week 2 Flashcards
(97 cards)
1
Q
what are the qualities of cellular membranes?
A
- Membrane Composition And Structure
- Cell Recognition and Adhesion
- Passive Processes of Membrane Transport
- Active Transport
- Endocytosis and Exocytosis
- Membranes Are Dynamic
2
Q
what is the phospholipid bilayer and how is it structured?
A
- Bilayered, dynamic structures that:
- Perform vital physiological roles
- Form boundaries between cells and their environments
- Regulate movement of molecules into and out of cells
- The lipid portion provides a barrier for water-soluble molecules.
- Lipids are like the water of a lake in which proteins “float.”This general design is called the fluid mosaic model.
- Membrane proteins are embedded in the lipid bilayer.
- Carbohydrates attach to lipid or protein molecules on the membrane, generally on the outer surface
3
Q
what is the phospholipid bilayer made out of?
A
A Phospholipid Bilayer Separates Two Aqueous Regions
Hydrophilic Region (phosphate group)
Hydrophobic Region(fatty acids)
4
Q
what is the structure of integral membrane proteins?
A
Integral membrane proteins have hydrophobic regions of amino acids that penetrate or entirely cross the phospholipid bilayer
5
Q
what is the structure of transmembrane proteins?
A
Transmembrane proteins have a specific orientation,showing different “faces” on the two sides of the membrane
6
Q
what is the structure of peripheral membrane proteins?
A
Peripheral membrane proteins lack hydrophobic regions and are not embedded in the bilayer.
7
Q
how do proteins and lipids move around in the membrane?
A
- Some of the proteins and lipids can move around in the membrane.
- Experiments have demonstrated that when two cells are fused,a single continuous membrane forms around both cells and membrane proteins distribute themselves uniformly around this membrane.
8
Q
why can only some lipids and proteins move around in the membrane?
A
- Some proteins are restricted in movement because they are anchored to components of the cytoskeleton or are trapped within regions of lipid rafts
- This causes an unequal distribution of proteins,allowing for specialization of certain regions of the cell membrane
9
Q
what is different between lipid rafts in the membrane bilayer and lipid rafts in the plasma membrane?
A
Lipid rafts are more ordered and tightly packed than the surrounding bilayer but float freely in the membrane bilayer. They generally contain 3 to 5 times more cholesterol than the plasma membrane
10
Q
What are carbohydrates associated with in some cell membranes?
A
In cell membranes, carbohydrates are often found attached to the outer surface, where they are linked to proteins and lipids, forming structures known as glycoproteins and glycolipids. These carbohydrate complexes play a crucial role in cell recognition, communication, and adhesion processes. and therefore are associated with their external surfaces
11
Q
In some cell membranes, carbohydrates are associated with their external surfaces.
A
A carbohydrate-bound lipid is called a glycolipid.
12
Q
How are most of the carbohydrates in the membrane bonded?
A
Most of the carbohydrates in the membrane are covalently bonded to proteins, forming glycoproteins.
13
Q
describe the rate of diffusion in membranes?
A
- Diffusion over large distances is very slow.
- In a solution, diffusion rates are determined by temperature, size of the molecule, electrical charge of the molecule, and concentration gradient.
- The insertion of a biological membrane affects the movement of chemicals in solution according to the membrane’s properties. It may be permeable to some molecules and impermeable to others.
14
Q
What is the function of plasma membrane glycoproteins?
A
Plasma membrane glycoproteins enable cells to be recognized by other cells and proteins.
15
Q
What is homotypic binding in cell recognition?
A
Homotypic binding refers to the type of cell adhesion where identical molecules on the surface of two cells bind to each other. This is often mediated by cellular adhesion molecules of the same kind, which can lead to cell aggregation.
16
Q
What is heterotypic binding in cell recognition?
A
Heterotypic binding involves the binding of different molecules on the surfaces of two cells. These different molecules, often complementary, can belong to different mating types or cell types, enabling diverse interactions and recognition processes.
