Cell Communication and Multicellularity

Question 1

What are receptors and why are they important for cells?
A: Receptors are proteins embedded in the plasma membrane or free within the cell’s cytoplasm that enable cells to respond to signals. They are important because cells are constantly bombarded by signals and require appropriate receptors to respond.

Question 2

How do receptors give subtle and complex control to cells?
A: A varied range of receptors allows cells to respond to a wide range of signals, giving them subtle and complex control over their responses.

Question 3

What is a ligand?
A: A ligand is a signaling molecule that is specific for a particular receptor.

Question 4

Slide 4-5

Question 5

put into q&a flashcards:
Cytoplasmic receptors
Estrogen
It diffuses across the plasma membrane.
It then enters the nucleus and binds to the estrogen receptor.
The receptor then undergoes a conformational change resulting in its dimerisation.
The receptor dimer binds to specific genes and activates their transcription so that specific proteins are produced

Question 6

What are cytoplasmic receptors?
A: Cytoplasmic receptors are a type of receptor protein found in the cytoplasm of cells.

Question 7

How does estrogen enter the cell?
A: Estrogen diffuses across the plasma membrane.

Question 8

Where does estrogen bind once inside the cell?
A: Estrogen binds to the estrogen receptor, (located in nucleus)

Question 9

What happens to the estrogen receptor after binding to estrogen?
A: The estrogen receptor undergoes a conformational change, resulting in its dimerisation.

Question 10

What is the role of the estrogen receptor dimer?
A: The estrogen receptor dimer binds to specific genes and activates their transcription so that specific proteins are produced.

Question 11

What are plasma-membrane-bound receptors?
A: Plasma-membrane-bound receptors are a type of receptor protein located on the outer surface of the plasma membrane of cells.

Question 12

Why can’t many signalling molecules cross the plasma membrane?
A: Many signalling molecules are big and hydrophilic, which prevents them from crossing the plasma membrane.

Question 13

What types of signals bind to external plasma membrane-bound cell surface receptors?
A: Neurotransmitters, peptide hormones, and growth factors are examples of signals that bind to external plasma membrane-bound cell surface receptors.

Question 14

What happens when a signal binds to a plasma-membrane-bound receptor?
A: Binding of the signal to a receptor triggers a second intracellular signal.

Question 15

What are the two main types of plasma membrane-bound receptors?
A: The two main types of plasma membrane-bound receptors are ligand-gated ion channels and enzyme-linked receptors.

Question 16

What is another type of plasma membrane-bound receptor?
A: G protein-coupled receptors are another type of plasma membrane-bound receptor.

Question 17

put into q&a flashcards:
Plasma-membrane-bound receptors
Ligand-gated ion channels
Example; receptors for neurotransmitters in the nervous system.
Ligand-gated ion channels also sometimes allow flow of Ca2+ ions which is important in signal transduction.
A signalling molecule binds to ion channel proteins and the ion channel proteins change shape
The ion channel opens so that ions pass through, down their concentration gradient

Question 18

put into q&a flashcards:
Plasma-membrane-bound receptors
Ligand-gated ion channels
An example of a receptor for the neurotransmitter acetylcholine in the plasma membrane of skeletal muscle cells.
It is a sodium (Na+) channel protein that binds its ligand acetylcholine.
Acetylcholine is a neurotransmitter and is released by neurons.
When 2 molecules of acetylcholine bind to the receptor, the channel opens for 1/1000 sec.
Na+ ions move across the membrane, down their concentration gradient and muscles contract.

Question 19

put into q&a flashcards:
Plasma-membrane-bound receptors
Enzyme-linked receptors
These receptors are either enzymes, or are linked to enzymes.
The enzymes are often protein kinases which function by transferring a high energy phosphate from ATP to a protein.
Phosphorylation either activates or deactivates the target protein.
These receptors are single pass transmembrane proteins.
The part that binds the signal lies on the outside of the cell membrane.
The part that is an enzyme or activates an enzyme lies on the inside of the cell membrane.

Question 20

What are plasma-membrane-bound receptors?
A: Plasma-membrane-bound receptors are proteins that are located on the surface of cells and are responsible for transmitting signals from outside the cell to the inside.

