bi108 quiz 5 unit 1

homeostasis

biological systems maintain stability while adjusting the changing external conditions 

control systems; and what is the controlled variable?

sense when conditions deviate from ‘normal’and initiate physiological mechanisms to correct the error. These systems work to restore balance in the body. Temperature is controlled

set point

reference point

feedback information

information that is compared to the set point by the sensor 

error signal

any difference between set point and feedback information 

effector

• tissues or organisms that can alter the internal environment 

negative feedback

• information that that returns system to set point (returns system to homeostasis)

positive feedback

• amplifies a response and increases deviation from a set point (pushes system away from homeostasis)

What is the purpose of negative feedback in blood glucose regulation?

To keep blood glucose levels constant — even when food intake varies throughout the day.Why does every cell need glucose?

Why does every cell need glucose?

Each cell must produce its own ATP, which requires glucose for cellular functions.

Which organ produces insulin and glucagon?

The pancreas — it contains multiple cell types that each secrete different hormones.hat dw

what does the liver do with excess glucose?

It stores excess glucose as glycogen for later use.

What are the two key hormones in glucose regulation and where are they made?

insulin and glucagon — both produced by different cell types in the pancreas.

How does the body respond when blood glucose rises after a meal?

The pancreas releases insulin, signaling the liver to convert glucose into glycogen (storage), lowering blood glucose back to normal.

how does the body respond when glucose levels drop between meals?

The pancreas releases glucagon, signaling the liver to break down glycogen back into glucose, raising blood glucose back to normal.

why do we need cell signaling

it allows cells to communicate, coordinating activities like growth, differentiation, and metabolism, ensuring the organism functions as a unified whole

classic example of positive feedback in the body

childbirth — the baby's head stretches the cervix, triggering uterine contractions, which push the baby down further, causing even more stretching and stronger contractions.

what triggers uterine contractions during childbirth

Stretching of the cervix by the baby's head — this sends a signal that stimulates contractions.

why is childbirth a positive and not a negative feedback?

Because the response (contractions) amplifies the original stimulus (cervical stretch) rather than counteracting it — the cycle keeps intensifying until birth.

what two environments does a cell monitor during signaling

extracellular and intracellular

steps of signaling pathways

reception, transduction, cellular response eceptior

reception (signaling pathways)

iratnformation is transmitted by a signal and received by a receptor 

transduction (signaling pathways)

Conversion of signal to a cellular response 

cellular response

Changes in cell behavior in response to the signal 

juxtacrine

cell signaling requiring physical contact utos

autocrine

self-effect; signal affects cell that produced the signal

paracrine

signal only affects nearby cells nr

endocrine

signal travels to distant cells - hormones

intracellular receptors

receptors are within the cell and bind to a signalling molecule that can pass through the lipid bilayer 

membrane receptors

 embedded in cell membrane; bind to signaling molecules outside of the cell 

what is a ligand?

A signaling molecule that binds to a receptor to trigger a response in the cell.

Where can receptors be located in a cell?

intracellular (inside the cell) or embedded in the cell membrane

Are receptors specific or general — can any ligand bind to any receptor?

highly specific; each receptor can only bind its specific ligand

What are the two sources a signaling ligand can come from?

The external environment (chemical or physical stimuli from outside the organism) or from neighboring cells.

What happens when a ligand binds to its receptor?

it triggers a conformational change — a shift in the receptor's shape.

What does the conformational change in a receptor do

It initiates a chain of subsequent events inside the cell, passing the signal forward.

What is the overall sequence of receptor-ligand signaling?

Ligand binds receptor → conformational change occurs → downstream events are triggered inside the cell.

what is a signaling transduction

The conversion of an external signal into a cellular response.

What is a signaling cascade?

A chain reaction where the signal is passed through multiple signaling proteins in sequence, each activating the next.

signal amplification

When a small amount of signal molecule triggers a much larger cellular response — the signal grows as it moves through the cascade.

How does amplification work at each step of a cascade?