17
Q
where are cell junctions located?
A
Specialized cell junctions form between cells in a tissue
18
Q
in which cell type are cell junctions most common in?
A
Cell junctions are especially abundant in epithelial tissues
19
Q
how many types of cell junctions are there in animals?
A
Animals have three types of cell junctions:
tight junctions, desmosomes, and gap junctions
20
Q
what are tight junctions?
A
- Tight junctions are specialized structures at the plasma membrane that link adjacent epithelial cells.
- They have two primary functions:
- To restrict the migration of membrane proteins and phospholipids from one region of the cell to another
- To prevent substances from moving through the intercellular space
21
Q
what is a desmosome cell junction?
A
- Desmosomes act like spot welds on adjacent cells, holding them together.
- Desmosomes have dense plaques that are attached both to cytoplasmic fibers and to membrane cell adhesion proteins (intermediate filaments of the cytoskeleton).
- The membrane cell adhesion proteins bind to the proteins of an adjacent cell.
22
Q
what is a gap junctions function?
A
- Gap junctions are connections that facilitate communication between cells.
- Gap junctions are made up of specialized protein channels called connexons.
- Connexons span the plasma membranes of two adjacent cells and protrude from them slightly.
- Connexons are made of proteins called connexins, which snap together to generate a pore
23
Q
what is diffusion?
A
Diffusion is the process of random movement toward the state of equilibrium
24
Q
how do particles move in diffusion?
A
Although individual particles move randomly, in diffusion the net movement is directional, from regions of greater concentrations to regions of lesser concentrations, until equilibrium is reached
25
zhow do molecules move through the lipid bilayer?
* Small molecules can move across the lipid bilayer by simple diffusion.
* The more lipid-soluble the molecule, the more rapidly it diffuses.
* An exception to this is water, which can pass through the lipid bilayer more readily than its lipid solubility would predict.
* Polar and charged molecules such as amino acids, sugars, andions do not pass readily across the lipid bilayer.
26
what is osmosis?
* Osmosis is the diffusion of water across membranes.
* Osmosis is a completely passive process and requires no metabolic energy.
* Water will diffuse from a region of its higher concentration (low concentration of solutes) to a region of its lower concentration(higher concentration of solutes).
27
what particles cannot diffuse through the lipid bilayers?
Passive Processes of Membrane Transport* Polar and charged substances do not diffuse across lipid bilayers.
* One way for these important raw materials to enter cells is through the process of facilitated diffusion.
28
what does facilitated diffusion depend on?
* Facilitated diffusion depends on two types of membrane proteins: channel proteins and carrier proteins
29
where are ion channels found snd what are their properties?
These are found in the membrane of nearly all cells
.* 106 ions per sec or more.
* Can be gated
* Potassium ion channel activated by changes in voltage across the membrane
30
what is active transport and how does it work?
* In contrast to diffusion, active transport requires the expenditure of energy.
* Ions or molecules are moved across the membrane against the concentration gradient.
* ATP is the energy currency used either directly or indirectly to achieve active transport.
31
what molecules can use the primary active transport system?
Only cations such as sodium, potassium and calcium use primary active transport system
32
what is the secondary active transport system?
* Uses established gradients to move substances.
* Uses ATP to establish theion gradient.
* The gradient is then used to move a substance, as described for the symportand antiport systems.
* An example is the symport system found in intestinal cells, which moves glucose up its concentration gradient, while moving sodium ions down their ion concentration gradient.
33
what are some examples of endocytosis?
* Phagocytosis
* Pinocytosis
* receptor-mediated endocytosis
34
what happens during phagocytosis?
* During phagocytosis,which involves the largest vesicles, entire cells can be engulfed.
* Phagocytosis is common among unicellular protists.
* White blood cells in humans and other animals also use phagocytosis to defend the body against invading foreign cells
35
what is pinocytosis?
