Topic 3 cells and tissues

Question 1

What are the levels of organisation?

Answer 1

atoms - molecules - Proteins - cells - tissue - organ - organ system - organism

Question 2

How can the cell interact with it’s surroundings?

Answer 2

With surface proteins such as protein channels, integral proteins etc. They can initiate reactions inside the cells, e.g. polymerization of intracellular filaments.

Question 3

What 4 different tissue types do we consist of?

Answer 3

Nervous, epithelial, muscle and connective tissue

Question 4

What is the epithelial tissue?

Answer 4

Usually one tightly packed layer of cells to form a physical barrier (e.g. inside of gut, lining of hollow organs, skin epidermis), these cells are polarized which means that the top and the bottom of the cell is different. Often have a basal membrane consisting of proteins that can attach cells.

Question 5

What is connective tissue?

Answer 5

Fat, soft padding tissue, bone, blood, tendon and cartilage. Can be dense or not dense (cartilage, have lot of extracellular matrix beneficial for dampening)

Question 6

How are muscles built up?

Answer 6

Several muscle cells fuse together to one aligned muscle. They have the same direction and the alignment is for the force to be “bigger” when they contract.

Question 7

Which tissue has a very high density of cells that fuse together with each other?

Answer 7

Muscle tissue

Question 8

Which tissue is comprised of a tightly-bound layer of polarized cells?

Answer 8

Epithelial cells

Question 9

Which tissue has a low density of cells?

Answer 9

Connective tissue

Question 10

How is skin built up?

Answer 10

It’s an organ that consists of 2 tissues - epithelium (dermis, epidermis etc.) and connective tissue (blood vessels, nerves, tissue specific structures and cells, extracellular matrix). Basal lamina between epi. and connective T.

Question 11

Name 3 cells hanging out in the connective tissue of skin

Answer 11

Tissue macrophage: immune cell that can react on foreign stuff
Fibroblast: produces extracellular matrix
Mast cell - reacts on foreign attack, a type of white blood cell

Question 12

Which 2 structural fibers are most common in skin?

Answer 12

Elastin and collagen fibers

Question 13

There are some glycans in the connective tissue and basal lamina of skin, which ones and what are their 2 main categories?

Answer 13

Ground substance (gel): consists of proteoglycans and hyaluronan
Matrix glycoproteins: fibronectin and laminin

Question 14

Describe the basic structure of collagen and what AA is most common

Answer 14

glycine is repeated every 3rd unit. 3 chains are assembled into a triple helix (tropocollagen) bound together by electrostatic bonds. Glycine is the smallest AA which make the chains come close together. The ends of the chain are unorganized.

Question 15

Briefly explain the collagen synthesis in the cell

Answer 15

Transcription - translation - synthesis of pro-alpha-chain - hydroxylation - glycosylation - self-assebmly into 3 pro-alpha-chains - formation of procollagen triple-helix - secretion - cleavage of propeptides into collagen - collagen fibril.

Question 16

What mechanical properties do collagen and elastin have?

Answer 16

Collagen is stiff and strong but still a bit elastic. Elastin is highly elastic, low modulus.

Question 17

Describe the ground substance

Answer 17

Consists of a hyaluronan backbone with attached proteoglycans which have a “bottle brush” morphology. The proteoglycan have a core protein with attached chains sugar molecules called glucoseaminoglycans (GAGs). The GAGs are negatively charged which repel each other and bind water - gel forming.

Question 18

Name some GAGs

Answer 18

Keratan-, chondroitin-, dermatan- and heparan sulphate. Hyaluranan is also included as well as heparin (most negatively charged molecule in the body)

Question 19

Why is the gel matrix so important?

Answer 19

It helps transferring signaling molecules and bind growth factors. The GFs can be docked on the GAGs which prevent enzymatic degradation and help present them to cell receptors.

Question 20

Describe the two matrix glycoproteins

Answer 20

They have multiple bioactive peptides acting as binding sites. They function as a glue between cells and ECM.

Question 21

What is fibronectin?

Answer 21

A glycoprotein. Have different functional peptides such as heparin binding sites, RGD sequences (cell receptor binding), collagen bind. site also self-association sites. Because of these bind. sites it works as a glue - makes it good to have on biomaterial surfaces!

Question 22

Describe laminin

Answer 22

Cross-shaped glycoprotein with 3 primary chain. Major component of the basal lamina influencing cell differentiation, migration, and adhesion.Can bind to cells by integrin receptors.

Question 23

What are integrins

Answer 23

Integrins are transmembrane receptors that facilitate cell-extracellular matrix (ECM) adhesion. Upon ligand binding, integrins activate signal transduction pathways that mediate cellular signals such as regulation of the cell cycle, organization of the intracellular cytoskeleton, and movement of new receptors to the cell membrane.

Question 24

Which two cellular intefaces are there in tissues?

Answer 24

Cell-Cell contact (tight junctions, desmosomes, gap junctions)
Cell-ECM contact (hemidesmosomes, focal adhesion)

Question 25

Describe the Cell-ECM interface

Answer 25

The cell membrane integrated integrin can bind to many different ECM proteins such as the glycoproteins to build an inter-connectivity between the ECM and the cells.

Question 26

How does the integrin receptor work?

Answer 26

Consists of a alpha and a beta, which makes it a heterodimer. They are bound togheter and one end is inside the cell (bind cytoskeleton) and one outside (bind ECM). It needs to have a stand up position to get activated. When activated (from the inside or outside) the two dimers loose contact/gets further apart.

Question 27

Describe focal adhesion

Answer 27

Clustering of integrin receptors that bind ECM proteins leading to the formation of focal adhesions. The focal adhesion complex works as a physical link between several integrins and actin cytoskeleton. They mediate regulatory signals and mechanical force between the ECM and cell.

Question 28

What is the difference between proteoglycans and glycoproteins?

Answer 28

Proteoglycans are proteins that are heavily glycosylated (core protein and long chain sugar molecules attached). Glycoproteins are also proteins, they have covalenty bound oligosaccharides to the peptide chain.

Question 29

What’s the importance of cell attachment?

Answer 29

Highly affect cell fate processes such as viability, protein synthesis, communication, proliferation, migration, activation/differentiation and apoptosis. Biomaterials need to support these functions.

Question 30

How does cells attach to biomaterial surfaces?

Answer 30

They attach to proteins absorbed at the biomaterial surface by the same mechanism that they attach to tissue ECM, that is through focal adhesion.

Question 31

Which one of glycoprotein or proteoglycan consists of the highest amount carbohydrates?

Answer 31

Proteoglycans with 50-60% while glycoproteins have 10-15%