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Cell Biology > Cell cytoskeleton and cytoplasm ✅ > Flashcards

Cell cytoskeleton and cytoplasm ✅ Flashcards

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1
Q

What are the three major components of eukaryotic cells?

A

1) cell membranes seperate a cell from its environment, and form distinct functional compartments (eg. nucleus, mitochondria, organelles).
2) The cytoplasm surrounds the nucleus and is enclosed by the plasma membrane.
3) The membrane-limited nucleus contains the DNA

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2
Q

What does the cytoplasm hold?

A

It contains the structures and substances that decode the instructions of DNA and carry on the cell’s activities.

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3
Q

What does DNA hold?

A

The genetic code for protein synthesis and thus for all cell activities.

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4
Q

What is a different name for the plasma membrane?

A

plasmalemma

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5
Q

Where is the plasma membrane found?

A

The membrane is found in all cells. It separates the interior of the cell from the outside environment.

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6
Q

What do bacterial and plant cells have in addition to the plasma membrane?

A

a cell wall

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7
Q

Explain the biochemical component: Lipids. State examples, the most abundant forms, etc.

A

Lipids in cell membranes include: - phospholipids,
- sphingolipids,
- cholesterol.

Phospholipids are the most abundant form. They have:
- polar heads,
- non-polar tails
- arranged in a bilayer

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8
Q

Explain the biochemical component: Proteins. What percentage of the membrane are proteins? What are the two groups of proteins in membranes? State examples, the most abundant forms, etc.

A

Proteins: more than 50% of membrane weight.

Most membrane proteins are GLOBULAR and belong to one of two groups:
- Integral membrane proteins (tightly lodged in the lipid bilayer; detergents are required to extract them)
- transmembrane proteins (penetrate the entire membrane and protrude from both sides.)
- Peripheral membrane proteins

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9
Q

What are the key features of integral membrane proteins?

A
  • They are folded, (hydrophilic amino acids & membrane
    phospholipids’ phosphate groups) (hydrophobic amino acids & fatty acid tails)
  • Some protrude from only one membrane surface.
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10
Q

What are the key features of transmembrane proteins?

A
  • can be hydrophilic (allowing for the passage of water and water-soluble materials)
  • form channels and receptors
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11
Q

What do cryofracture preparations do to the plasma membrane?

A

Cryofracture preparations often split plasma membranes through the hydrophobic
region, between the ends of the phospholipids’ fatty acid tails.

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12
Q

How is the membrane divided in a cell? Where are most integral proteins located?

A
  • Most integral proteins: P (protoplasmic) face (closer to the cytoplasm).
  • the E (ectoplasmic) face, (closer to the environment) usually appears smoother.
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13
Q

What are the key features of peripheral membrane proteins?

A
  • ionically associated with the inner or outer membrane surface
  • released in high-salt solutions;
  • some are globular, some filamentous.

eg. in erythrocytes, spectrin, (on the outer membrane surface) helps maintain membrane integrity, (and ankyrin, which links spectrin to protein-3-tetramer).

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14
Q

Explain the biochemical component: Carbohydrates. What are the most abundant forms?
What is their characteristic structure?

A
  • occur on plasma membranes mainly as oligosaccharide moieties of glycoproteins and glycolipids.
  • only occur on the plasma membranes outer surface
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15
Q

What is the characteristic structure of membrane oligosaccharides? What is the surface coat called?

A
  • Membrane oligosaccharides have a characteristic BRANCHING structure and project from the cell’s outer surface, forming a surface coat called the GLYCOCALYX that participates in cell adhesion and recognition.
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16
Q

What is the name of the surface coat? What is its function?

A

GLYCOCALYX participates in cell adhesion and recognition.

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17
Q

What happens to lipid mobility when temperature decreases?

A

goes from fluid to a gel form (limited lipid mobility.

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18
Q

What happens to lipid mobility when temperature increases?

A

change of gel into a fluid –> increased lipid mobility.

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19
Q

What some examples of integral proteins?

A
  • Ion channels,
  • proton pumps,
  • G protein-coupled receptor
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20
Q

What some examples of lipid-anchored proteins?

A
  • G proteins
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21
Q

What some examples of peripheral proteins?

A
  • enzymes
  • hormones
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22
Q

What are the functions of the plasma membrane?

