Human Cell Biology and Physiology Timothy Billington Ph

Human Cell Biology and Physiology Timothy Billington Ph. D

I BLOCKED OUT YOUR VIEW OF THE SUPERMOON

Week 7 I trust that your steep learning JAY curve is as gentle as this one:

Week 7 beginneth Quick revision questions on ABO blood groups A Type AB person is transfused with Type O red cells. What is the result? A Type A person is transfused with Type O plasma. What do you predict? A Type B person receives a transfusion of Type A plasma. What happens?

CELLS of the DIGESTIVE SYSTEM A. Stomach B. Intestine A. Cells lining the Stomach Gastric glands G cells

Gastric Gland continues Mucosal cells Secrete mucous to protect the stomach lining from acids Parietal cells PA-RYE-ET-AL Secrete Hydrochloric acid (HCl) and Intrinsic Factor HCl kills micro-organisms ingested with food, denatures proteins and inactivates any enzymes in ingested food breaks down plant cell walls breaks down connective tissues in meat maintains a highly acidic environment ( much more acidic than lemon juice ) Intrinsic Factor helps absorb Vitamin B 12 across intestinal lining

Chief Cells Secrete PEPSIN, an enzyme which hydrolyses ingested food proteins G-Cells Secrete Gastrin stimulates secretions from Parietal and Chief Cells contractions of the stomach wall to aid churning and mixing You have heard of PEPTIC ULCERS perhaps?

B. Cells lining the Intestine Microvilli Villi increase Microvilli Villi 2 shown here surface area for absorption Villus is lined with villous cells Capillary network Lacteal vessels take away lipids M Each villous cell has microvilli which further expand the surface area enormously Villi line the small intestine

Inside surface of small intestine is lined with a ‘forest’ of villi Huge increase in surface area for absorption Each villus in turn is coated with cells ( enterocytes ) which have microvilli on their absorptive surface SINGLE enterocyte with its coating of microvilli

WHAT are the NUTRIENTS in INGESTED FOOD? 1. Complex carbohydrates: these are long chains of sugar molecules = polysaccharides 2. Lipids: these are fats, a. k. a. triglycerides 3. Proteins: these are long chains of amino acids = polypeptides

DIGESTIVE SYSTEM BREAKS DOWN FOOD MOLECULES TO: OBTAIN ENERGY

Energy Extraction from Foods 13

WHAT are the EVENTS in the BREAKDON and ABSORPTION of NUTRIENTS in FOOD? CARBOHYDRATES: Complex carbohydrates begin to be broken down by the enzyme AMYLASE in the saliva. Products are di-saccharides ( pairs of sugar molecules) and tri-saccharides (groups of 3 sugars in a chain) Microvilli membranes contain 2 enzymes (di-saccharidases and tri-saccharidases) which then break down di- and tri- saccharides into monosaccharides Monosaccharides enter the cytoplasm of the enterocyte and are then transported into the capillaries at the base of each enterocyte Capillaries eventually join the portal venous system which takes the monosaccharides to the liver for further metabolism

LIPIDS: Digestion begins in the mouth, via enzymes called lingual LIPASES Tri-glycerides are broken down to mono-glycerides and fatty acids Monoglycerides and fatty acids then enter the microvilli by diffusion They form complexes with proteins. Complexes are called chylomicrons Chylomicrons are actively taken up into the capillaries, thence to the liver.

PROTEINS: PEPSIN ( a hydrolase) hydrolyses proteins into smaller chains of amino acids called polypeptides Enzymes Trypsin and Carboxypeptidase hydrolyse polypeptides into shorter peptides and eventually into single amino acids via the enzyme Dipeptidase which is in the microvilli membranes themselves amino acid 1 - amino acid 2 (= di-peptide) amino acid 1 + amino acid 2 dipeptidase single amino acids Amino acids then diffuse into the capillaries, thence to the liver via the portal vein.

Only the side chain ( R group ) differs between the amino acids

NEW TOPIC: CELLS of the LIVER Ga Gall Bladder Common Bile Duct Location of Liver

LIVER CELLS a. k. a. HEPATOCYTES Sinusoid Hepatocyte Kupffer Cell Hepatocyte Hepatic Artery Portal Vein LIVER LOBULE Bile Duct 1/6 th OF A LOBULE Enlarged Details

LIVER carries out essential metabolic and synthetic functions regulates metabolism, regulates haematological content blood supply to the liver 1/3 is arterial blood [ hepatic artery ] 2/3 is venous [ hepatic portal vein ( from intestinal capillary circulation)] bile duct from gall bladder, supplies bile to emulsify fats blood drains from the liver hepatic vein empties into the vena cava, thence to heart, thence to lung

FUNCTIONS SUMMARY OF LIVER CELLS: Metabolic Regulation by Hepatocytes 1. Carbohydrates (glucose) maintains glucose level in circulating blood. Hepatocytes can store excess glucose as glycogen 2. Lipids regulates blood levels of triglycerides, fatty acids and cholesterol 3. Amino Acids Hepatocytes remove xs amino acids from the blood Questions: Which enzyme-controlled process produced the amino acids? Where did the glucose come from?