Question 21

What are enzyme-linked receptors?
A: Enzyme-linked receptors are a type of plasma-membrane-bound receptor that are either enzymes or are linked to enzymes.

Question 22

What type of enzymes are often linked to enzyme-linked receptors?
A: Enzyme-linked receptors often have protein kinases linked to them. These protein kinases transfer a high energy phosphate from ATP to a protein.

Question 23

What is the function of phosphorylation in signal transduction?
A: Phosphorylation either activates or deactivates the target protein, which can trigger a cellular response.

Question 24

What is the structure of enzyme-linked receptors?
A: Enzyme-linked receptors are single pass transmembrane proteins, with the part that binds the signal located on the outside of the cell membrane, and the part that is an enzyme or activates an enzyme located on the inside of the cell membrane.

Question 25

How do enzyme-linked receptors transmit signals across the cell membrane? A: When a signaling molecule binds to the part of the receptor on the outside of the cell membrane, it causes a change in the shape of the receptor. This change in shape activates the enzyme or the linked enzyme, which initiates a cellular response.

Question 26

put into q&a flashcards: Enzyme-linked receptors Example - the Insulin receptor Insulin is made by the pancreas and acts as a signal that cells should absorb glucose. The insulin receptor is made up of 2 subunits (⍺ and β). Insulin binds to the ⍺-subunit of the receptor on the outside of the cell. This causes receptor dimerisation and its protein kinase function is activated on the cytoplasmic side. The protein kinase phosphorylates cytoplasmic proteins and activates them so that glucose uptake is stimulated.

Question 27

What are the two types of response of enzyme-linked receptors?

Answer 27

fast and slow response

Question 28

What is the slow response of enzyme-linked receptors?

Answer 28

The slow response of enzyme-linked receptors involves: - many intracellular transduction steps - causes a change in gene expression - leading to protein synthesis, cell growth, and/or differentiation - response typically takes hours to occur

Question 29

What is the fast response of enzyme-linked receptors?

Answer 29

The fast response of enzyme-linked receptors is: - direct and rapid effect on cellular function - occurs within seconds to minutes - does not require new gene expression as the proteins required for the response already exist (in cell)

Question 30

What is an example of the fast response of enzyme-linked receptors?

Answer 30

The response to chemicals attached to the surface on which a cell is crawling

Question 31

What are G protein-coupled receptors (GPCRs)?

Answer 31

Receptors that are involved in transmitting signals from outside the cell to inside the cell.

Question 32

How many different G protein-coupled receptors are there and what is their structure?

Answer 32

There are at least 100 different G protein-coupled receptors - all with a similar structure that includes 7 transmembrane domains

Question 33

What types of signalling molecules can activate GPCRs?

Answer 33

Different GPCRs can be activated by an enormous range of signalling molecules, including: - peptide hormones - neurotransmitters fatty acids - amino acids

Question 34

How are signals transmitted through GPCRs?

Answer 34

- via elaborate relay cascades - involve the activation of intracellular signaling proteins (G proteins) that interact with the receptor - to transmit the signal to downstream targets within the cell

Question 35

How do G protein-coupled receptors (GPCRs) work?

Answer 35

GPCRs work by interacting with and activating G proteins to form a transient link between the signal on the cell surface and a signal pathway in the cytoplasm.

Question 36

How are G proteins activated?

Answer 36

G proteins are activated when they bind to GTP (guanosine triphosphate).

Question 37

Why is the signal transmitted through GPCRs of very short duration?

Answer 37

The signal transmitted through GPCRs is of very short duration because the GTP bound by a G protein is quickly broken down into GDP (guanosine diphosphate) and P (phosphate).

Question 38

What is necessary to keep the G proteins 'switched on'?

Answer 38

To stay 'switched on', there must be a constant stream of signal molecules associating with the GPCRs to activate the G proteins.

Question 39

How are signals relayed into the cell?

Answer 39

Some enzyme-linked receptors and most G protein-coupled receptors transmit the signal across the membrane and into the cell and activate second messengers to relay the signal across the cytoplasm.