A

1) Physical barrier (flexible boundary, protects cellular components, supports cell structure)
2) Selective permeability (regulates entry and exit of ions)
3) electrochemical gradient (establishes electrical charge)
4) communication (receptors)

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23
Q

Explain the membrane organisation.

A
  • fluid mosaic model: “protein icebergs and lipid sea”
  • membrane asymetry=differences in chemical composition
  • phospholipid asymmetries occur.
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24
Q

Explain the membrane function of “selective permeability”.

A
  • control of substance movement across the plasma membrane
  • maintains the cell potential
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25
Q

What are the three major mechanisms by which molecules cross membranes?

A

1) simple diffusion
2) channel
3) carrier/pump

26
Q

Explain passive diffusion.

A
  • down the concentration gradient (high to low)
  • passive transport (NO ATP needed)
  • random movement
27
Q

Explain facilitated diffusion.

A
  • down the concentration gradient (high to low)
  • passive transport (NO ATP needed)
  • selective movement
  • unidirectional
28
Q

Explain active transport.

A
  • against the concentration gradient (low to high)
  • active transport (ATP NEEDED)
  • eg. sodium potassium pump
29
Q

What are the two types of active transport?

A

1) primary active transport (ATP-driven pump stores energy (direct))
2) secondary active transport (diffusion through a membrane co-transporter protein)

30
Q

Explain signal transduction.

A

The signal molecule to which a receptor specifically binds is its ligand.
The receptor transduces the signal across the membrane without the ligand entering the cell.

31
Q

What is a ligand?

A

The signal molecule to which a receptor specifically binds is its ligand.
a molecule that can bind to a receptor.

32
Q

What does signal transmission depend on?

A

the receptor class involved.

33
Q

What are the receptor classes?

A

1.LIGAND GATED (e.g., transmitter-gated) ion channels are long proteins that pass multiple times through the plasma membrane.
2.ENZYME- LINKED RECEPTORS comprise a heterogeneous group of transmembrane (typically single-pass) proteins associated with an enzyme (typically a protein kinase) or possessing kinase activity of their own (e.g., tyrosine kinase).
3. G PROTEIN-COUPLED RECEPTORS (GPCRs) comprise a family of proteins that make seven passes through the membrane.
4. STEROID HORMONE RECEPTORS family.

34
Q

Explain endocytosis.

A
  • cells engulf extracellular substances.
  • bring them into the cytoplasm in membrane-limited vesicles.
  • vesicle, pseudopodium (what encloses), (remember words)
  • active transport (REQUIRES ATP)
  • phagosomes are created
35
Q

What are the two types of endocytosis?

A

phagocytosis and pinocytosis

36
Q

Explain phagocytosis.

A

Cell engulfs insoluble substances:
- large macromolecules
- entire bacteria.

The vesicles formed are termed phagosomes.

37
Q

What are phagosomes?

A

The vesicles formed through phagocytosis.

38
Q

Explain pinocytosis.

A

The cell engulfs small amounts of fluid, (may contain a variety of solutes).

39
Q

Which vesicles are smaller? Pinocytotic vesicles or phagosomes?

A

Pinocytotic vesicles are smaller than phagosomes.

40
Q

Explain receptor-mediated endocytosis.

A
  • a cell engulfs ligands along with their surface
    receptors
  • cytoplasmic surface is covered with the
    coat protein, clathrin.
  • After further invagination, the protein, dynamin, coils around the neck of the budding vesicle
    and pinches it off to create a coated vesicle, which carries the ligand–receptor complexes
    into the cell.
  • The clathrin coat is released from the vesicle,
  • endosome binds to the naked vesicle
  • The portion with the receptors pinches off and returns to fuse with the plasma membrane.
  • products are broken down
41
Q

Explain exocytosis. How does it occur?

A

Cells use exocytosis both:
- secretion
- excretion of undigested material.

A membrane-limited vesicle or secretory granule fuses with the plasma membrane and releases its contents into the extracellular space, without disrupting the plasma membrane.

42
Q

What are the three membrane functions?

A

1) Compartmentalization
2) Spatial–temporal organization of metabolic processes.
3) Storage, transport, and secretion

43
Q

Explain compertmentalization. What does it prevent?

A
  • Membranes selectively block the passage of most water-soluble substances.
  • The cytoplasm has many membrane-limited compartments (organelles), each with different internal solute concentrations.
44
Q

What is the function of copartmentalization?