* Pinocytosis, which means “cellular drinking,” involves vesicle formation as well, but the vesicles are far smaller.
* Dissolved substances and fluids are brought into the cell.
* In humans, the single layer of cells separating blood capillaries from surrounding tissue uses pinocytotic vesicles to acquire fluids from the blood
36
what is receptor mediated endocytosis?
* Receptor-mediated endocytosis is similar to pinocytosis, but it is highly specific
* Receptor proteins are exposed on the outside of the cell in regions called coated pits. Clathrin molecules form the “coat” of the pits
37
what is exocytosis?
* Exocytosis is the process by which materials packaged in vesicles are secreted from the cell.
* The vesicle membranes fuse with the plasma membrane and release vesicle contents (wastes, enzymes, hormones, etc.) into the environment
38
what are the functions of membranes?
* Information processing
* Energy transformation
- The inner mitochondrial membrane helps convert the energy of fuel molecules to the energy in ATP.
- The thylakoid membranes of chloroplasts are involved in the conversion of light energy in photosynthesis
* Membranes are involved in organizing chemical reactions,allowing them to proceed rapidly and efficiently
39
what do prokaryotic cells never have?
a nucleus
40
how do prokaryotes divide?
Prokaryotes divide by fission
41
Describe the steps of prokaryotic cell division.
Initially, the prokaryotic cell's singular circular chromosome replicates. The two resulting DNA molecules attach to distinct points on the plasma membrane.
With cell growth, the membrane is added between these points, separating the DNA. Cytokinesis then occurs, cleaving the cell into two identical cells, each with a complete chromosome.
42
how do eukaryotic cells divide?
Eukaryotic cells divide by mitosis or meiosis
Eukaryotes have a nucleus, which must replicateand, with few exceptions, divide during celldivision
43
how many chromosomes do eukaryotic cells have?
they usually hae many chromosomes
44
describe the structure of a nucleus
Structure of Nucleus
* Usually the largest organelle in the cell
* Contains most of the cell’s genetic material(DNA)
* Replication of DNA and the first steps in decoding it for protein production take place in the nucleus
has nuclear pores for movement of RNA during protein synthesis
has a nucleolus
45
what surrounds the nuclear pores?
8 Large protein granules surround each pore
46
what molecules can pass through the nuclear envelope?
From nucleus:
- RNA
- ribosomal proteins
To nucleus
-proteins (DNA polymerase and lamins),
-carbohydrates,
-signalling molecules and lipids
47
how are things organised within the nucleus?
* Each nucleus ~ 5 - 10 μmin diameter
* Nucleolus can take up to 25% of its volume
* 2 m DNA in each nucleus
* Roughly 1/266,667 times‘shorter’
48
what are chromosomes?
* In the nucleus the DNA molecule is packaged into thread-like structures called chromosomes.
* Chromosomes are not visible if the cell is not dividing.
49
what is a centromere in a chromosome?
Each chromosome has a constriction point called the centromere, which divides the chromosome into two sections, or “arms”.
* The short arm is labelled the “p arm”. The long arm is labelled the “q arm”.
* The location of the centromere on each chromosome gives the chromosome its characteristic shape, and can be used to help describe the location of specific genes
50
how many pairs of chromosomes do humans have?
Humans have 46 (22 pairsplus two non-paired sexchromosomes)
51
how many base pairs are in a chromosome
One chromosome can have as few as 50 million base pairs or as many as 250 million base pairs
52
why is human DNA different?
* Over 99% of our DNA sequence is the same as other humans
53
how do we make chromosomal DNA smaller?
* Proteins called histones compact chromosomal DNA into the microscopic space of the eukaryotic nucleus
* Resulting DNA-protein complex is called chromatin
* Odd but - proteins are added to DNA to make it more compact
* This coiling requires work, and energy is needed to perform work
* Within the nucleus, histones provide the energy (mainly inthe form of electrostatic interactions) to fold DNA
54
what are histones?
