Exam 3 Review

Base-Excesion DNA Repair

1) DNA Glycosylase recognizes a damaged base and cleaves between the base and sugar. 2) Endonuclease cleaves the phosphodiester backbone near the mutation site. 3) DNA Polymerase I fixes using the 5'→3' Exonuclease activity. 4) Ligated

PCR Steps

1) DNA strands are separated by heating 2) Strands are annealed to excess of primers 3) New DNA is synthesized by TaqI polymerase (thermostable)

Formation of Ribosome in Bacteria

1) IF-3 and IF-1 bind to the 30S subunit, which guides it to the Shine-Dalgarno sequence. 2) IF-2 brings in a GTP and a tRNA brings in a fMet into the P site. 3) The 50S subunit comes, hydrolyzes the GTP, and the IF's are released

Methyl-Directed Mismatch Repair

1) MutH binds to hemimethylated GATC. 2) MutL forms a complex with MutS at the mismatch. 3) DNA is threaded through the MutL-MutS complex until it encounters a MutH. 4) MutH cleaves the unmethylated strand. 5) DNA Polymerase III fills in the gap and the nick is sealed by DNA Ligase.

Collagen Synthesis

1) Preprocollagen is made bound to the ER 2) Removal of the signal peptide makes procollagen 3) Pro and Lys are hyrdoxylated using ascorbate 4) O- and N-linked glycosylation 5) Disulfide isomerase forms intra- and inter-chain disulfide bonds in the C-terminal domains 6) After being released, N- and C-terminal proteases cut the ends to form tropocollagen 7) Lysyl oxidase deaminates the amino group of some Lys and hydro-Lys to form aldehydes for crosslinks through aldol condensation or schiff base formation.

Components of a DNA E. coli Expression Vector

1) Promotor and operator 2) Termination Sequence 3) Selectable genetic marker 4) Ori 5) Gene encounter repressor that binds O and regulates P

Homologous Recombination Steps

1) Sequences with essentially the same sequence line up. 2) An endonuclease introduce single-strand nicks in both strands. 3) The strand exchange is mediated by rec A. Then the nicks are sealed by a DNA ligase. Sometimes, the branch point may shift through branch point migration. 4) If the branch point rotates, it forms a Holliday structure, which is resolved by an endonuclease

Methods of Proofreading Amino Acid tRNA Synthesis

1) Steric fit between amino acids and amino-acid-binding pocket 2) The aminoacyladenylate is hydrolyzed if the it does not match with the tRNA 3) When being released, the aminoacyl-tRNA is checed to see if it is a proper match. A mismatch is hydrolyzed.

Elongation of Peptide Chains in Bacteria

1) The next aminoacyl-tRNA binds to the elongation factor Tu, which also contains a GTP 2) The complex binds to the A site and the GTP is hydrolyzed. 3) The Tu-GDP is released. The Tu exchanges the GDP with Ts and Ts is exchanged with a GTP 4) The aminoacyl-tRNA's amino acid attacks the growing chain in the P site 5) The old tRNA is kicked out through the E site and the new one now occupies the P site. This translocation event is catalyzed by elongation factor G.

Ending of Translation in Bacteria

1) The release factor comes in to bind in the A site 2) Water is used to hydrolyze the link between the peptide chain and tRNA 3) Ribosome Recycling Factor (RRF), IF-3, and EF-G-mediated GTP hydrolysis causes it all to fall apart.

Breakdown of the Human Genome

30% Genes (1.5% exons and 28.5% interons and non-coding) 45% Transposons (21% LINEs and 13% SINEs) 25% Miscellaneous (3% short repeating sequences, 5% long repeating sequences) 8% Retrovirus-like

5' Cap of mRNA

7-Methylguanosine is added to the 5' end through a 5',5'-triphosphate linkage. GTP donates the guanosine; adoMet donates the methyl group.

Secondary Structure of tRNA

A cloverleaf structure of length 73 to 93 nucleotides. It has an arm with an amino acid arm A C C Pu, TψC arm, anticodon, and D arm with 2-3 dihydrouridine residues.

Palindrome Sequence to Form Hairpins

A sequence that is ordered like 4-3-2-1-1'-2'-3'-4' (where the prime is the compliment). This is not to be confused with a mirror repeat (4-3-2-1-1-2-3-4).

