SDL: Introduction to cells

Question 1

What is the cell membrane?

Answer 1

• Plasma membrane, barrier allowing transport of chemicals between extracellular environment and interior of cells, organelles also bound by plasma membrane

Question 2

What is the basic structure of the cell membrane?

Answer 2

• Basic structure is lipid bilayers, mainly composed of lipids, in which proteins and associated carbohydrates may be found.
• Bilipid structure sometimes referred to as fluid mosaic model, refers to idea that individual phospholipids can move in relation to each other, forms a dynamic structure in which:
  
  • Lateral movement of molecules aids cell mobility
  • Membrane is semipermeable
  • Breaks and tears sealed quickly
  • Larger molecules such as proteins can become embedded

Question 3

Describe the lipid composition of the cell membrane

Answer 3

• Membrane lipids:
  
  • Phospholipids form the basic structure of the cell membrane. 4 types of phospholipid, relative abundance of each in the membrane upper and lower layers alters the properties of the membrane.
  • When in an aq environment, phospholipids orientate with their hydrophobic tails away from contact with the water. Phospholipids spontaneously form a lipid bilayer when in water.
  • Cholesterol- occurs within the membrane and acts to limit the movement of the phospholipids making the membrane more rigid.
  • Glycolipids- occur on outer surface of the membrane with their associated sugars. May be involved in intercellular communication

Question 4

Describe the types of proteins in the cell membrane

Answer 4

• Membrane proteins:
  
  • Types found in membrane depend on cell type, number of different membrane proteins split into groups depending on their functions:
  • Structural proteins:
    
    • Proteins that attach cytoskeletal filaments to cell membrane
    • Adhesion molecules which attach cells to extracellular matrix
  • Transport proteins, such as carrier, pump, and channel proteins
  • Receptors, for chemical signalling between cells
    
    • Receptor proteins are more likely to be glycoproteins (a protein with associated carbohydrate molecules).
  • Proteins with enzymatic activity
  • Proteins can be embedded in the membrane or associated with membrane surface.

Question 5

What is each centriole composed of?

Answer 5

• Nine sets of 3 microtubules

Question 6

Do centrioles occur singularly or in pairs?

Answer 6

• Centrioles occur in pairs, found in area of cell near nucleus called centrosome (cell centre).
• In a pair of centrioles, the individual centrioles are arranged perpendicular to each other.

Question 7

What is the function of centrioles?

Answer 7

• Centrioles have two roles:
  
  • Organises the micro tubular network within the cell
  • Organises the development of the microtubules in the cilia.

Question 8

Describe the rER

Answer 8

• Network of tubules, vesicles and flattened cistern continuous with the nuclear envelope
  - Protein synthesis in conjunction with ribosomes and modification of newly synthesised protein by glycosylation and structural changes

Question 9

Describe the sER

Answer 9

• An irregular network of tubes and vesicles continuous with the rough ER
  - Lipid biosynthesis, protein processing and intracellular transport by packaging of products into vesicles

Question 10

Describe ribosomes

Answer 10

• Consists of 2 subunits
  
  • Site of mRNA translation for protein synthesis. Occurs either in cytosol (cell protein synthesis) or attached to ER (membrane or secretion protein synthesis)

Question 11

What is the function of the golgi apparatus?

Answer 11

• Has 3 main roles
  
  • Modification of proteins by addition of sugars
  • Proteolysis, activation of peptides
  • Sorting and packaging of macromolecules into vesicles for transport within cell and for secretion

Question 12

What are microtubules?

Answer 12

• Are hollow fibres present in all cells except red blood cells, formed from two protein subunits, alpha and beta tubules, which join alternatively to form protofilament chains, which arrange into groups of 13 forming the microtubule.
• Microtubules constantly forming and informing with cells, grow out of centrosome, stabilised by associating with various proteins.

Question 13

What are the functions of microtubules?

Answer 13

• Have many functions including:
  
  • Intracellular transport
  • Present in cilia and flagella
  • Form cell cytoskeleton
  • Form filaments of the mitotic spindle
  • Form centrioles and basal bodies

Question 14

What are intermediate filaments?

Answer 14

Named as such due to being in size between microtubules and microfilaments, vary slightly according to which cell type they appear in. E.g. cells showing muscle differentiation contain design and epithelial cells all contain cytokeratin.

Question 15

What are microfilaments made of?

Answer 15

Composed of actin, smallest proteins of cytoskeleton

Question 16

What is the function of actin?

