Bio Unit 3

Contact-dependent Signaling

type of cell-to-cell communication where a membrane bound ligand on one cell binds directly to a membrane receptor on an adjacent cell

-Gap Junctions allow direct cytoplasmic transfer between cells:

• protein channels that connect adjacent cells

• small molecules can pass directly from cell-to-cell

• good for fast, unregulated communication (ex: cardiac muscle to ensure synchronous heartbeat)

Local/Paracrine Signaling

a form of local cell-to-cell communication where a cell releases chemical messengers into the extracellular fluid to affect nearby target cells within the same tissue microenvironment

• local communication involves the DIFFUSION of chemical signals

Long-distance Signaling

allows cells or organs to communicate across an entire organism using specialized transport systems

• The Endocrine and Nervous system carry out long distance communication

• Endocrine: chemical (ex: hormones travel through blood)

• Nervous: electrical + chemical (ex: action potentials (electrical nerve impulses) and Neurotransmitters (signaling molecules))

Receptor

protein that recognizes a specific signaling molecule and sends some signal within cell to change behavior

Endocrine Signaling

Chemical

ex: hormones travel through blood

Nervous System

Electrical + Chemical

ex: Action potentials (electrical nerve impulses) and Neurotransmitters (signaling molecules)

Agonist

mimics signaling molecule

-activates receptor/pathway

ex: morphine is an endorphin receptor agonist that reduces pain sensation

Antagonist

blocks receptor

-inhibits receptor/pathway

ex: caffeine is an adenosine receptor antagonist that blocks signals related to tiredness

Signal Transduction

Internal Amplification

• Enzyme-mediated: phosphorylation cascade, one enzyme activates the next

• Small molecule-mediated: second messenger - signaling molecule that is created and has effects inside of cell

First Messenger

extracellular signal molecule

Second Messenger

• activated intracellular molecules

• Ions (CA2+), Nucleotides (cAMP), lipid-derived (IP3), gases (NO)

• often produced by enzymes activated by receptor

Kinase

Protein enzymes that change protein activity by adding and removing phosphate groups

Phosphatase

Protein enzymes that change protein activity by adding and removing phosphate groups

3 Mechanisms of Signal Termination

1. Destroy Signal: enzymes brown down signal

2. Remove signal: reuptake transporters bring signals back inside cells

3. Remove receptor: endocytosis of receptor prevents cell from responding to further signals

How is endocrine signaling different from paracrine signaling?

Endocrine signaling acts on distant target cells located far away in other parts of the body while paracrine signaling acts on nearby cells within the same local tissue microenvironment

What is an agonist and what is an antagonist?

An agonist is a substance that binds to a receptor, mimicking the signaling molecule, and activates the pathway

An antagonist blocks the receptor and inhibits the pathway

How are hydrophilic and hydrophobic signals received differently? Why does this difference exist?

Hydrophobic signals:

-membrane permeable (direct diffusion)

-cytoplasmic or nuclear receptors, often directly regulate DNA

Hydrophilic signals:

-membrane impermeable (can’t directly cross membrane)

-membrane receptors

-signal ‘transduced’ into cell

This exists because of the polarity of the hydrophobic and hydrophilic molecules and the permeability of the membrane

Why are enzymes common parts of signal transduction pathways? What are some examples of

enzymes that are parts of signal transduction pathways?

Because they provide signal amplification, speed, and reversible regulation. Kinase and Phosphatases.

What are the systems that turn off signaling between cells? What happens if they are blocked?

Mechanisms of Signal Termination. Uncontrolled cell division or tumor growth, checkpoints may be “off” and molecules may not be stopped if incorrect leading to cancer cells.

What is a pathogen? What is a virus? How do viruses reproduce?

• Pathogens are agents that cause disease

• Viruses are a type of pathogen, an infectious agent that can’t reproduce on its own

• Viruses reproduce by using a host cell’s enzymes and monomers to replicate their genome and make the proteins they need

What is an antibody? What are the two ways we discussed that antibodies help to defeat pathogens?

• Antibodies are proteins produced by B cells which recognize antigens

• Antibodies protect in two ways: 1. they surround pathogens, making it difficult for them to attach to surface or invade cells 2. they help endocytic cells recognize and consume pathogens

How do Cytotoxic T Cells find pathogens that are inside of cells?

What is the role of Helper T Cells in the immune response?

T helper cells release signaling molecules that further activate B cells and other T cells, these signaling molecules are responsible for symptoms of inflammation, including fever and fatigue

How does the adaptive immune response build a large and targeted response against a specific pathogen?

by recognizing organic molecules specific to that pathogen called antigens (usually proteins or sugars)

What is a memory cell and how are they created?

Memory cells are B and T cells that stick around after an initial infection and cause a faster, bigger response when the pathogen returns

What is a vaccine and how do they work?

Vaccines deliver antigens from pathogens, without the danger posed by the actual pathogen.

Hormones

Reuptake Transporters

SSRI

Pathogen

agents that cause disease

Virus

viruses use a host cell’s enzymes and monomers to replicate their genome and make the proteins they need

Virus life cycle: virus invasion → genome replication → protein production → virus assembly

Antigen

organic molecules specific to pathogens (usually sugars or proteins)

Antibodies

proteins produced by B cells which recognize antigens, they protect in two ways

1. antibodies surround pathogens, making it difficult for them to attach to surfaces or invade cells

2. Antibodies also help endocytic cells recognize and consume pathogens

B cells

B cells emerge from the bone marrow with different and somewhat random antibodies that recognize different potential antigens

Clonal expansion

building a large and targeted response

MHC protein

used to display internal antigens on surface, usually these will be the cell’s own proteins and the immune system will not react to it

Cytotoxic T cell

kill infected cells when they present antigens that bind to TCR (T cell Receptor)

T Helper cell

contact-dependent antigen presentation activates T helper cells, T helper cells release signaling molecules that further activate B cells and other T cells, these signaling molecules are responsible for symptoms of inflammation, including fever and fatigue

Memory cell

memory cells are B and T cells that stick around after an initial infection and cause a faster, bigger response when the pathogen returns

Vaccine

vaccines deliver antigens from pathogens, without the danger posed by the actual pathogen

the goal of a vaccine is to create immunological memory without the live pathogen

Mitosis

separation of sister chromatids and distribution to daughter cells

Parent cell

the original cell that divides

Daughter cells

new cells created from division

Genetic material

substance that contains the information for how to build an organism, and for what each cell should do = DNA

Gene

individual unit of genetic information, a piece of DNA that codes for something

Chromosome

one continuous DNA molecule (or two combined identical DNA molecules)

Chromatin

DNA molecule wrapped around protein (histones)

-structure: organizes/compacts DNA

-function: regulates DNA

Centromere

Site (specific DNA sequence) where proteins bind to help divide chromosomes during cell division

-creates a cinched “waist”

Genome

the entirety of an organism’s hereditary information

Sister Chromatids

joined identical copies of original chromosome, created by DNA replication

DNA Replication

whole genome is duplicated so each daughter cell gets complete genome

Mitotic spindle

microtubules which pull the sister chromatids apart during mitosis

-spindle extends from centrosomes

Centrosomes

Kinetochore Microtubules

Polar (nonkinetochore) microtubules

Stages of Mitosis

Cytokinesis

Interphase

Cyclin

Cyclin-dependent kinase

Oncogene

Tumor suppressors

Terminally differentiated

Stem cells

Potency

iPSC

Cancer

Tumor

Benign Tumor

Malignant Tumor