Test 3 Flashcards
A group of similar cells working together
tissue
collagen fibers that are interwoven with proteoglycans, helps holds cells together to form a tissue
extracellular matrix
direct contact
intercellular junctions
What are the junctions between plant cells?
plasmodesmata
What is animal cell contact?
tight junctions, gap junctions, and desmosomes
Numerous channels that pass between adjaent plant cells’ cell walls connect their cytoplasm, and enable transport of materials from cell to cell, and thus throughout the plant
plasmodesmata
Watertight sea between two adjacent animal cells, proteins (claudins and occludins) tightly hold the cells against each other
tight junction
long-distance chemical signals to communicate
hormones
What are the four steps of chemical communication?
- the signaling molecule is released in response to a stimulus from cells where the signal is synthesized and stored
2.The messenger travels from source cells to target cells - The signal binds to a receptor protein in a target cell.
- When a signal binds to a receptor, the protein changes shape in a way that acts as a trigger.
What are the five simple words for chemical signaling?
release, transport, receptor binding, and response
any molecule that binds to a receptor.
ligand
What are the three chemical families of animals?
amines, peptides, steroids
messengers are derived from the amino acids tryptophan or tyrosine
amines
small proteins
peptides
lipids that have a characteristic group of four ring structures
steroids
What are the key things to remember about all this variation in the structure of chemical messengers
- If the signaling molecule is small enough and hydrophobic enough, meaning that it has few partial charges and no full charges, it is lipid-soluble and can cross the outer membrane to enter the interior of target cells.
- If the signaling molecule is larger and more hydrophilic, due to the presence of partial or full charges, it is not lipid-soluble and cannot cross the outer membrane of target cells.
Some amine hormones and all _____ hormones are lipid-soluble and bind to receptors inside the cell.
steroid
Some amine hormones and all ______ hormones are not lipid-soluble and bind to receptors on the outside of the cell.
peptide
With the estrogen+ receptor complex, specific _______ in the DNA-binding domain make close physical contact with specific ______ ______ in DNA
R-groups, nitrogenous bases
refers to events that convert one type of signal to another type of signal. In the case of peptide hormones and most amine hormones, the receptor converts an extracellular signal to an intracellular signal.
signal transduction
is an enzyme that catalyzes the addition of a phosphate group from ATP to another molecule.
kinase
What happens once the intracellular signal is phosphorylated by the insulin receptor’s kinase activity?
The intracellular signaling networks that are activated by chemical messengers can lead to an array of outcomes.
Phosphorylation acts as an on-off or activation-deactivation switch for many proteins in a signaling network like this.
Cells can integrate information from an array of different chemical messengers because their signaling networks interact. Researchers call this “crosstalk.”
What is the key point about amplification?
a signal-receptor complex binds to the regulatory sequences for a particular gene, it can promote the production of many mRNAs.
When an activated receptor triggers a series of phosphorylation events, life scientists say that a ________ _______ occurs.
phosphorylation cascade
What is this describing?
the first kinase that is activated might add phosphate groups to 10 or more proteins. Those 10 proteins, in turn, may each go on to phosphorylate 10 or more proteins in the next step in the sequence. In this way, the original signal is amplified many times over. In terms of the number of molecules involved, the intracellular response is many times greater than the extracellular signal.
phosphorylation cascade
the response to signal binding is the release of substances
second messengers
channels that connect adjacent cells that allow solutes to pass between them for communication
gap junctions
form a watertight seal between adjacent cells and are made of claudins and occludins
tight junctions
spot connections between adajcent cells that hold them together and contain intermediate filaments
desmosomes
What are the three categories of cell-surface receptors that are involved in most of the intracellular signaling in multicellular organisms?
1.) Ion-channel-coupled receptors
2.) G-protein-coupled receptors
3.) enzyme-coupled receptors
What are the main three components of a cell-surface receptor?
1.) external ligand-binding domain (extracellular domain)
2.) an intracellular domain inside the cell
3.) transmembrane domain (hydrophobic membrane-spanning region)
Are cell0surface receptors specific or general to individual cell types?
Specific
_____-______-_____ ______ bind a ligand and open a channel through the membrane that allows specific ions to pass through
Ion-channel-coupled receptors
When a ligand binds to the extracellular region of the channel, there is a ______ _______ in the protein’s structure that allows ions such as sodium, calcium, magnesium, or hydrogen to pass through
conformational change
the _____ itself is almost always a single polypeptide chain with seven transmembrane domains that cross the membrane as alpha helices.
GPCR
With the GPCR, ____ is required to activate the G-proteins and allows a response to be generated.
GTP
What are the three subunits of the G-protein complex?
alpha, beta, gamma
Even though G-proteins are activated and move away from the receptor, the ______ ____ keep them associated with the interior surface of the plasma membrane
lipid tails
How do G-proteins deactivate themselves?
The Gα subunit will slowly hydrolyze the GTP so that it is converted back into GDP
In the GPCR, the response lasts only as long as the _____ does.