One-Color Quantitative Microarray Technology

A target is biotin-labeled cRNA (complimentary to cDNA). The probe is a single-stranded DNA oligo attached to a wafer. The duplix is stained with the streptavidin-bound fluorescent marker. It is used for finding which genes are in an individual, which genes make up proteins, and mutational analysis.

APH (NEO) and TK Genes

APH gives resistance to G418 and TK makes cells susceptible to Gancyclovir. When removing a gene to an animal, one clones the gene, sticks APH in the middle, and adds TK at the end. The cells that are resistant to G418 and Gancyclovir are the ones with the disrupted gene.

Inflamation and Adipocytes in Obese Individuals

Adipose tissue mass expands and adipocyte size increases. Adipocytes grow and secrete inflammatory cytokines. Those are what contribute to type II diabetes. In obese individuals, they contain 40% macrophages vs 5% in lean individuals. These adipocytes also breakdown TAG's into FFA's, which cause ER stress.

Polyol Pathway

Aldol reductase converts glucose to sorbitol using NADPH. It has a high Km, so it only occurs at high glucose levels. Sorbitol is converted to fructose using polyol dehydrogenase, which uses NAD+ (creates risk ROS from mitochondria usage).

DNA Polymerases in E. coli

All have a 3'→5' exonuclease I: Clean up during replication, repair, and recombination. Only one with a 5'→3' exonuclease. II: Repair III: Replication

Vitamin E and ROS

Ascorbate can be converted to dehydroascorbyl radical and then dehydroascorbate. It can then be reduced back using dehydroascorbate reductase. Two radicals can also dismutate into ascorbate and dehydroascorbate.

Base Pairings Recognized by Anticodon

Base pairings are allowed that do not decrease the distance between bases. U: A, G C: G A: U G: U, C I: U, C, A

TFIID vs SAGA

Both bind TBP, the molecular saddle that binds to DNA to initiate transcription, when facilitated by a mediator. TFIID is involved largely with housekeeping and is poorly regulated. SAGA is involved with stress and is highly regulated.

On and Off Ganglion Cells

Both ganglion cells continuously fire at a steady state. When on absorbs light, it speeds up its firing of Glu. When off absorbs light, it slows down its firing of Glu.

Marfan Syndrome

Caused by a mutation of fibrillin of elastin molecules. Can be seen with tall stature, long arms and legs, and arachnodactyly. It also leads to loose joints, deformed spine, mitral prolapse, and lens dislocation.

Formation of ACh

Choline acetyltransferase→ ACh

Elastin Structure

Composed of an elastin core and fibrillar layer of fibrillin. They contain little hydroxyproline and no hydroxylysine or carbohydrate chains unlike collagens. It also has no regular secondary structure.

Superoxide Dismutase and Catalase

Converts 2 superoxide oxygen radicals → ground-state oxygen and hydrogen peroxide. Then 2 hydrogen peroxide → water and oxygen

Proline Hydroxylase

Converts proline to hydroxyproline converting 2-oxoglutarate to succinate. It uses oxygen and Fe2+ and converts it to Fe3+ and CO2. To make this enzyme work again, ascorbate (vitamin C) must be converted to dehydroascorbate.

Energy Sources for Parts of the Eye

Cornea: 30% glycolysis, 60% pentose shunt. NADPH is used mostly by glutathione reductase to detoxify ROS (UV radiation) Lens: 85% glycolysis, 10% pentose shunt, and 3% TCA cycle Retina: 90% glycolysis

Sanger Sequencing

DNA is replicated many times, then it is heated. In addition to regular nucleotides, radio-labeled dideoxynucleotides are added too (cannot be extended afterwards). It is run on a capillary gel and ran through a laser beam.

Diagnosing Diabetes

Fasting Plasma Glucose: If it is over 7 mmol/L, there is diabetes. Below 6.1 mmol/L is normal. Oral Glucose Tolerance Test: If plasma glucose levels don't go under 10 mmol/L after a few hours, the patient is diabetic.

