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FUNDAMENTALS OF MEDICINE > CELL AND TISSUE STRUCTURE > Flashcards

CELL AND TISSUE STRUCTURE Flashcards

1
Q

Why is there compartmentalization in cell structures?

A

The division of labour increases efficiency and complexity which allows for greater function.

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2
Q

What is function of a nucleus?

A
  1. Storage of DNA
  2. Expression of DNA (Production of RNA/proteins)
  3. Replication of DNA
  4. Regulates all cell functions
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3
Q

What is chromatin?

A

Chromatin is a substance within a chromosome consisting of DNA and protein.

  • The DNA carries the cell’s genetic instructions
  • The major proteins in chromatin are histones, which help package the DNA in a compact form that fits in the cell nucleus
  • Changes in chromatin structure are associated with DNA replication and gene expression
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4
Q

What is a nuclear envelope?

A

The nuclear envelope (NE) is a highly regulated membrane barrier that separates the nucleus from the cytoplasm in eukaryotic cells. It contains a large number of different proteins that have been implicated in chromatin organization and gene regulation.

  • Surrounded by a double membrane continuous with the ER
  • Contains nuclear pores that allowed controlled transport of material in and out of the nucleus
  • The nuclear lamina is the inner layer and is involved in DNA replication and cell division
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5
Q

Which is only cell type to lack a nucleus?

A

Prokaryotes

  • Unicellular organism
  • Comes before eukaryotes
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6
Q

What are nuclear pores?

A

Large protein complexes that span the double membrane of the nuclear envelope
-Control what goes in and out of the cell (Ribosomal RNA, messenger RNA, proteins, carbohydrates)

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7
Q

What are laminopathies?

A

A group of rare genetic disorders caused by mutations in genes encoding proteins of the nuclear lamina.
-Example: Emery-Driefuss Muscular dystrophy and Progeria Syndrome

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8
Q

What is Progeria Syndrome?

A

Hutchinson-Gilford Progeria Syndrome is premature aging
-As the nuclear lamina normally provides support for organizing chromatin during mitosis, weakening of the nuclear lamina limits the ability of the cell to divide

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9
Q

What is the nucleolus?

A

The nucleolus is a region found within the cell nucleus that is concerned with producing and assembling the cell’s ribosomes. Following assembly, ribosomes are transported to the cell cytoplasm where they serve as the sites for protein synthesis.

  • Generally a dense darker sphere in the nucleus
  • Composed of nucleolar organizing regions made up of specific chromosomal segments
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10
Q

What is Heterochromatin?

A

Tightly packed/condensed DNA

  • Transcriptionally inactive (repressed)
  • Plays a vital role in sustaining stable structure of specialized chromosomal regions with repetitive DNA, such as centromeres and telomeres.
  • Loss of integrity in these chromosomal areas can lead to detrimental effects and drive cancer development.
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11
Q

What is Euchromatin?

A

Less dense, open DNA

  • Lightly packed form of chromatin (DNA, RNA, and protein) that is enriched in genes, and is often (but not always) under active transcription of DNA to mRNA products
  • Comprises the most active portion of the genome within the cell nucleus. 92% of the human genome is euchromatic
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12
Q

What are ribosomes?

A

A ribosome is a cellular particle made of RNA and protein that serves as the site for protein synthesis in the cell. The ribosome reads the sequence of the messenger RNA (mRNA) and, using the genetic code, translates the sequence of RNA bases into a sequence of amino acids (Polypeptide chains)

  • Located either free in the cytoplasm or bound to the surface of the RER or nuclear envelope
  • Made up of 2 subunits (60s and 40s)
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13
Q

What is the endoplasmic reticulum?

A

Composed of a membrane that is continuous with the nuclear envelope
-Forms folds of membranes called cisternae within which polypeptides are processed further

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14
Q

What are the two types of endoplasmic reticulum?

A
  1. Rough ER:
    - Covered in ribosomes on the outer surface
    - Polypeptide chains produced by ribosomes enter immediately where they are folded into their specific 3D structures
    - Most proteins are tagged, a common tag is the addition of a carbohydrate, glycosylation
    - Almost all cellular and secretory proteins are processed by the RER
  2. Smooth ER:
    - Absence of ribosomes on the surface
    - Have specific functions in different cell types (In the muscles, SER stores calcium for contraction)
    - Important for the synthesis of carbohydrates and lipids within the cell
    - Can breakdown lipids and synthesize new fatty acids
    - Contains detoxifying enzymes in kidney and liver cells
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15
Q

What are the consequences of incorrect protein folding?

A

Gives rise to a variety of diseases

  • Alzheimer’s
  • Parkinson’s
  • Sickle Cell disease
  • Cystic fibrosis
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16
Q

What is the Golgi apparatus?

A

Stacks membranes that modify and package proteins for transport to different areas of the cells or into secretory vesicles to be released outside of the cell

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17
Q

What is exocytosis?