GTP
With Enzyme-coupled receptors, when the ligand binds to the receptor, an enzyme known as a ____ is activated.
kinase
What are the categories of kinase?
tyrosine kinases, or serine/threonine kinases.
With Enzyme-coupled receptors, what are the three important points about RTKS?
- RTKs usually dimerize as they bind to the signal molecule.
- Once they dimerize and the ligand is bound, the enzymatic activity is turned on.
3.The added phosphate groups on the receptor most commonly form the basis for docking sites so that a bunch of other proteins can bind and be phosphorylated.
phosphorylation and dephosphorylation of proteins are ____________ modifications
posttranslational
Phosphate groups are added to amino acids by _______ using ATP as the source of both the activation energy and the phosphate group.
kinases
What are the three amino acid side chains that kinases will add phosphate groups to?
serines, threonines, and tyrosines
Phosphorylation of _______ and ______ residues often activates enzymes.
serine and threonine
Phosphorylation of ______ residues can either affect the activity of an enzyme or create a binding site that interacts with downstream components in the signaling cascade.
tyrosine
small molecules that propagate a signal after it has been initiated by the binding of the signaling molecule to the receptor.
second messengers
Which second messengers are always produced together?
DAG and IP3
_____ will diffuse laterally through the membrane and act as a docking site for a protein known as protein kinase C (PKC).
DAG
____ is now soluble, so it can diffuse through the cytosol and bind to and activate its downstream targets.
IP3
____ can bind to is a ligand-gated ion channel in the ER. (which releases Calcium into the cytosol
IP3
made from ATP and is a signaling molecule commonly used in GPCR signaling cascades.
cAMP
______ _____ is produced when a plasma membrane–bound enzyme, adenylyl cyclase, is activated by the Gα subunit of the activated G-protein
Cyclic AMP
What are RTKs?
receptor Tyrosine kinases
What is intrinsic phosphorylation?
The dimer and receptors become an active enzyme and kinase activiity
What are the steps of enzyme coupled receptor?
-ligand binding dimerization
and activates kinase
domain
-Cross-phosphorylation
of tyrosine residues
outside of the kinase
domain
-Signaling proteins
bind to docking
sites to further
relay signal
-RTK acts as a
scaffold for
kinases and other
intracellular
proteins
With enzyme coupled receptors, do ligands come in pairs?
YES
Proteins that are bound to GDP are always (active or inactive)
inactive
What helps promote GDP to be released?
Guanine Exchange Factors (GEFs)
What is the process of releasing GTP phosphate group?
Hydrolysis
What is the protein that hydrolysis the GTP faster?
GTPase activating proteins (GAPs)
On GPCR, where is the cytosolic loop?
transmembrane segments 5-6
In the GPCR, what two subunits act like a dimer?
G-beta and G-gamma
True or false can the GPCR activate multiple copies of the G-protein?
TRUE
When will the GPCR stop activating g-proteins?
When the ligand stops binding
What enzyme is activated by the gamma alpha and gtp?
adenylyl cyclase
Where does IP3 as a ligand bind?
It binds to the ER lumen, calcium channels
What is the difference between kinases and second messengers?
second messengers are small molecules
kinases are relay proteins
What are the variety of different ways that the cell can release the signal?
-receptor downregulation
-receptor sequestration
-receptor inactivation
-signaling protein inactivation
What is receptor downregulation?
receptor and signal are destroyed in the lysosome(permanent)
What is receptor sequestration?
receptor is recycled and signal is destroyed (reversible)
What is receptor inactivation?
receptor is inhibited and signal can no longer be relayed (reversible)
What is signaling protein inactivation?
downstream signaling molecule is inhibited (reversible)
How do single-celled eukaryotes reproduce?
by cloning themselves- making a copy of their DNA and then undergoing cell division
____ phase is when mitosis and cell division occur
M
____phase is when growth and DNA replication occur
inter
What are the steps involved in chromosome condensing
The double helix wraps around balls of 8 histone proteins, forming a structure called a nucleosome; and
Nucleosomes are often clustered into compact arrays called 30-nm fibers.
A process in eukaryotes that is responsible for distributing a copy of each chromosome to each daughter cell. It occurs after chromosomes have been replicated and prior to the physical division of the parent cell into two daughter cells.
mitosis
The portion of the cell cycle when mitosis and cell division occur.
M phase
The portion of the cell cycle when growth and DNA replication occur.
Interphase
The initial phase of mitosis, when replicated chromosomes condense and the nuclear envelope breaks down.
prophase
The middle phase of mitosis, when replicated chromosomes move to the middle of the cell.
metaphase
The late phases of mitosis, when sister chromatids separate and one of each type of chromosome ends up at either end of the parent cell, then nuclear envelopes re-form around each set of chromosomes.
Anaphase and telophase
Cells that directly give rise to sperm or eggs, or are sperm or eggs themselves. Germ cells undergo meiosis to produce haploid daughter cells.
Germ cells
Cells that form the body, and that only undergo mitosis.
somatic cells
Which stages are in interphase?