Question 40

What are second messengers and what are some examples?

Answer 40

Second messengers are usually ions or small molecules that are activated by the receptor and propagate the signal further into the cell. Examples of second messengers include Ca2+ ions or cyclic adenosine monophosphate (cAMP).

Question 41

How do second messengers amplify the signal?

Answer 41

Second messengers amplify the signal by activating other intracellular signaling proteins and cascades, leading to multiple downstream effects from a single initial signal.

Question 42

How is the signal amplified in signal transduction? A: The signal is amplified as it is passed from messenger to messenger. Each messenger is activated by phosphorylation and passes the message on to several others. A cascade of protein kinases amplifies the signal, allowing a weak signal from outside the cell to elicit a strong response inside the cell.

Question 43

What are some examples of receptors that receive signals from the outside of the cell? A: Examples of receptors that receive signals from the outside of the cell include G protein-coupled receptors (GPCRs) and enzyme-linked receptors.

Question 44

What are second messengers? A: Second messengers are molecules that are activated by cell surface receptors and propagate the signal further into the cell.

Question 45

How do protein kinases amplify the signal in a signaling cascade? A: Protein kinases amplify the signal in a signaling cascade by adding phosphate groups to proteins, which changes their shape and activity, and allows them to activate other proteins in the cascade. This allows for a weak signal to elicit a strong response inside the cell.

Question 46

put into q&a flashcards: Apoptosis is responsible for a number of critical cell functions and operates by the type of signalling mechanism we have been discussing Roles of apoptosis: Tissue ‘sculpting’ during embryogenesis Maintaining cell number Destruction of old / worn out cells Avoiding cancer Normal immune function Apoptosis: the death receptor pathway 1. A ligand trimer binds to the death receptor 2. This binding results in exposure of the receptor’s death domain. 3. Death domain binds adaptor. 4. Adaptor binds procaspase. 5. Procaspase becomes activated to caspase. 6. Caspase is released; initiates more ‘executioner’ caspases – they degrade proteins and activate DNase resulting in death of the cell

Question 47

What are the roles of apoptosis? Answer: Apoptosis is responsible for a number of critical cell functions, including tissue ‘sculpting’ during embryogenesis, maintaining cell number, destruction of old / worn out cells, avoiding cancer, and normal immune function.

Question 48

What is the death receptor pathway of apoptosis? Answer: 1. A ligand trimer binds to the death receptor 2. This binding results in exposure of the receptor’s death domain. 3. Death domain binds adaptor. 4. Adaptor binds procaspase. 5. Procaspase becomes activated to caspase. 6. Caspase is released; initiates more ‘executioner’ caspases – they degrade proteins and activate DNase resulting in death of the cell.

Question 49

What is the extracellular matrix (ECM)?

Answer 49

The ECM is a network of material secreted from cells forming a complex meshwork outside of cells.

Question 50

What is the function of the extracellular matrix (ECM)?

Answer 50

The ECM provides structural support, mechanical strength, and biochemical signaling to cells.

Question 51

Where is the extracellular matrix (ECM) found?

Answer 51

The ECM is a major component of certain parts of plants and animals such as: - woody parts of plants (the cell wall) - bone - skin - cartilage

Question 52

What is the composition of the extracellular matrix (ECM)?

Answer 52

The ECM is primarily composed of proteins and polysaccharides

Question 53

What are proteins in the extracellular matrix (ECM)?

Answer 53

Proteins are one of the most abundant macromolecules of the ECM

Question 54

What do proteins in the extracellular matrix (ECM) form?

Answer 54

Proteins in the ECM form large fibers

Question 55

What is the role of proteins in the extracellular matrix (ECM)?

Answer 55

Proteins in the ECM have important roles in providing - tissue strength - structural support - organization

Question 56

What are some examples of proteins in the extracellular matrix (ECM)?

Answer 56

Examples of proteins in the ECM include - collagen - elastin - fibronectin - laminin

Question 57

What is the role of collagen in the extracellular matrix (ECM)?

Answer 57

Provides tensile strength e.g. bones, cartilage, skin

Question 58

What are polysaccharides in the extracellular matrix (ECM)?

