Cell Ultrastructure And Molecular Building Blcks 2

Question 1

Nucleus

Answer 1

• Brain of the cell

• Double nuclear membrane

• Houses DNA (in the form of chromatin) within the nucleolus (site of ribosomal RNA formation i.e DNA transcription)

Question 2

Mitochondria

Answer 2

• Site of oxidative phosphorylation

• Double membrane, inner membrane is highly folded

• Outer membrane: Lipid synthesis & Fatty acid metabolism

• Inner membrane: Respiratory chain (electron transport) ATP production

• Matrix: Tricarboxylic acid (Krebs’) cycle

• Intramembranous space: Nucleotide phosphorylation (ADP to ATP)

Question 3

Rough endoplasmic reticulum

Answer 3

(rough due to numerous ribosomes on surface):

• Site of protein synthesis

• Highly folded flattened membrane sheets

Question 4

Smooth endoplasmic reticulum

Answer 4

• Site of membrane lipid synthesis

• Processes and stores synthesised proteins

• Highly folded flattened membrane sheets

Question 5

Golgi apparatus

Answer 5

• Parallel stacks of membrane - processes and modifies macromolecules synthesised in the endoplasmic reticulum

• Cis (first) golgi (nuclear facing - near nucleus) - receives SMOOTH ENDOPLASMIC RETICULUM vesicles, protein phosphorylation occurs here

• Medial golgi (in the middle, central part) - modifies products by adding sugars - forms complex oligosaccharides by adding sugars to lipids and peptides

• Trans golgi network (last, this transfers) - proteolysis of peptides into active forms and sorting of molecules into vesicles which bud from the surface

• Located close to the nucleus of the cell

• In most cells the golgi apparatus cannot be seen, HOWEVER it can be seen clearly in plasma cells [exam question]

Question 6

Vesicles

Answer 6

• Very small, spherical membrane-bound organelles which transport & store material and exchange cell membrane between compartments

• Many types: Cell-surface derived (pinocytotic and phagocytotic vesicles), golgi- derived transport vesicles, ER-derived transport vesicles, Lysosomes and Peroxisomes

Question 7

Lysosomes

Answer 7

(contains digestive enzymes) - Waste disposal system and is the site of breakdown for most molecules, derived from golgi, H+ - ATPase (pump H+ ions into cell) on membrane creates low pH (pH5) to enable acid hydrolases to function

They also breakdown debris from dead cells & bacteria and damaged cell organelles.

Question 8

Peroxisomes

Answer 8

small, membrane-bound organelles containing enzymes which oxidase long-chain fatty acids (long chain FAD-amino oxidase, catalase and urate oxidase - INVOLVED IN THE PROCESS BY WHICH FATTY ACIDS ARE BROKEN DOWN INTO TWO-CARBON FRAGMENTS WHICH THE CELL CAN USE AS A SOURCE FOR GENERATING ATP) - BETA OXIDATION.

They also produce hydrogen peroxide (by-product of the breakdown of fatty acids) which can be used to destroy pathogens etc. hydrogen peroxide is toxic to cells, but peroxisomes can destroy hydrogen peroxide thereby preventing its toxic effects and protecting the body etc.

Question 9

Cytoskeleton

Answer 9

Filamentous proteins which brace the internal structure of the cell - helps cells maintain their shape and internal organisation

• Not visible in light microscopy

Question 10

Microfilaments (5nm)

Answer 10

ACTIN forms a bracing mesh (cell cortex) on the inner surface of the cell membrane

Question 11

Intermediate filaments (10nm and 6 types of proteins)

Answer 11

Anchored transmembrane proteins which can spread tensile force through tissues. Specific functions unknown. 6 proteins:

• Cytokeratins - epithelial cells (found in many different cells)
• Desmin - myocytes
• Glial fibrillary acidic protein (supports neurones in the brain) - astrocytic glial cells
• Neurofilament protein - neurons
• Nuclear laminin - nuclei of all cells
• Vimentin - mesodermal cells

Question 12

Microtubules (25nm)

Answer 12

TUBULIN ( alpha and beta, which arrange in groups of 13 to form hollow tubes).

Arise from centrosome (comprises of 2 centrioles).