G0, G1, S, G2
An orderly, highly regulated, and precisely controlled sequence of events that occurs as cells grow and divide.
cell cycle
Intervals in the cell cycle when regulatory proteins check specific aspects of the cell for damage, especially DNA, and allow or prevent continued progress through the cycle.
cell cycle checkpoints
The phases of the cell cycle where the cell undergoes normal growth processes and prepares for cell division.
interphase
a type of protein that regulates the progression of the cell cycle by activating cyclin-dependent kinases (Cdks).
cyclin
A cyclin-dependent kinase (Cdk) is an enzyme that, when activated by binding to a cyclin, plays a crucial role in regulating the cell cycle. Cdks phosphorylate specific target proteins, which helps drive the cell through different phases of the cell cycle.
Cdk
What is terminal differentiation?
cells that reach maturity, but they do not need to go through mitosis anymore. (ex. muscle cells)
What controls the cell checkpoints?
“gatekeeper proteins”
What are gatekeeper proteins?
proteins that respond to cellular conditions and will only allow the cell to move forward into the next phase of the cell cycle if conditions are “right.”
What are the conditions that need to be met for the cell to pass the G1/S checkpoint?
Proper nutrients (carbon source, energy source, inorganic phosphate, nitrogen, vitamins, etc.) must be present at specific concentrations.
Sister chromatid separation (from the previous mitosis) must be complete.
There must be no detectable DNA damage.
The cell must have reached a critical threshold size.
Where are the chromosomes when they are trying to pass the G2/M checkpoint?
they are lined up at the metaphase plate
Is the control of DNA synthesis and mitosis positive or negative controlled?
positive control, things enhance not inhibit
What is a kinase?
an enzyme that specifically adds phosphate groups to other proteins
What acts has a regulatory unit for CDK?
M cyclin
When is CDK activated?
When M cyclin is binded
How does the cell control activity of CDKs?
by controlling the synthesis and destruction of cyclins
What type of cyclin class is this?
Unique cyclins that are thought to help the cell respond to external signals to leave G0 and initiate cell division. We won’t discuss these any further in this book.
G1 cyclins
What type of cyclin class is this?
Cyclins that activate at the start of S phase (by the G1/S cyclins) and directly induce replication of DNA. The concentration of these cyclins remains high right through to M phase.
S cyclins
What kinase is considered an inhibitory phosphate for CDK and limits the activity of CDK?
Wee1
What kinase is necessary for the CDK to become active?
CAK
What transcription regulator manages the checking for DNA damage?
p53
When does M-cyclin-CDK have a positive feedback loop?
cdc25 which leads to activation
When does M cyclin-CDK have a negative feedback loop?
APC which leads to deactivation
What is the first portion of the mitotic phase called?
karyokinesis
What phases are in karyokinesis?
prophase, prometaphase, metaphase, anaphase, and telophase
In what phase do each sister chromatid develop a protein structure called a kinetochore?
prometaphase
What signal stimulates cell division?
mitogens
What signal stimulates cell growth?
growth factors
What signals suppresses the form of programmed cell death (APOPTOSIS)
survival factors
What happens in the cell cycle if conditions are unfavorable or there is no signal to proliferate?
- cell enters resting state (G0)
- terminal differentiation
What are the conditions that must be met for the cell to pass the G2 checkpoint?
-DNA replication must be complete and accurate
-No DNA damage
-cell must have reached minimum size
What conditions must be met for the M checkpoint (metaphase-to-Anaphase transition)?
-Mitotic spindles are assembled at opposite poles of cell
-chromosomes are aligned at the metaphase plate and properly attached to each spindle pole
How does M-Cdk drive entry into Mitosis?
- induces the assembly of the mitotic spindle
- triggers chromsome condensation
- promotes breakdown of the nuclear envelope
- promotes rearrangement of the actin cytoskeleton
What phases of mitosis is M-Cdk involved in?
prophase, prometaphase, metaphase
In what phase is cyclin D?
G1
What is cyclin D’s CDK?
CDK 4/6
in what phase is cyclin E?
S phase
What is cyclin E’s CDK?
CDK2
In what phase is cyclin A active?
end of S phase and G2
What is cyclin A’s CDK?
CDK2
What is the key cyclin and CDK in the M phase?
Cyclin B and CDK1
cyclin ___ is produced if there is enough growth factor signaling in the environment
D
cyclin ___ is required for replication initiation in S phase
E
What signals cyclin E?
E2F
What prevents pRB from binding to E2F complex?
Cyclin D and CDK4/6, it phosphorylates the pRB and E2F complex which allows E2F to bind to the DNA
What does p53 activate and why is that important?
p53 activates p21, p21 inhibits cyclin and CDK which pauses the cell cycle
When does the replication bubble form and what allows the replication bubble to form?
It forms beginning of the S phase and it is allowed through the cyclin E and CDKs which phosphorylate the complex
What is the purpose of cyclin B and CDK1?
-Through lamin dissociation, the nuclear envelop breaks down
-it phosphorylates the condensins