Formation of ROS

Fenton Reaction: Fe2+ and hydrogen peroxide → Fe3+, hydroxyl radical, and hydroxide anion Haber-Weiss: Superoxide and hydrogen peroxide → Ground state oxygen, hydroxyl radical, and hydroxide anion Metal-catalyzed Haber-Weiss: Superoxide and Fe3+ → oxygen and Fe2+, Fe2+ and hydrogen peroxide → Fe2+, hydroxyl radical, and hydroxide anion

Effects of High Ghrelin and Low Leptin

Ghrelin activates the NPY / AgRP neuron which causes the expression on NPY and AgRP. Both of which cause hunger. The lack of leptin causes a lowering in production of α-MSH, which normally binds to a melanocortin receptor. AgRP blocks the binding of α-MSH to this receptor.

Formation of GABA

Glu decarboxylase→ GABA

Glucagon Cascade

Glucagon binds to a g-protein receptor. That receptor activates adenylyl cyclase to send out cAMP. cAMP activates PKA, which indirectly activates phosphorylase through phosphorylase kinase and inhibitor-1. That inactivates glycogen synthase.

Glutamate NMDA Receptor

Glutamate binds to open a non-selective cation channel, which is more permeable to Ca2+ than Na+. It has binding sites for Glu, Gly, Mg2+, Zn2+, polyamines, and an antagonist binding site for PCP. Glu and Gly are required for activation. At negative membrane potentials, Mg2+ cause less current to flow through. It is both ligand-gated and voltage-gated.

Glutathione and ROS

Glutathione peroxidase reduces hydrogen peroxide and lipid peroxides using glutathione. Glutatione is recycled by glutathione reductase using NADPH

Different Types of ROS

Ground state oxygen e-→ superoxide oxygen radical (H+→ hydroperoxyl radical) e-→ hydrogen peroxide e-→ hydroxyl radical and hydroxide anion

Formation of Histamine

His decarboxylase→ histamine

Protein Motifs

Homeodomain: Helix-turn-helix type. They have a major groove protruding out that interacts with DNA. Leucine Zippers: Have two helicies wrapped around each other. The DNA binding part has Lys and Arg (+ charge) and the outside has evenly spaced Leu. Helix-loop-helix: Similar to leucine zipper, but only one pair of Leu residues. Zinc Fingers: Common for steroid receptors. It has three fingers. There are Cys and His that hold down a Zn.

Aggrecan Structure

Hyaluronic acid backbone → link protein → core protein → chains of sugar (chondritin sulfate, keratan sulfate, etc)

Lack of Insulin Symptoms

Hyperglycemia, osomtic diuresis leading to dehydration, increased lipolysis, ketonemia leading to acidosis and compensatory hyperventilation. The three main symptoms are polyphagia (hunger), polydispia (thirst), and polyuria (frequent urination).

Splicing of Group I vs Group II Interons

I: 3' OH of guanosine nucleophilically attacks the phosphate at the 5' splice spot. The 3' OH of the 5' exon becomes a nucleophile to get the downstream part of the exon off. II: 2' OH of adenosine in the interon attacks the 5' splice site to form a lariat structure. The 3' OH of the 5' exon becomes a nucleophile to get the downstream part of the exon off.

Type I vs Type II Diabetes

I: Autoimmune destruction of β-cells. Onset bellow 20 years old. Plasma insulin concentration is low or absent and there is are islet-cell antibodies. Obesity is uncommon and ketoacidosis is present. II: Insulin resistance or β-cell failure. Onset over 40 years old. Insulin concentration can be any level, there are no islet-cell antibodies, obesity is common, and ketoacidosis is uncommon.

Topoisomerases

IA: Breaks one strand and changes the linking number by increments of one IB: Breaks one strand and changes the linking number by more than one II: Breaks both strands and changes the linking number by increments of two

snRNPs

In metazoan nuclei. Splicing of most introns is directed by catalytic particles called spliceosomes composed of small nuclear RNAs (snRNAs) and proteins. These small ribonucleoprotein particles are called snRNPs ("snurps"). The catalytic steps are similar to those of Groups II introns with formation of a lariat intermediate and the free 5' exon.