Answer 58

Polysaccharides are the 2nd major component of the ECM after proteins.

Question 59

What is the most abundant polysaccharide in the ECM of vertebrates?

Answer 59

Glycosaminoglycans (GAGs) are the most abundant polysaccharides in the ECM of vertebrates.

Question 60

What are GAGs?

Answer 60

GAGs are long, unbranched polysaccharides with a repeating disaccharide unit.

Question 61

Can you give examples of GAGs?

Answer 61

Chondroitin sulfate, found in cartilage, and hyaluronic acid, found in skin, eyes, and joint fluid, are two examples of GAGs.

Question 62

What is the function of GAGs in the ECM?

Answer 62

GAGs and proteoglycans (protein/polysaccharide complexes) form a gel-like component in the ECM, which resists compression.

Question 63

What is chitin?

Answer 63

Chitin is a polysaccharide that is important in the ECM of invertebrates because it forms the exoskeleton of arthropods.

Question 64

What is the ECM of plants?

Answer 64

The ECM of plants is the cell wall, which is located outside the plasma membrane and provides protection.

Question 65

What is the cell wall composed of?

Answer 65

The cell wall is a complex structure composed of secreted proteins and polysaccharides.

Question 66

What is the function of the cell wall in plants?

Answer 66

The cell wall provides rigidity for mechanical support of the plant, acts in maintenance of cell shape, and determines the direction of cell growth.

Question 67

How does the strength of the plant cell wall compare to the ECM of animals?

Answer 67

The plant cell wall is usually stronger, thicker, and more rigid than the ECM of animals.

Question 68

What is the primary cell wall in plants? A: The primary cell wall is a flexible structure that develops between newly made cells, allowing for cell size increase. Its main macromolecule is cellulose

Question 69

What is the secondary cell wall in plants? A: The secondary cell wall is often deposited between the plasma membrane and the primary cell wall after the plant cell matures, depending on the cell type. It has layers of cellulose and other components, such as lignin, in a more variable structure than the primary cell wall.

Question 70

What is lignin? A: Lignin is a complex organic polymer that is an important component of the secondary cell wall in plants. It is responsible for the strength and rigidity of the cell wall and is commonly known as "wood."

Question 71

What are cell junctions?

Answer 71

Long lasting physical connections between adjacent cells

Question 72

Why are cell junctions essential?

Answer 72

Essential for tissue organisation and function

Question 73

What are the 3 types of cell junctions in animals?

Answer 73

- tight junctions - anchoring junctions - gap junctions

Question 74

What are the 2 types of cell junctions in plants?

Answer 74

- middle lamella - plasmodesmata

Question 75

What are tight junctions?

Answer 75

Junctions between adjacent cells in a layer that prevent the leakage of material between cells. (seal tissues)

Question 76

What are anchoring junctions?

Answer 76

Cell junctions that hold adjacent cells together or attach cells to the ECM - mechanically strong. (anchor cells to eachother & to ECM)

Question 77

What are gap junctions?

Answer 77

Collection of channels that allow the direct exchange of ions and small molecules between the cytosol of adjacent cells. (allows communication between cells)

Question 78

What are the types of anchoring junctions?

Answer 78

- adherin junctions - desmosomes - focal adhesions - hemidesmosomes (don't need to know difference between them)

Question 79

What is the function of tight junctions? Answer: The main function of tight junctions is to prevent small molecules from leaking between the cells, maintaining selective permeability of cell sheets. They also maintain the cells as a wall, partitioning molecules on one side or the other, restrict migration of proteins and lipids from one region of the plasma membrane to another, and help ensure directional movement of materials in the body.

Question 80

How do tight junctions maintain the selective permeability of cell sheets? Answer: Tight junctions prevent small molecules from leaking between the cells, which maintains the selective permeability of cell sheets.

Question 81

What is the role of tight junctions in partitioning molecules? Answer: Tight junctions maintain the cells as a wall, partitioning molecules on one side or the other.

Question 82

How do tight junctions restrict migration of proteins and lipids? Answer: Tight junctions restrict the migration of proteins and lipids from one region of the plasma membrane to another

Question 83

What is the significance of tight junctions in the body? Answer: Tight junctions help ensure the directional movement of materials in the body, which is essential for proper organ and tissue function.