A
  • prevents the dilution of substrates in biochemical reactions,
  • protects sensitive reactions from the intrusion of extraneous substances.
45
Q

Explain “Spatial–temporal organization of metabolic processes”. What is its function

A

Some cell membranes contain ENZYMES ARRANGED IN SERIES so that intermediates in multistep metabolic processes are passed from enzyme to enzyme.

This arrangement maintains the CHRONOLOGICAL ORDDER of such processes and sets rate limits by maintaining local concentrations of intermediates.

46
Q

Explain the “Storage, transport, and secretion.” as a function of a cell membrane.

A

Substances in vesicles may be:
- kept for later use (storage),
- shuttled from one compartment to another for further processing (transport),
- expelled from the cell (secretion).

47
Q

What is the cytoplasm?

A

The cytoplasm is all of the material within a cell, enclosed by the cell membrane, except for the cell nucleus.

48
Q

What is the nucleoplasm?

A

The material inside the nucleus and contained within the nuclear membrane.

49
Q

What is the main components of the cytoplasm?

A

cytosol,
water (80%)

50
Q

What is the cytosol?

A

a gel-like substance

51
Q

Where do most cellular activities take place?

A

within the cytoplasm.

52
Q

How does the cytoplasm divide? Into what 2 groups?

A

The concentrated inner area is called the ENDOPLASM
The outer layer is called the cell CORTEX or the ECTOPLASM.

53
Q

What is a signaling activity for metabolic processes?

A

The movement of calcium ions in and out of the cytoplasm

54
Q

What is cytoplasmic streaming?

A

The movement of the cytoplasm within an animal or plant cell.

55
Q

What is the cytosol? What does it consist of? What are its functions? What is its pH?

A
  • a component of cytoplasm.
  • The cytosol consists of a variety of ions, small molecules, water (70%) and macromolecules.
  • fluid is not a homogeneous solution.
  • pH ranges from 7.0 to 7.4

FUNCTIONS:
- involved in signal transduction (b/w the cell membrane, nucleus and organelles).
- transports metabolites from their production site to other parts of the cell.
- important for cytokinesis when the cell divides in mitosis.
- The cytosol plays a role in eukaryote metabolism.

56
Q

What is the cytoskeleton? What is its function?

A
  • a mesh of filamentous elements called microtubules, microfilaments, and intermediate filaments,
  • it provides structural stability for maintaining cell shape.
  • important in cell movement
  • important in rearranging cytoplasmic components.
57
Q

What are the three cytoskeletal fillaments?

A

1) Actin filaments
2) Microtubules
3) Intermediate filaments

58
Q

What are microtubules? What are their structure? What are their function? What is critical to their function?

A
  • wall consists of TUBULIN HETERODIMERS
    (alpha and beta tubulin)
  • threadlike chains called protofilaments,

STRUCTURE?
- Each microtubule is polarized, (with a plus (+) and minus (−) end). - exist in a state of dynamic instability, undergoing abrupt changes in length through changes in the balance between
polymerization
depolymerization.

FUNCTION?
- form a network of roadways in the cell,
- deploy cytoplasmic organelles (including the ER and Golgi complex),
- shuttle vesicles from one part of the cell to another,
- move chromosomes during mitosis.

Their INSTABILITY is critical to their function.

59
Q

What are MICROFILAMENTS? What are their structure? What are their function? What is critical to their function?

A

STRUCTURE?
- thinnest cytoskeletal elements
- more flexible than microtubules
- globular actin protein monomers
- in striated muscle actin filaments associate with myosin filaments
- Actin filaments in other cells are less stable and repeatedly dissociate and reassemble.

FUNCTION?
- regulating polymerization and depolymerization,
- actin-binding proteins arrange microfilaments into the networks and bundles that carry out their many important functions.
- role in cilia and flagella

60
Q

What are INTERMEDIATE FILLAMENTS? What are their structure? What are their function? Where are they located?

A

STRUCTURE?
- ropelike
- composed of shorter threadlike protein subunits (twisted around one another to form filaments)
- protein subunits are globular
- individual proteins belong to the same family as nuclear lamins
- differ depending on the cell type.

FUNCTION?
- tensile strength and durability
- stabilise cell structure
- maintain cell shape

LOCATION:
- form a network surrounding the nucleus
- extend throughout the cytoplasm

Cell Biology (12 decks)

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