A

Process by which cells release proteins into the extracellular environment through secretory vesicles
-Can be done through 3 pathways

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18
Q

What are the 3 pathways of exocytosis?

A
  1. Consecutive secretion:
    - Example: The release of extracellular matrix proteins
  2. Regulated secretion:
    - Example: Release of hormones from endocrine cells
  3. Lysosomal secretion
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19
Q

What are lysosomes?

A

Membrane bound vesicles containing digestive enzymes

  • Produced by the golgi apparatus
  • Enzymes present breakdown food or other organelles (autophagy), breakdown of invading organisms (Bacteria, fungi) and the breakdown of the cell itself (autolysis)
20
Q

What are lysosomal storage diseases?

A

Defects in Lysosomes caused by genetic mutations, inborn errors of metabolism characterized by the accumulation of substrates in excess in various organs’ cells
-Tay Sachs disease: caused by failure to break down lipids causing the death of neurons in the brain and the spinal cord, HEXA gene mutation

21
Q

What is endocytosis?

A

The process by which substances/organisms enter cells surrounded by a membrane formed from the internal budding off of cell membrane
-It is an energy-consuming process

22
Q

What are the 3 types of endocytosis?

A
  1. Phagocytosis: Cell eating
  2. Pinocytosis: Cell drinking
  3. Receptor mediated or clathrin mediated
23
Q

What is clathrin?

A

Clathrin is a protein that plays a major role in the formation of coated vesicles

24
Q

What are peroxisomes?

A

Membrane bound vesicles containing a number of catalytic enzymes responsible mainly for the breakdown of fatty acids

  • Originates from the RER
  • Contains the enzyme catalase needed for the breakdown of hydrogen peroxide which is common byproduct of other enzyme activity
  • Contains detoxifying enzymes in the liver and kidney
25
Q

What are peroxisomal disorders?

A

Group of inherited rare metabolic diseases resulting from malfunctioning peroxisomes or their enzyme, resulting in an accumulation of Hydrogen Peroxide
-Zellweger syndrome

26
Q

What is the role of the mitochondria?

A

Responsible for energy production of the cell

  • Has two double layered membranes and folds called cristae
  • Has its own mitochondrial DNA which codes for some (not all) protein functioning
  • Important during initiation of apoptosis (programmed cell death)
  • Mitochondrial diseases mostly affect the muscle and nervous systems. which are the high energy demand systems
27
Q

What is the cytoskeleton?

A

Network of protein structures that maintain the physical integrity of the cell and allow for transport and movement of organelles and vesicles throughout the cell
-Allows flexibility and movement within the cell but also provides mechanical support and rigidity

28
Q

What is the cytoskeleton made up of?

A
  1. Microfilaments
    - Made of of actin (the thinnest microfilament in the cell
    - Mechanically supports the cell (stress fibres)
    - Allows movement of organelles
    - Allow cell movement together with myosin by forming filopodia (cytokinesis)
    - In muscles, allow contraction together with myosin
    - Actin myopathies: Floppy babies, hypotonia, decrease muscle tone
  2. Intermediate filaments
    - Mainly involved in providing tensile strength whilst maintaining flexibility of the cell
    - Different cell types have different intermediate filaments made up of different protein components (connective tissue (vimentin), nerves (neurofilaments), muscle (desmin), skin (Keratin)
    - Epidermolysis Bulbosa is a disease associated with keratin, easy blistering of the skin
  3. Microtubules
    - Large tubular structures which are generally hollow and made up of the protein tubulin (alpha and beta dimers)
    - Scaffolding function: organelles and vesicles can move along
    - Forms the framework of the mitotic spindle required for cell division (can be a target for cancer chemotherapy)
    - May also act as cilia or flagella in specialized cells to propel/move cells `
29
Q

What is the plasma membrane?

A

Forms the outside boundary of cells and also internal vesicles and some organelles

  • Phospholipid bilayer with internal hydrophobic molecules and external hydrophilic molecules
  • Can be highly complicated and dynamic
  • Contains various proteins that either attach to the membrane or span part of/completely the membrane (channel proteins)
30
Q

What are the functions of the plasma membrane?

A
  • Protection
  • Communication (Receptors, antigen-presenting complexes)
  • Permeability (Channels and pores)
  • Identification (immune checks)
  • Cell adhesion
  • Anchors cytoskeleton
  • Interaction with ECM
31
Q

What is the basement membrane?

A

A layer of extracellular matrix secreted by the epithelial cells
-Made up of Type IV collagen, laminin and a heparan sulfate proteoglycan

32
Q

Functions of the basement membrane

A
  • Structural support for the surrounding tissues
  • Relays functional messages
  • Acts as a transit for various growth factors
  • Serves as a physical barrier between epithelium and underlying connective tissue
  • Molecular filter
  • Controls cell movement along the membrane
  • Anchorage to the epithelia
33
Q

What is epithelial mesenchymal transition?