Transcription Initiation and Elongation in E. coli

Initial interaction of the polymerase and promotor leads to a closed complex. σ binds from -10 to +2 or +3 TATA sequence. It opens up a transcription bubble. Once DNA transcription begins, it falls off. As it moves forward, the DNA is positively supercoiled ahead of the bubble and negatively supercoiled behind.

Insulin Cascade

Insulin binds to its receptor that has tyrosine kinase activity. It phosphorylates itself and insulin receptor substrates (IRS). Those activate things like PI3K. PI3K creates PIP3, which eventually activates PKC and PKB. Both of these activate GLUT4, which is known as an insulin-dependent glucose transporter. The Ser and Thr kinases lower in the cascade represent feedback inhibition.

cAMP Receptor Protein (CRP)

It binds to the lac operon in the absence of glucose. It positively regulates the lac operon.

Collagen Fibrils Structure

It consists of triple helices in a quarter-staggered alignment. They are stabilized by non-covalent forces and interchain crosslinks from Lys. It can be a mixture of different types of collagens, but type I is the most common.

Lac Operon Genes

It has a I, P, Z, Y, and A sections. They incode an inhibitor, promotor, β-galactosidase, galactoside permease, and thiogalactoside transacetylase.

α1-Antitrypsin

It inhibits the activity of elastase, which is a protease released by neutrophils. This molecule is therefore important in prevention of local tissue injury, especially in alveolar walls.

Collagen Structure

It is a right-handed triple helix consisting of three left-handed helices. The left-handed helix is more extended than a normal α-helix, as it twice the rise and only 3 (rather than 3.6) amino acids per turn.

Telomerase Activity

It is active in germinal and stem cells. It adds the sequence GGGTTA to nucleotides. After it alls off, it forms a GGGT hairpin. Each replication removes one telomeric unit.

Recombination of the V and J Gene Segments of Human IgG Kappa Light Chain

It is an example of site-specific recombination. 1) There are 1 to ~300 V segments and 5 J segments before a C sequence. 2) Recombination results in a loss of V and J segments. 3) Transcription. 4) Removal of sequences between the J and C through mRNA splicing. 5) Translation.

Construction of a cDNA Library

It is different from tissue to tissue and only is expressed protein. It is made using an mRNA template, which is annealed to a synthetic T primer (binds to poly A tail). Then a reverse transcriptase makes it longer. mRNA is degraded with alkali. The second strand is made with a separate primer.

Short Tandem Repeats

It occurs when two or more nucleotides are repeated. PCR is used with these. Then, they are run on a capillary tube and scanned to see the size of these.

Different Kinds of Cones

L: Long, yellow, 564-580 nm M: Medium, green, 534-545 nm S: Short, violet, 420-440 nm

Effects of Low Ghrelin and High Leptin

Leptin activates a POMC neuron which causes the expression of α-MSH. MSH binds to a melanocortin receptor, which inhibits food intake. Also, without Ghrelin, NPY and AgRP expression goes down, which also ceases hunger.

Rhodopsin Signaling to the Optic Nerve

Light hits rhodopsin, which causes it to activate the g-protein transducin. Transducin activates PDE, which breaks down cGMP. That cGMP was keeping open an Na+/Ca2+ symporter, which was depolarizing the cell. Once it is closed, it stops the release of Glu. Rhodopsin stops working when phosphorylated by Thr/Ser receptor kinase or with arrestin.

Effects of Glucocorticoids

Liver: + Glycogen storage, + gluconeogenesis Adipocytes: - glucose uptake and glycolysis, + lipolysis Muscle: + Protein degradation, - protein synthesis, - glucose uptake, - glycolysis (some say +)

Effects of Adrenaline

Liver: + Glycogenolysis, + gluconeogenesis from Ala, lactate, and glycerol Adipocytes: + Lipolysis Muscle: + Glycogenolysis, + glycolysis Pancreas: + Glucagon release, - insulin release Kidney: + Gluconeogenesis from lactate and Glu

Growth Hormone Effects

Liver: + Production and release of IGF-1, + glycogen storage, + gluconeogenesis (anti-insulin), - glycolysis (anti-insulin) Adipocytes: - Glucose uptake, - glycolysis, + lipolysis (all anti-insulin) Muscle: + protein synthesis, + nucleic acid synthesis, - glucose uptake (anti-insulin), - glycolysis (anti-insulin) Other: + chondrogenesis, + muscle growth, + visceral growth