One activated molecule can activate multiple molecules at the next step, multiplying the signal each time.

phosphorylation cascade

A common type of signaling cascade where proteins are activated by having a phosphate group added to them, passing activation forward step by step.

secondary messenger

A molecule released by the primary signal (ligand) that further amplifies the signal inside the cell.

What is the relationship between signal transduction and signal amplification?

Transduction converts the signal into a response; amplification ensures that even a tiny initial signal can produce a large, effective cellular response.

cellular response

• A cell changes behavior in response to the signal 

Can the result of a signaling pathway be short term or long term?

Both — signaling pathways can produce quick, temporary changes or lasting, long-term effects depending on the pathway and context.

What are three possible outcomes of a signaling pathway?

Changes in gene expression, a change in the rate of cellular respiration, or cell growth and division.

How can a signaling pathway produce long-term change?

By altering gene expression — turning certain genes on or off leads to lasting changes in what proteins the cell produces.

Why doesn't cell signaling last forever?

Signaling molecules don't stay bound to receptors indefinitely — they detach, get degraded, or are removed from the area.

What do phosphatases do, and why do they matter for turning off a signal?

Phosphatases remove phosphate groups from molecules in the pathway, inactivating them and halting the cascade.

How are the products of a signaling pathway eventually turned off?

Protein products (such as those made from gene expression) can be broken down, ending their effect.

What are the four main ways a signaling pathway is turned off?

Ligand unbinds the receptor, signaling molecules are degraded or removed, phosphatases inactivate pathway proteins, and protein products are broken down.

Why is cortisol unusual compared to most signaling molecules?

It's a steroid hormone, so it can cross the membrane and bind an intracellular receptor — most signals bind receptors on the cell surface.

Once cortisol activates its receptor, how does it actually change the cell?

The activated receptor becomes a transcription factor, directly regulating which genes get expressed — affecting glucose use, blood pressure, immune function, and more.

why do CDKs need cyclins

CDKs are always present but inactive on their own; cyclins are their on-switch, only made at specific points in the cell cycle.

mitogen role

Mitogens are ligands that tell the cell to divide — they kick off the pathway that leads to cyclin production

What happens to the mitogen receptor right after the ligand binds?

Two receptor molecules join together (dimerize), then phosphorylate each other, which activates the receptor.

How does the mitogen signal get from the membrane to the nucleus?

Through an enzyme cascade — each activated protein activates the next, amplifying the signal at every step until it reaches the nucleus.

What is the final outcome of the mitogen pathway?

Transcription of cyclin D — which activates CDKs and pushes the cell forward through the cell cycle toward division.

Why does epinephrine target the liver specifically during a stress response?

Because the liver stores glucose as glycogen — epinephrine signals it to stop storing and start releasing glucose into the blood so muscles can use it.

What type of receptor does epinephrine bind, and why does that matter?

A G-protein coupled receptor (GPCR) — binding activates an associated G protein, which then kicks off an amplifying cascade inside the cell.

What is cAMP and why is it important in this pathway?

cAMP is a second messenger made from ATP by adenylyl cyclase — it amplifies the signal by activating protein kinase A, spreading the response through the cell.

Protein kinase A does two things in this pathway — what are they and why do both matter?

It inactivates glycogen synthase (stops glucose storage) and activates phosphorylase kinase (starts glycogen breakdown) — both push glucose out into the blood.

How does the epinephrine pathway demonstrate signal amplification?

One epinephrine molecule can trigger release of ~10,000 glucose molecules — each step of the phosphorylation cascade multiplies the number of activated molecules.

What is a phosphorylation cascade and what role does it play here?

A chain of phosphorylation events triggered by a receptor — in this pathway it carries and amplifies the epinephrine signal from the membrane all the way to glycogen breakdown.

Trace the big picture: how does epinephrine binding a liver cell result in glucose in the blood?

Epinephrine → GPCR → G protein → adenylyl cyclase → cAMP → protein kinase A → glycogen breakdown → glucose released into bloodstream.