* Histones are a family of small, positively charged protein stermed H1, H2A,H2B, H3, and H4
55
what charge does DNA have?
DNA is negatively charged, due to the phosphate groups in its phosphate-sugar backbone
56
what are nucleosomes?
The basic repeating structural and functional unit of chromatin is the nucleosome, which contains nine histone proteins and about 166 base pairs of DNA
57
how does packaging DNA into chromosomes affect DNA?
* Packaging DNA into nucleosomes shortens the fibre length about sevenfold
* Piece of DNA 1 meter long will become a "string-of-beads"chromatin fiber just 14 cm long
* Chromatin is further coiled into an even shorter, thicker fiber termed the "30-nm fiber“,because it is approximately 30nm in diameter
* The 30-nanometer fiber may be highly irregular and not quite the uniform structure depicted in textbooks
58
what is chromatin?
* Chromatin is the name given to the mixture of DNA, Histones and other proteins that make up Chromosomes
* It is divided between heterochromatin (condensed) and euchromatin (extended) forms.
* The functions of chromatin are
- to package DNA into a smaller volume to fit in the cell,
- to strengthen the DNA to allow mitosis and meiosis,
- to control gene expression and DNA replication
59
what do transcription and replication require to access the DNA template?
Both require the two strands of DNA to separate temporarily to allow polymerases access to the DNA template
60
How do cells make chromatin accessible for DNA replication and transcription, and what are the two major mechanisms involved?
* to overcome the barriers posed by folding.
* The two major mechanisms for making chromatin more accessible are the enzymatic modification of histones and the displacement of histones by chromatin remodeling complexes.
* these processes are reversible.
61
what happens during prometaphase?
Nuclear envelope breaks down and microtubules attach to chromosome
62
what is metaphase
Thick, coiled chromosomes are lined up in the centre of the cellon the metaphase plate. Spindle fibers are attached to the chromosomes
63
what is the difference between the prokaryotic and the eukaryotic cytoskeleton?
They do have structural proteins which allow them to maintain shapes other than spherical.
They also have proteins which form a constricting band around the cell when dividing
64
how many protein molecules and types exist in a eukaryotic cell? also explain how they are stored and why they are stored in this way
* Contains ~ a billion protein molecules
* About 10,000 different protein types
* Most need to be highly organised!!
– Complexes of protein molecules
– Contained within organelles
– Even higher level of organisation created and maintained by cytoskeleton
* Enables cell to behave like a living city with communication and transport between all the different areas
65
what is the function of polymerisation of cytoskeleton components in an eukaryotic cell?
to allow organisation via cytoskeleton protein molecules.
Each of the major types of cytoskeleton proteins are formed from thousands of identical subunits which form in a linear manner.
66
67
What is the structural similarity among microtubules, microfilaments, and intermediate filaments?
ll three types of cytoskeletal proteins form helical polymers, each with a distinct function within the cell's structure.
68
How do cytoskeletal proteins contribute to cell shape and strength?
interlink the filaments, connect them to other cell partsza
regulate their assembly
and provide motor functions for organelle movement or filament relocation
69
what are the functions of microtubules?
Microtubules provide a rigid intracellular skeleton for some cells, and they function as tracks that some motor proteins can move along in the cell.
70
how are microtubules formed?
Formed from polymerization of tubulin monomers
71
What are microtubules and how are they polarized?
Microtubules are polar structures within the cell composed of tubulin subunits. They have two ends: the plus end, which is capable of rapid growth, and the minus end, which can lose subunits if not stabilized. The plus end usually has β-subunits exposed, while the minus end has α-subunits exposed.
72
How are microtubules stabilized and where is elongation typically observed?
Microtubules are stabilized by embedding in the centrosome, which is typically located next to the nucleus at the cell's center. Elongation of microtubules generally occurs only from the plus (+) end.
73
What components are responsible for microtubule nucleation and anchoring?
he pericentriolar material (PCM) comprises the proteins responsible for microtubule nucleation and anchoring at the MTOC.