Thyroid Hormone Effects

Liver: + glycolysis, + cholesterol synthesis, + triacylglycerol synthesis, + epinephrine sensitivity (+ gluconeogenesis, + glycogenolysis) Adipocytes: + glycolysis, + epinephrine sensitivity (+ lipolysis) Muscle: + glucose uptake, + protein synthesis, + epinephrine sensitivity (+ gluconeogenesis, + glycogenolysis) Calorigenic: + muscle cell permeability to Na+ → + hydrolysis of ATP because of Na/K pump + SNS release of norepinephrine → + uncoupling protein

Glycoxalase System

Methylglyoxal (MGO) is a reactive dicarbonyl sugar. It is formed during metabolism of Gly and Thr and nonenzymatic oxidation of carbohydrates and lipids. Glycoxalase I then II turns it into lactate.

Leptin Effects

Muscle and Liver: + AMPK, + free fatty acid oxidation, - lipogenesis CNS: - AMPK, - food intake (note that AMPK increases food intake)

Adiponectin Effects

Muscle: + AMPK, + glucose utilization, + free fatty acid oxidation Liver: + AMPK, - glucogenesis, + free fatty acid oxidation + Factors that counteract inflammatory cytokines

Formation of Vanillylmandelic Acid

Norepinephrine after the enzymes catecholamine-o-methyl transferase and monoamine oxidase work.

Phosphotidylinositol Signaling Cycle

PI is phosphorylated by PI4K then PI5K to make PIP2. It can then be phosphorylated by PI3K to make PIP3 or lysed by phospholipase c to make a DAG and IP3.

Glucagon and Gluconeogensis

PKA deactivates phosphofructokinase-2 and activates 2,6 bisphosphatase-2 that decreases the concentration of fructose 2,6 bisphosphate. This activates gluconeogenesis and decreasing glycolysis.

Glucagon and Fatty Acid Metabolism

PKA phosphorylates acetyl-CoA carboxylase, which turns it off to inhibit fatty acid synthesis. It also activates carnitine palmitoyl transferase I (CPT I) and decreases sensitivity to malonyl-CoA inhibition for fatty acid breakdown.

ROS Damage of Membranes

PUFAs can be susceptible a ROS plucking a proton making them a radical. Then a dienyl radical forms. Oxygen comes in to form of peroxyl radical. This radical can turn into a lipid peroxide by taking a proton from a different PUFA. Eventually these break down into malondialdehyde and a hydroxynonenal. The cycle can be broken by vitamin E.

ANS Transmitters

Preganglionic: ACh to nicotinic receptors (ionotrophic) Postganglionic Sympathetic: Norepinephrine Postganglionic Parasympathetic: ACh to muscarinic receptors (metabotropic)

ρ-Independent Termination of Transcription in E. coli

RNA polymerase may pause on some DNA sequences. It can keep going or the complex can undergo an isomerization. Then the RNA can form a hairpin to terminate transcription.

Methemoglobin Reductase

Reduces ferro(Fe3+)-methHb to ferro(Fe2+)-Hb after oxidative damage

Osteolathyrism

Result of lysyl oxidase inhibition oftentimes from β-aminopropiontrile (sweet pea). Symptoms include deformation of the spine, dislocation of joints, demineralization of bones, aortic aneurysms, and joint hemorrhages.

ρ-Dependent Termination of Transcription in E. coli

Rho is ATP dependent. It binds on a single-stranded region rich in C and poor in G upstream of the actual termination sequence. It then goes up the RNA until it hits the RNA-DNA region where it unwinds.

B-DNA Dimensions

Rise Between Bases: 3.4 Å Height of Turn: 36 Å Bases Per Turn: 10.5

Calcium Homeostasis

Serum concentration is maintained at 2.2-2.6 mmol/L. A decrease stimulates PTH to cause reabsorption from the kidney, bone, and gut (using vitamin d). An increase causes calcitonin release from the thyroid gland to inhibit kidney reabsorbtion and osteoclast bone resorption. Both hormones decrease phosphate concentrations.

