BIO 131 exam 2 materials

What cellular structure is usually involved in cellular communication?

cell membrane

What kind of cells communicate via direct contact?

eukaryotic cells

What are the three stages of cell signaling?

1. reception

2. transduction

3. response

Signal Transduction Pathways: What happens inside of a cell when a signal has been received? Why?

When cells release signal molecules + the message is received there are various types of responses, EX: gene turned on, protein is manufactured, enzyme is activated

Steps of signal transduction

1. Ligand bonds to a receptor protein

2. Relay proteins are activated down a chain

3. The signals amplify until response is reached

Following activation of a receptor, which sequence below represents the correct order in which components will be involved in a signaling pathway that utilizes the second messenger cAMP?

G protein → adenyl cyclase → cAMP → protein kinase

Why do some signals (first messengers) trigger “second messengers” to activate target cells?

The first messenger cannot cross the plasma membrane

Which of the following is a substance that acts at a long distance from the site at which it is secreted?

hormone

To what does the term "ligand" refer in cell biology?

any small molecule that can bind in a specific manner to a larger one

Why can a signaling molecule cause different responses in different cells?

The transduction process is unique to each cell type; to respond to a signal, different cells require only a similar membrane receptor.

Lipid-soluble signaling molecules, such as aldosterone, cross the membranes of all cells but affect ONLY target cells because ________

intracellular receptors are present only in target cells

Phosphorylation cascades involving a series of protein kinases are useful for cellular signal transduction because ______

they amplify the original signal manyfold.

Why are there often so many steps between the original signal event and the cell's response?

Each step in a cascade produces a large number of activated products, causing signal amplification as the cascade progresses.

Which of the following are among the most common second messengers?

calcium ion and cAMP

Which of the following provides molecular evidence that signal transduction pathways evolved early in the history of life?

The molecular details of cell signaling are quite similar in organisms whose last common ancestor was a billion years ago.

As a form of local signaling, cells may communicate by direct contact of cells that are close to each other

In signal transduction, what enzyme transfers phosphates from ATP to a protein? (think abt what this process is called)

protein kinases

What is the purpose/change often enacted when phosphate groups are added to a protein (phosphorylation)?

changes protein from inactive → active (which can then enact a cellular response)

The process of protein kinases transferring phosphate from ATP and adding them to a protein?

phosphorylation

The process of protein phosphatases removing phosphate from proteins?

dephosphorylation

In signal transduction, what enzyme removes phosphates from a protein? (think abt what this process is called)

protein phosphatases

What is the purpose/change often enacted when phosphate groups are removed from a protein (dephosphorylation)?

turning off pathway, makes protein kinases available for reuse

Many relay molecules in a signal transduction pathway acting as kinases that act upon other kinases?

phosphorylation cascade

Protein kinases are activated by removing a phosphate from ___, which ends up turning that into ___

ATP

ADP

Once enough protein kinases are activated, often through a phosphorylation cascade, what occurs?

cellular response

The ligand that binds to the receptor in a pathway is known as?

the first messenger

Second messengers are: (3 properties), molecules or ions that spread throughout the cell via _____.

• small

• nonprotein

• water-soluble

diffusion

Name two common second messengers:

• cAMP

• Ca+/Na+

First messengers (do/don’t) enter the cell

don’t

Second messengers are great at ____ _______ between the signal molecule and many target molecules

signal amplification

When functioning as a second messenger, cAMP has the first effect of activating what?

protein kinase A

The _____ ______ can occur in the cytoplasm or the nucleus

cellular response

When a signaling pathway enters the nucleus, they often result in a final activated molecule known as a _____ _____, which regulates what?

transcription factor

gene expression

Steps of a nuclear response in cell signaling

1. receptor is activated at membrane

2. G protein activates adenylyl cyclase

3. cAMP is created and activates protein kinases down phosphorylation cascade

4. final molecule: transcription factor enters nucleus

5. transcription factor causes gene expression

Cell signaling occurring in the cytoplasm regulated the activating of

existing enzymes

Cellular responses occurring in the cytoplasm, give two examples!