Answer 16

• Actin has various roles with cells and various isoforms of actin occur in various amounts in different cell types:
  
  • Majority of microfilaments occur just below the cell membrane, where they form a cross linked mesh which provides mechanical support to the cell membrane.
  • Actin molecules can form bundles which protrude the cell membrane to form microvilli.
  • In some cells actin interacts with myosin to generate motion

Question 17

What are microvilli?

Answer 17

Small finger like projections that can be found on the apical surface (this is a surface that faces the lumen which is the inner cavity of an organ) of most epithelial cells. The number and shape of microvilli correlates with the absorptive capacity of the cell. Function of microvilli is to increase SA of cell.

Question 18

What is the function of mitochondria?

Answer 18

Mitochondria provide energy to cells through oxidative phosphorylations, present in all cells bar red blood cells.

Question 19

How are mitochondria believed to have evolved?

Answer 19

• Their morphology varies with cell type
• Believed to have evolved in eukaryote cells as a result of symbiotic relationship (a close, prolonged association between two or more different biological species) with a mitochondrion-like prokaryote organism. In support of this theory, mitochondria have their own DNA and can synthesise protein.

Question 20

What are the functions of the nucleus?

Answer 20

• Contains cell DNA
• Site of RNA transcription

Question 21

Describe the nucleolus

Answer 21

Nucleolus is a compartment within the nucleus, it’s the site of transcription and processing of ribosomal RNAs (rRNAs) and their assembly into ribosomal subunits before export to cytoplasm. Varies is size depending on how metabolically active cell is

Question 22

How is cell DNA organised, and what colour does metaphase turn when stained with prop-idiom iodide?

Answer 22

• Cell DNA organised into chromosomes, linear molecules of DNA. During metaphase of cell cycle, chromosome fully consist and can be visualised on metaphase spreads for karyotype analysis.
• Metaphase spread stained with prop-idiom iodide (stains DNA red).

Question 23

What are tissues formed from?

Answer 23

• Tissues are formed from cells
• Some of these cells will be specialised to the particular tissue, others will be part of a general system, such as blood vessels.

Question 24

What are epithelia comprised of?

Answer 24

• Epithelia are comprised of sheets of epithelial cells, which cover the outside of the body, line many hollow organs of the body and can have secretory and absorptive functions. There are a few major types:
  
  • Squamous cells- forming squamous epithelium e.g. skin and the lining of some hollow organs. Squamous means flat and the epithelium can either be simple- made up of a single layer of cells- or be stratified- made up of many layers of squamous cells.
  • Squamous epithelium in pathology refers to stratified epithelium such as skin, pathologists do not call other epithelia squamous.

Question 25

What is squamous epithelium formed of?

Answer 25

• Squamous epithelium is formed of multiple layers of squamous cells on top of each other, joined together by specialised junctions called desmosomes.
• Upper part of some squamous epithelia made of squamous cells filled with large amount of keratin (intermediate filament type), makes the surface hard-wearing, this appearance is typical of skin. Squamous epithelium can also be found in some organ linings such as the oral cavity (mouth and pharynx), oesophagus, anal canal and vagina.

Question 26

What is the surface of the skin called, and what cells is it composed of?

Answer 26

Surface of skin called ‘epidermis’, it is a stratified squamous epithelium (i.e. made up of many layers of squamous cells).

Question 27

What is the underlying dermis made of?

Answer 27

Underlying dermis made of fibrous connective tissue. Dermis is very thick in this skin, which is taken from someone’s back.

Question 28

What is the function of the glandular epithelial cells?

Answer 28

Glandular epithelial cells adapted to synthesise, secrete and absorb various substances.

Question 29

What do some glandular cells form?

Answer 29

Some glandular cells form sheets and line hollow organs. E.G. the GI tract is lined by columnar mucus secreting cells, which lubricate the contents. Some hollow organs are lined by columnar cells with hair-like projections called cilia on their surfaces. For example, the respiratory tract is lined by ciliated cells which waft dust out of the airways and back up to the mouth.

Question 30

What do some glandular cells secrete?

Answer 30

Some glandular cells secrete hormones into blood stream, e.g. Islet cells in pancreas can secrete insulin. Some glandular cells make other substances such as the breast epithelium, which produces milk.

Question 31

What do some glandular cells absorb?

Answer 31

Some types of glandular cells absorb material for example in the large bowel the lining cells absorb water and salts from the bowel contents.

Question 32

What do transitional cells line?

Answer 32

Transitional cells line the whole urinary tract from the inside of the kidney, down the ureters, into the bladder and all but the last part of the urethra, which is lined by squamous epithelium.

Question 33

What are the properties of transition epithelial cells?

Answer 33

Similar to squamous epithelium but has additional properties of being able to stretch and recoil to accommodate variable volumes of urine, and is resistant to any adverse effects of urine.