74
what is the structural composition of centrioles?
Centrioles, which are part of the centrosome, have a characteristic 9-triplet microtubule assembly.
75
What is the main microtubule organizing center (MTOC) in animal cells and what is its role in the cell?
The centrosome serves as the main microtubule organizing center (MTOC) in animal cells. It plays a key role in organizing the microtubule network during mitosis, although it is not essential for the process.
76
Describe the dynamics of microtubules in relation to the centrosome.
he centrosome serves as the nucleation point for several hundred microtubules, which grow outward from it. These microtubules are highly dynamic structures, characterized by their constant growth and shrinkage, particularly at the plus end.
77
What is a visible use of microtubules in the animal kingdom, specifically related to fish scales?
Microtubules play a role in the color change of fish scales, enabling the fish to adapt to different environments. This is achieved through large flat cells that contain granules, whose color varies with the species. These granules are attached to microtubules and can either aggregate in the center of the cell or spread out within the cytoplasm. The movement of these granules, controlled by the fish through changes in cAMP levels, facilitates the change in skin color.
78
How are microtubules affected by the drugs colchicine and taxol?
Microtubules are sensitive to certain drugs, which can drastically alter their behavior. Colchicine binds to individual tubulin molecules, inhibiting their polymerization into microtubules and thereby preventing spindle formation and cell division. On the other hand, Taxol has the opposite effect; it stabilizes microtubules by binding to them and preventing their depolymerization.
79
How do motor proteins interact with the microtubule network?
Motor proteins use the microtubule network as a scaffold to move and position organelles within the cell. They are powered by the energy released from repeated cycles of ATP hydrolysis, which allows them to travel along microtubules or actin filaments. Different motor proteins are designed to move in specific directions along these filaments.
80
What are the two families of motor proteins associated with microtubules and in which direction do they move?
kinesins move towards the cell edge aka the plus end and dyneins move towards the minus end (the centrosome)
81
What are the functions of the Kinesin family of proteins and what is a common misconception about them?
The Kinesin family is not a single protein but a group with diverse roles in the cell, including organelle movement, transport of RNAs and proteins, assembly of cilia and flagella, involvement in signaling pathways, and crucial functions in mitotic spindle formation and chromosome movement during cell division.
82
What are cilia and flagella and how are they structurally composed?
Cilia and flagella are common locomotory appendages of cells composed of microtubules. Flagella are typically longer and fewer in number, with cells usually having one to eight. Cilia are shorter but much more numerous, with hundreds often present on a single cell.
83
describe the microtubule arrangement in cilia and flagella and the structure at their base.
The microtubules in cilia and flagella are arranged in a 9 + 2 pattern, which consists of nine pairs of microtubules forming a ring around a central pair. At the base of each flagellum or cilium is a basal body, into which the nine pairs of microtubules extend.
84
What are microfilaments and how do they contribute to cell structure and movement?
Microfilaments are composed of the protein actin and can form as single filaments, bundles, or networks. They are crucial for determining and stabilizing cell shape, enabling both whole-cell and partial-cell movement, and are involved in processes like cytoplasmic streaming and the formation of pseudopodia.
85
How do non-pigmented fish scale cells demonstrate the roles of actin filaments?
In non-pigmented fish scale cells, which can rapidly migrate in culture, intermediate filaments and microtubules are found primarily at the trailing edge around the cell nucleus. The flattened, leading edge is rich in actin filaments. While depolarization of microtubules does not affect cell migration, disruption of actin filaments immediately stops it, highlighting the critical role of actin in cell motility.
86
How does Listeria Monocytogenes move within and between cells?
Listeria Monocytogenes enters cells via phagocytosis, escapes the phagosome by breaking down its membrane, and then uses one region on its surface to nucleate actin filaments. As these filaments grow, they push the bacterium forward, creating a micro-spike in the cell membrane with the bacterium at the tip. The bacterium can then be engulfed by neighboring cells, allowing it to transfer directly to a new cell without being exposed to the immune system.