Metabolic Regulation by Hepatocytes continues: 4. Wastes removal Convert ammonia to urea and delivered it to the blood to be excreted by the kidneys. Inactivate therapeutic and other drugs and blood-borne toxins. 5. Vitamin storage Vitamins A, B 12, D, E and K are extracted from the blood stream and stored until needed by the body. When your diet contains inadequate amounts of these vitamins, they can be released by the liver. 6. Iron storage Excess Fe is combined with a protein and stored as Ferritin.

Haematological Regulation by the liver: 1. Antigen Presentation and Endocytosis 2. Synthesis of Plasma proteins Kupffer cells, lining the sinusoids, present Antigens to B-Cells which then manufacture Antibodies. K cells also endocytose cell debris including aged red cells Normal plasma proteins are synthesised by hepatocytes and delivered to the blood.

Haematological Regulation by the liver: 3. Removal of Antibodies Circulating Ab are hydrolysed to amino acids 4. Removal of Hormones Adrenalin and other hormones are absorbed and recycled by hepatocytes 5. Synthesis of Bile is synthesised by hepatocytes and stored in the Gall bladder Questions: What does Bile do? Antibodies are composed exclusively of …………. ?

25 NEW TOPIC - SYNTHESIS OF PROTEIN BY HUMAN CELLS

HOW DO CELLS SYNTHESISE PROTEIN? General scheme for synthesis: DNA m-RNA transcription Amino Acid chain = Protein translation DNA-dependent RNA polymerase

LET’S DERIVE an m-RNA SEQUENCE FROM a DNA SEQUENCE HERE is the DNA sequence

28 DNA sequence: GATCTTTCGAAAA Start deriving the m-RNA sequence Rule: T is replaced by U [uracil] There are no Thymines in RNA

29 We have the first DNA triplet GAT What would be the complementary RNA triplet?

Later on in that DNA sequence, there is aa AAA triplet What do you predict will be the complementary RNA triplet?

WHAT IS MESSENGER RNA ( m- RNA) ? Template strand of DNA HELICASE enzyme is unwinding the DNA double helix m-RNA strand being transcribed from DNA

WHAT IS TRANSFER RNA? Specific amino acid attached here Anti-codon

ON FUTURE SLIDES aa THAT t-RNA STRUCTURE WILL BE REPLACED BY AUG

Let’s now look at a sequence of amino acid additions to the growing chain m-RNA triplets (codons) are read on the ribosome t-RNA’s approach and bind their triplet anticodons to the m-RNA triplet codons Peptide bonds form between successive amino acids

m-RNA TRIPLET CODON interacts with t-RNA TRIPLET ANTICODON aa 1 UAC AUG GGU GUA CCC UGU ACG AAA GGA messenger RNA strand

m-RNA TRIPLET CODON interacts with t-RNA TRIPLET ANTICODON aa 1 aa 2 UAC CCA AUG GGU GUA CCC UGU ACG AAA GGA messenger RNA strand

m-RNA TRIPLET CODON interacts with t-RNA TRIPLET ANTICODON aa 1 Peptide bond is formed b/w aa 1 and aa 2 First t-RNA, minus its aa 1, leaves the m -RNA UAC Next t-RNA comes in and binds anticodon to the next m-RNA codon AUG GGU GUA CCC UGU ACG AAA GGA CCA CAU messenger RNA strand

WHAT is a PEPTIDE BOND? RESULT OF A DEHYDRATION SYNTHESIS BETWEEN the COO group on one amino acid and the NH 2 group on another amino acid R R

m-RNA TRIPLET CODON interacts with t-RNA TRIPLET ANTICODON aa 1 UAC Next t-RNA comes in and binds its anticodon to the next m-RNA codon. aa 2 CCA CAU AUG GGU GUA CCC UGU ACG AAA GGA messenger RNA strand

m-RNA TRIPLET CODON interacts with t-RNA TRIPLET ANTICODON aa 1 aa 2 aa 3 Peptide bond forms b/w aa 2 and aa 3. t-RNA minus its aa 2 leaves the m-RNA CAU AUG GGU GUA CCC UGU ACG AAA GGA messenger RNA strand

And so-on, until a STOP m-RNA triplet codon is reached by the triplet reading frame on the ribosome. Protein synthesis is then terminated. m-RNA strand is then degraded and its components recycled t-RNA molecules minus their amino acid moieties then combine with their specific amino acids from the cytoplasm. There is always an xs of t-RNA molecules in the cytoplasm There is always an xs of all 4 nucleotides in the cytoplasm There is always an xs of all 20 types of amino acids in the cytoplasm