for differentiation of totipotent, pluripotent, and multipotent stem
cells - Answer Totipotent— can give rise to a complete organism (most potential)
Pluripotent— can become any of the three germ layers (ectoderm, mesoderm, endoderm).
(Less potential)
Multipotent— can form a limited number of specialized cells (least potential)
Evaluate why diffusion and surface area limit cell size and its implications for large, multicellular
organisms - Answer cells can't get too big or else the volume to surface area is decreased and
there is less surface area to absorb/diffuse. Waste removal faster in small cell. Implications: lots
of little cells for large, multicellular organism.
As volume increases, surface area decreases