87
What was the first motor protein to be discovered and what is its function and diversity?
myosin was the first motor protein to be discovered. It is distinct from Kinesins and Dyneins because it moves along actin filaments. In skeletal muscle, it is a major component of the contractile mechanism (tightening and relaxing muscles) and is abundant.
Myosins in non-muscle cells have similar motor domains but different adaptor domains (different attachment parts), allowing them to bind to various cell structures/components.
88
How do different filament types coordinate within living cells, and what is an example of their cooperation?
in living cells, the three types of filaments (actin filaments, microtubules, and intermediate filaments) are interconnected, and their functions are coordinated for efficient cellular operation.
An example of this coordination is seen in cytotoxic T cells, where actin filaments and microtubules work together to polarize the cell, enabling it to respond effectively to pathogens.
89
What are the steps involved in the polarization of a cell?
Polarization begins when the plasma membrane detects a difference on one side of the cell, leading to a transmembrane signal. This signal triggers the reorganization of the actin cortex in a localized area beneath the affected membrane. The centrosome then moves towards that part of the cell, possibly by pulling on microtubules, and repositions the internal membrane systems. The result is a cell with a strong directional focus, ready to interact with its environment or target cells.
90
What is the role of cytotoxic T cells in the immune system, and how do they recognize infected host cells?
Cytotoxic T cells are critical components of the immune system that specialize in killing infected host cells. They recognize infected cells through proteins on the surface of the host cell that are identified by the T cell receptor (TCR). Upon recognition, the TCR sends a signal that leads to the reorganization of the T cell's cytoskeleton to prepare for an attack.
91
Describe the cytoskeletal changes in a cytotoxic T cell upon recognizing an infected cell.
proteins associated with actin filaments reorganize beneath the zone of contact, the centrosome and its microtubules reorient towards this zone, and
the Golgi apparatus positions itself directly underneath.
These rearrangements focus the cell's killing machinery, which is associated with secretion from the Golgi, directly at the target cell to effectively deliver lethal hit.
92
How is the process of cell polarization initiated?
Cell polarization is initiated when the plasma membrane senses an asymmetry, leading to a transmembrane signal. This differential signal is the first step in reorganizing the cell's structure for a directed response.
93
What are the cellular changes during polarization?
Upon receiving a polarization signal, the actin cortex underneath the membrane reorganizes locally. The centrosome moves toward this area, potentially using microtubules, which facilitates the repositioning of internal membrane systems. Consequently, the cell develops a strong directional focus to effectively interact with its environment or engage target cells.
94
How do intermediate filament protein monomers differ from tubulin and actin, and what structure do they form?
Unlike tubulin and actin, which are globular proteins, intermediate filament protein monomers are elongated, fibrous molecules. These monomers form two coiled-coil dimers that associate in an antiparallel manner to create non-polarized tetrameric subunits, which are structurally the same at both ends.
*
95
What are keratins and how are they categorized in human cells and structures?
Epithelial cells contain over 20 distinct types of keratins. Additionally, there are at least 8 more types of keratins, known as hard or α-keratins, which are specific to hair and nails. These α-keratins are differentiated from the β-keratins found in feathers, which are evolutionarily distinct.
96
What function do intermediate filaments serve in cells, according to increasing evidence?
intermediate filaments, including those formed by keratins, are increasingly recognized for their role in aiding cells to resist mechanical stress. This property is vital for maintaining the integrity of tissues that are subjected to physical forces.
97
How do mutations in keratin genes affect individuals with epidermolysis bullosa simplex?
In the genetic disease epidermolysis bullosa simplex, mutations in the keratin gene in the basal layer of the epidermis disrupt the keratin network. This disruption makes the skin of sufferers extremely vulnerable to mechanical injury, leading to blistering and an increased risk of damage from physical stress.