Question 34

What does the most superficial layer of transitional epithelium consists of?

Answer 34

Most superficial layer of transitional epithelium consists of umbrella cells, which cover several of the underlying transitional cells.

Question 35

Describe apidocytes

Answer 35

Adipocytes (fat cells) store fat, which serves as an energy reserve and insulation, and are involved in peripheral synthesis of some hormones.

Question 36

What is adipose tissue?

Answer 36

Layer of fat immediately under skin, and fat around some internal organs such as kidneys.

Question 37

Describe fibroblasts

Answer 37

All organ systems, bar CNS, have fibroblasts. These cells have a specialised function to make collagen, the protein secreted out of the cell into the spaces between organs. It forms part of the extra-cellular matrix (material outside and around cells) and forms a flexible but tough tissue which helps to hold soft organs in place within the body. Tendons are an example of fibrous connective tissue which join muscles and bones.

Question 38

Describe the types of connective tissue

Answer 38

• Loose (areolar)- contains elastic fibres and collagen bundles imbedded in ground substance. Found in mucosa and submucosa of various organs and surrounding many blood vessels, nerves and muscles.
• Dense irregular- contains coarse, irregularly arranged thick bundles of collagen fibres.
• Dense regular- composed of regular parallel bundles of collagen fibres with rows of fibroblasts between.

Question 39

What is bone made of?

Answer 39

Bone made of osteoblasts (bone cells).

Question 40

What is bone laid down by and onto?

Answer 40

Bone is laid down by osteoblasts onto a preformed structure of cartilage or fibrous tissue by a process called ossification, other cells (osteoclasts) ‘remodel’ the bone in response to weight or other forces.

Question 41

What else is bone comprised of?

Answer 41

Bone comprised of a large amount of extra-cellular calcified connective tissue with mature bone cells (osteocytes), osteoblasts and osteoclasts in it.

Question 42

What are the 3 main types of muscle cells in the body?

Answer 42

• 3 main types of muscle cells in body:
  
  • Skeletal muscle- which makes up muscles as we know e.g. abs
  • Cardiac muscle- heart muscle
  • Smooth muscle

Question 43

What are the properties of skeletal + cardiac muscle?

Answer 43

Skeletal and cardiac muscle cells have ‘striations’ or stripes when examined microscopically, hence they are forms of ‘striated’ muscle. The striations are formed by organisation of actin and myosin fibres within muscle cells in a very rigid arrangement.

Question 44

Describe the properties of smooth muscle

Answer 44

Smooth muscle makes up wall of all muscular internal organs, except heart. Smooth muscle cells have fewer, less rigidly arranged actin and myosin fibres and are therefore not striated. Smooth muscle is found in the wall of the bowel, uterus, fallopian tubes, bladder, blood vessels and many other organs.

Question 45

What is cartilage made of?

Answer 45

Largely made up of extra-cellular material with a few cells called chondrocytes.

Question 46

What do chondrocytes do?

Answer 46

Chondrocytes synthesise and secrete extra-cellular matrix material (glycoaminoglycans) which make up cartilage.

Question 47

What is the function of carilage?

Answer 47

Cartilage forms a low friction cover for bones where joints form.

Question 48

What do joints have?

Answer 48

Joints have fibrous tissue holding bones together and make a space or cavity around the whole joint.

Question 49

What is lining the joint cavity?

Answer 49

Joint cavity has a lining of synovial cells, which make joint fluid to allow easy movement and cushion bones.

Question 50

What do chondroblasts form?

Answer 50

Chondroblasts form areas of cartilage by proliferation of the chondroblasts which lay down the cartilage matrix. Once cartilage laid down the chondroblasts become less active and are now termed chondrocytes.

Question 51

Describe the 3 types of cartilage

Answer 51

• Hyaline- Type II collagen. Created as a temporary skeleton for formation of bone, found in joints and lungs.
• Fibrocartilage- Type I and Type II collagen. Found in intervertebral discs and tendon attachment to bones.
• Elastic cartilage- Type II collagen and elastic fibres. Found in ear, epiglottis and larynx.

Question 52

What is the nervous system comprised of?

Answer 52

• Made up of brain, spinal cord and nerves.
• Has neurones (nerve cells) and supporting cells.

Question 53

What do the supporting cells of the nervous system contain?

Answer 53

Supporting cells contain fatty myelin which acts as insulation between nerve fibres so that nerve impulses can travel without interference.

Question 54

What happens when blood supply to the heart is obstructed?

Answer 54

When blood supply to muscle of heart is obstructed by fatty deposits of atheroma in walls of blood vessels, heart muscle cells die. This is myocardial infarction or heart attack.