Found in all cells except for erythrocytes (red blood cells) - erythrocytes have no nuclei thus no microtubules required since no cell division occurs thus no cell structure is really required

Question 13

Storage products and inclusions

Answer 13

• Lipofuscin - Membrane-bound orange-brown pigment, peroxidations of lipids (degradation of lipids) in older cells, common in heart and liver, found in older people - sign of wear and tear

• Lipid - Non-membrane-bound vacuoles, appears as empty space in histology since dissolved in processing, stored in adipocytes and liver

• Glycogen - CHO polymer in cytoplasm, normally only seen on electron microscopy, may accumulate in some cells and in some diseases

Question 14

Molecular building blocks

Answer 14

• Basic building blocks are: Carbon, Hydrogen, Oxygen, Nitrogen, Sulfur & Phosphate (CHONSP)

Question 15

Macromolecules

Answer 15

• They are simple molecules such as sugars, lipids and amino acids and can form complex large molecules

• They can have osmotic, structural, optical, enzymatic and other complex functions

• Examples include; Haemoglobin, DNA, glycogen, rhodopsin and collagen

Question 16

Carbohydrates

Answer 16

• General formula; Cn(H20)n

• Examples; Monosaccharides, Disaccharides, Oligosaccharides & Polysaccharides

• Glucose + galactose = lactose
• Glucose + fructose = sucrose
• Glucose + glucose = maltose

Question 17

Monosaccharides

Answer 17

• Chain of carbons, hydroxyl groups, one Cketon carbonyl (C=O) group OOHC

• An aldose has an aldehyde (C1) OHC HC OH

• A ketose has a keton (mostly C2)

Question 18

D&L

Answer 18

Chiral centre is a carbon with 4

• D & L monosaccharides have the same chemical properties but different biological ones

• There will be two optically active and different forms

• Most sugars living in organisms are D, when not indicated its the D form

Question 19

Cyclized (ring) structures

Answer 19

By the reaction of the aldehyde or ketone groups with a hydroxyl group of the same molecule, monosaccharides generally exist as ring structures

Question 20

Glycosidic bond

Answer 20

The hydroxyl group of a monosaccharide can react with an OH or an NH group to form a glycosidic bond.

• O-glycosidic bonds (oxygen i.e hydroxyl) form disaccharides, oligosaccharides and polysaccharides

• N-glycosidic bonds (nitrogen i.e amine (NH)) are found in nucleotides and DNA

Question 21

Oligosaccharides

Answer 21

Disaccharides contain 2 monosaccharides (MS) joined by an O-glycosidic bond.

Oligosaccharides contain 3-12 MS.

Oligosaccharides are the product of digestion of polysaccharides, or part of complex protein/lipids.

Question 22

Polysaccharides-1

Answer 22

Formed by thousands of MS joined by glycosidic bonds e.g. Starch - storage in plants, made of amylose (glucose alpha 1,4) and amylopectin (glucose alpha 1,4 and alpha 1,6 glycosidic bonds)

• Proteoglycans - long, unbranched polysaccharides radiating from a core protein [found in animals]

Question 23

Polysaccharides-2

Answer 23

GLYCOGEN - storage in animals, is a branched polysaccharide formed of glucose residues.

Linkage is both alpha 1,4 (between carbons) and alpha 1,6 (between side chain and main chain) - branching is at regular intervals.

Core protein is glycogenic, amino linked to the only reducing end of the inner chain.

Question 24

Lipids: Triglyceride = 3 fatty acids bound to glycerol

Answer 24

• Straight carbon chains (mostly 16-20) with a methyl group (CH3) and a carboxyl group (C=OOH) at the ends. Melting point decreases with the degree of unsaturation (fluidity). Some of the C-C bonds can be unsaturated (i.e have double bonds). Tend to be hydrophobic and contain no oxygen in main chain.

• In unsaturated fatty acids, the double bonds are commonly cis and spaced at 3C intervals

Question 25

Nucleotides

Answer 25

building blocks of DNA.

Made from: nitrogenous base (Adenine-Guanine (two carbon-nitrogen rings - purines),Cytosine-Thymine (one carbon-nitrogen ring - pyrimidines) in DNA & A-U,C-G in RNA) + sugar (ribose (RNA) or deoxyribose (DNA))+ phosphate

Question 26

Bonds between nucleotides

Answer 26

Hydrogen bonds

A-T is 2 H bonds

G-C is 3 H bonds

Question 27

Phosphodiester bonds

Answer 27

Bonds between phosphate and sugar

Phosphate bonds in nucleotides are a source of energy

Question 28

Amino acids

Answer 28

Building blocks of proteins- 20 in total

Carbon with amino group, carboxyl group and side chain

Question 29

What is Charge of amino acid is determined by

Answer 29

Charge is determined by all three components. Charge changes somewhat with the ph of the solution

Side chain often determines polarity (hydrophilic) or non-polarity (hydrophobic) of the amino acid.

Question 30

Glutamic acid charge

Answer 30

net negative charge since 2 carboxyl groups and only 1 amino group.
• Carboxyl groups = negative
• Amino group = positive
Nitrogenous base + Sugar + Phosphate charged positively

Question 31

Most natural form of amino acids and sugars

Answer 31

Amino acids: L

Sugar: D

At different pH carboxyl and amino groups are ionised (charged)