A

Malignant cancers undergo EMT by disrupting the ECM and breaking through the basement membrane to infiltrate the nearby tissues and access the blood supply.

34
Q

Functions of tight junctions

A
  • Holds cells together
  • Physical barrier between the outer side of cells and the inner side (important for selective transportation and osmotic balance)
  • Prevents passage of ions and molecules between adjacent cells
  • Prevents passage of bacteria and viruses from the lumen into the interstitial spaces
  • Alzheimer’s, Parkinson’s, multiple sclerosis, stroke and epilepsy disrupt the tight junctions
35
Q

What are adherens junctions?

A

A cell junction whose cytoplasmic face is linked to the actin cytoskeleton

  • Found in epithelia and endothelial cells
  • Located more basally than tight junctions
  • Cadherin forms the core by adhering tightly to each other in the presence of calcium and bind catenin on the cytoplasmic side which connects them to the actin filaments of the cytoskeletons
  • Adds robustness and plasticity to cells
  • Helps cells stick together strongly but also helps during wound healing to facilitate cell contact
36
Q

What are desmosomes?

A

Specialized adhesive protein complexes that localize to intercellular junctions and are responsible for maintaining the mechanical integrity of tissues.

  • Connects to keratin microfilaments of the cytoskeleton through specialized plaques on the inner side of the cell membrane
  • They are randomly arranged spots on the lateral sides of plasma membranes
  • Provide strong attachment between cells in tissues that have high mechanical stress such as cardiac tissues, bladder, intestinal mucosa and epithelium
37
Q

What are diseases of desmosomes?

A
  • Arrhythmogenic right ventricular cardiomyopathy is a disease caused by mutations in desmoglein gene resulting in defective desmosomes and can cause sudden death in young man.
  • Staphylococcal scalded-skin syndrome are the result of bacterial proteases directed at desmosomal cadherins and result in epidermal blisters
  • Pemphigus vulgaris: autoimmune disease that attacks desmosomes causing blisters
38
Q

What are Gap Junctions?

A

Specialized intercellular connection between a multitude of cell types

  • Forms direct connections between the cytoplasms of 2 adjacent cells, allowing the regulated passage of molecules and ions between cells
  • Can be used to establish chemical and electrical gradients between cells (electrical conduction in cardiac muscle cells)
  • Made up of complexes of proteins called connexin
39
Q

What are Pseudopodia?

A

Temporary cytoplasm filled projection of the cell membrane

  • Movement is caused by the rearrangement of the cytoskeleton (Extension+reassembly of actin and contraction of myosin)
  • Used for motility and ingestion (Phagocytosis)
40
Q

What are lamellipodia?

A

Lamellipodia are flat, broad protrusions that allow a cell to move forward and make contact with other cells and their environment.
-Movements occur due to ATP –driven polymerization
of actin filaments.

41
Q

What are filopodia?

A

Filopodia are long thin protrusions that extend several micrometers ahead of the cells and are used to explore and sense the nearby environment to guide the cell and make contact with other cells.
-Movements occur due to ATP –driven polymerization
-Tumour cells tend to produce many filopodia to sense and invade
their immediate environment.

42
Q

What are microvilli?

A

Small extensions of the cell surface of absorptive and secretory epithelial cells, such as kidney and intestinal cells. (Brush Border)

  • Increases the surface area of cells by approximately 600 fold, for absorption and secretion
  • Often have enzymes that aid their function e.g., enzymes to help hydrolyze carbohydrates are present on microvilli in intestinal epithelial cells
  • Covered with glycocalyx consisting of peripheral glycoproteins that can attach themselves to a membrane. This layer may be used to aid binding of substances needed for uptake, to adhere nutrients or as protection against harmful elements. It can be another location for functional enzymes to be localized.
  • Structure is maintained by actin filaments
43
Q

What are diseases associated with microvilli?

A
  1. Infections (Escherichia Coli), Celiac Disease and Microvillus Inclusion Disease (chronic diarrhea)
    - Disrupts the structure of the epithelial layer of the small intestine
    - Malabsorption of nutrients and persistent osmotic diarrhea, often accompanied by fever and failure to thrive
  2. Toxins
    - Destruction of microvilli, tight junctions resulting in inhibition of water reabsorption
  3. Congenital lack of microvilli
    - Microvillus atrophy, a rare, usually fatal condition found in newborn babies
44
Q

What are cilia?

A

Slender protuberances that project from the much larger cell body

  • Divided into motile and non-motile
  • Depends on the arrangement of microtubules within the cilium
  • Non-motile: For sensory surfaces (ears, mechanoreceptors)
  • Motile: Trachea (moving mucus), fallopian tubes (moving ova)
45
Q

What pathologies of the Cilia?

A

Bardet-Biedl Syndrome

  • Affects numerous developmental signaling pathways essential to cellular development
  • Patients with BBS can experience problems with obesity, specifically with fat deposition along the abdomen. They often also suffer from intellectual impairments.

FUNDAMENTALS OF MEDICINE (8 decks)

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