• opening ion channel

• change in cell metabolism

What kind of cells may communicate via direct contact? how?

eukaryotic, cell junctions directly connect cytoplasms

animals: gap junctions

plants: plasmodesmata

Type of local signaling where small molecules travel short distances

paracrine signaling

Growth factors stimulate cells to grow + divide through _____ signaling

paracrine

Neurotransmitters/synaptic signaling is a specialized example of _____ signaling

paracrine

Long distance signaling in plants and animals is facilitated by using chemicals called:

hormones

Endocrine signaling causes hormones to travel through?

circulatory system

detection of the signal

reception

conversion of the signal to a cellular response via signal transduction pathway

transduction

cellular activity in response to the signal

response

Most signal receptors are:

plasma membrane proteins

Binding of ligans + receptor are highly:

specific

Ligand binding generally casuse a ____ ____ in the receptor, which typically directly activated many other receptors

shape change

(conformational change)

Three main types of membrane receptors:

1. GPCR

2. ligand-gated ion channels

3. receptor enyzme

Earl W. Sutherland discovered cell signaling by investigating hormone _______

epinephrine

(T/F) Reception can occur inside + outside the cell

true!

Most ligands that bind to plasma membrane proteins are ____ soluble

water

Once GPCR is activated, the shape changes + binds with a G protein, using ____ to become activated

GTP

Examples of signaling molecules that use GPCR’s

epinephrine

hormones

neurotransmitters

Type of receptor that allows/blocks the diffusion of specific ions across the membrane

ligand-gated ion channel

What system of the body are ligand-gated ion channels highly important?

nervous system (its the fastest method of cell signaling!! makes sense to use it in nervous system)

Two examples of specific ions that are controlled by ligand-gated ion channels?

Na+ and Ca+

What kind of messengers would use intracellular receptors?

• small

• hydrophobic

Steroid + thyroid hormones are examples of messengers that would utilize ____ receptors

intracellular

More opportunities for coordination + regulation of cellular response are done with?

cascades/ multi-step pathways

The molecules that relay a signal from receptor to response are often:

proteins

Each step of signal transduction causes what?

change in form (often physical shape)

The process of ATP + H20 in a hydrolysis reaction results in?

ADP

which releases energy!

Is hydrolysis from ATP → ADP exergonic/endergonic?

exergonic

Reactions that require energy input?

endergonic

Reactions that release free energy

exergonic

The sum of all chemical reactions occurring in an organism at a given time?

Metabolism

Energy changes in living systems occur as chemical changes (released/stored in chemical bonds)

Metabolism

Building up complex molecules, ______ energy, is what kind of reaction?

consumes

Anabolic

Breaking down complex molecules, ______ energy, is what kind of reaction?

creates/releases

Catabolic

Process of using exergonic reactions to drive endergonic reactions

energy coupling

Metabolism is a system broken into two modes of function:

anabolism

catabolism

Chemical agent that speeds up a reaction without being consumed by the reaction:

catalyst

A macromolecule that acts as a catalyst:

enzyme

Most enzymes are:

proteins

The energy required to start a reaction by breaking bonds in the reactant molecules

activation energy

Activation is often supplied by_____ that reactant molecules absorb from surroundings.

heat (or enzymes!!)

What is the transition state of a reaction?

the position in which bonds of reactant molecules are unstable enough to break

Heat is a _______ catalyst, making it precarious as it can ______ proteins

nonselective

denature

enzymes catalyze reactions by lowering the________ barrier, without being ______.

activation energy

consumed!

Enzymes (do/don’t) change the free energy

do not!

When conducting exergonic reactions, does energy need to be inputted to enact activation?

yes!

T/F: The same about of free energy is created with + without an enzyme

true

The _____ is the reactant molecule on which an enzyme acts

substrate

The enzyme binds to its substrate forming an:

enzyme-substrate complex

Most enzyme names end in:

-ase

Steps of active site/catalytic cycle of an enzyme: (6 steps)

1. substrates bind with enzyme

2. enzyme changes shape into induced fit + held by weak bonds (hydrogen)

3. active site lower activation energy + speeds up reaction

4. substrates are converted into products by enzyme

5. products are released

6. active site returns to original configuration

How do active sites lower activation energy + speed up reactions? (4 ways)

• orienting substrates correctly

• providing favorable microenvironmental conditions

• straining substrate bonds

• forming temp covalent bonds

What environmental factors can affect enzyme activity?

temp
pH

When outside of their temp or pH range, what happens to enzymes?

they become denatured + lose function

Nonprotein molecules that help carry out processes that are difficult for amino acids:

cofactors

What is an organic cofactor referred to as?

coenzyme

Most vitamins act as _____

coenzymes

Competitive inhibitors inhibit enzyme function by:

binding to active site of an enzyme to prevent the substrate from binding to it

Non-Competitive inhibitors inhibit enzyme function by:

binding to alternative site on enzyme + causes active site to change shape and become less effectively

Most enzymes are proteins encoded by:

genes

Cells tightly regulate metabolic pathways in 2 ways:

• switching on/off genes that encode for enzymes

• regulating the activity of already formed enzymes