Question 84

put into multiple q&a flashcards Tight junctions prevent protein migration in the plasma membrane In polarised cells such as epithelial cells, tight junctions encircling the cell segregate transport proteins to the correct face of the plasma membrane Different transport proteins carry Na+ into the cell in it’s apical domain above the tight junctions, and K+ out of the cell and into the extracellular fluid from it’s basolateral domain below the tight junctions Na+ transport is directional simply because the transport proteins cannot diffuse from one plasma membrane region to the other due to the presence of tight junctions. Symmetrical cells have no tight junctions and, thus, no polarity in their transport mechanism

Question 85

How do connexons form a channel in gap junctions?

Answer 85

Connexons from adjacent cells line up to form a channel, with the membranes held apart.

Question 86

What type of molecules can pass through gap junctions? Answer: Small molecules such as sugars, amino acids, ions, and signaling molecules can pass through gap junctions from the cytoplasm of one cell into the next. However, large molecules such as proteins cannot pass through.

Question 87

What is the structure of connexons in gap junctions? Answer: Connexons in gap junctions are composed of six subunits of the protein connexin in a circle and protrude above the cell surface.

Question 88

What is the significance of gap junctions in the body? Answer: Gap junctions allow for direct communication and coordination between cells, which is essential for various biological processes, such as embryonic development, cardiac and smooth muscle contraction, and neuronal signaling.

Question 89

Connections between plant cells In plants, adjacent cells are cemented together by the middle lamella The middle lamella lies outside the cell wall. It is rich in pectins which are negatively charged polysaccharides, and Ca2+ and Mg2+, and attracts water to make a gel.

Question 90

How are adjacent plant cells connected?

Answer 90

Adjacent plant cells are cemented together by the middle lamella.

Question 91

What is the middle lamella in plant cells?

Answer 91

The middle lamella is a layer that lies outside the cell wall in plant cells

Question 92

What is the composition of the middle lamella in plant cells?

Answer 92

The middle lamella is - rich in pectins (negatively charged polysaccharides) - Ca2+ & Mg2+, and it attracts water to make a gel

Question 93

What is the function of the middle lamella in plant cells?

Answer 93

- provide mechanical support to the cells - glue adjacent cells together - which helps to maintain the structural integrity of the plant tissue

Question 94

Why are pectins important in the middle lamella?

Answer 94

Pectins are important in the middle lamella because they are negatively charged and can bind to positively charged ions such as Ca2+ and Mg2+, which helps to stabilize the structure of the cell wall and the connections between adjacent cells.

Question 95

Why are plasmodesmata necessary in plant cells? Answer: Plant cells have tough cell walls that create barriers to cell-to-cell communication, so plasmodesmata are necessary for intercellular communication.

Question 96

What are desmotubules in plasmodesmata? Answer: Desmotubules are membrane-lined bridges that link the endoplasmic reticulum (ER) of adjacent plant cells through plasmodesmata.

Question 97

What is the symplast in plant cells? Answer: The symplast is the continuous cytoplasmic network formed by the connection of adjacent plant cells through plasmodesmata.

Question 98

How many plasmodesmata can a plant cell have? Answer: A plant cell can have thousands of plasmodesmata.

Question 99

What is the function of plasmodesmata? Answer: Plasmodesmata act as a passageway for small molecules, such as metabolites, ions, hormones, and signaling molecules, to move between adjacent plant cells, enabling cell-to-cell communication and coordination.

Question 100

Tissues - Four general types of animal tissue Epithelial tissue Cells joined together forming continuous sheets to cover or line body surfaces Connective tissue Support body or connect tissues Nervous tissue Receives, generates and conducts electrical signals Muscle tissue Generates force that facilitates movement

Question 101

Tissues - Three types of plant tissue Dermal tissue Covering on various plant parts Ground tissue Most of a plant’s body with a variety of functions - parenchyma, collenchyma, and sclerenchyma Vascular tissue Form interconnected conducting vessels for water and nutrients - xylem and phloem