Non-Homologous Recombination (Transposons)

Short Inverted Repeats at Each End: Encode a transposase, which moves the DNA Directly Repeated Long Terminal Repeats at Each End: Encodes a reverse transcriptase and resembles a retrovirus. It moves through an RNA intermediate. It has its own promoter. PolyA at 3' End of RNA Transcript with a Truncated 5' End: Encodes a reverse transcriptase. It moves through an RNA intermediate produced from a neighboring promoter.

Origin of Genetic Code Theories

Stereochemical: Origin of the genetic code is the physico-chemical interactions between codons and amino acids Co-Evolution: Initially, only a few amino acids that did not depend on other ones were encoded. As precursors gave rise to new ones, codon sets went through subdivisions.

Ectopic Fat Deposits

Systemic: Intra-muscular fat, fatty liver, visceral adipose tissue, which all cause metabolic risk. Local: Perivascular fat, pericardial fat, myocardial steatosis, renal sinus fat, which all cause vascular disease

Synthesis of Thyroid Hormone

TSH binds to its receptor. This causes the production of thyroglobulin and the opening of the I-, Na+ symporter. The thyroglobulin then enters the colloid. The I- is anti-ported out by Pendrin bringing Cl- in. The I- is converted to I+ using a peroxide by thyroid peroxidase. It binds to thyroglobulin, which re-enters the follicular cell and enters the lysosome where it is lysed. Then T3 and T4 are pumped out of the cell to bind to Zn finger receptors.

Priming tRNA

The amino acid is bound to an AMP by hydrolysis of ATP. Then the 5'-aminoacyl adenlyate (aminoacyl-AMP) can bind to the tRNA at either the 2' or 3' of adenine (eventually will go to 3').

Supercoiling

The mathematical property that represents the change in the sum of twist and writhe. Adding twists (counterclockwise) is positive supercoiling and the opposite is negative. A plectoneme or toroid could form.

Cone and Rod Anatomy

There are detached free floating discs inside the rods, but they remain attached to the outer segment in cones. The opsin part has 7 helices modified with sugars and lipids. Opsin is found in cone, rod, and ganglion cells.

Excess Glucose in Plasma Effects

There is an increase in ROS. Glucose attaches to proteins forming schiff bases . They then undergo an amadori rearrangement, where one of the products is glycated hemoglobin. Further change leads to advanced glycation end products (AGE), such as 3-deoxyglucosone, glyoxal, and methylglyoxal. AGE binds to receptors on endothelial cells to stimulate proinflammatory pathways and expression of inflammatory cutokines.

Initiation of Transcription in Eukaryotes

There is an interaction between the TATA-binding protein (TBP) and the promotor. This recruits TIIF with Pol II. Finally, TFIIH comes in, which has helicase activity. The carboxyl-terminal domain of the largest Pol II subunit is phosphorylated by TFIIH, which allows the polymerase to escape the promotor and start transcribing.

Laminin Structure and Function

They are noncollagenous glycoproteins found in basement membranes. Their polymers are connected to type IV collagen through nidogen or entactin.

Proteoglycan Structure and Function

They form a gel in the ECM to give it rigidity. They contain large amounts of carbohydrates.Their sugar chains are very long unbranched that contain repeating disaccharide units with uronic acid and an amino sugar in their N-acetylated or sulfated forms. They are attached to proteins by Gal-Gal-Xyl

Linking Number

Total number of base pairs divided by the number of base pairs per helical turn. Example: 63 base pairs in the B form (10.5 bases per turn) has a linking number of 6.

Integrins Function

Transmit physical and/or mechanical signals from the ECM to the cell interior by initiating enzymatic cascades that lead to gene expressions. They are important in cell differentiation.

Formation of 5-Hydroxytryptamine

Trp hydroxylase→ 5-hydroxytryptophan decarboxylase→ 5-hydroxytryptamine

Formation of Epinephrine

Tyr hydroxylase→ DOPA decarboxylase→ dopamine hydroxylase→ norepinephrine methyl-transferase→ epinephrine

Hydrolysis of RNA

Under alkaline conditions, the 2' hydroxyl can nucleophilically attack the phosphodiester bond to make a cyclic monophosphate derivative. RNase can also hydrolize. Dicer cleaves double-stranded RNA to protect from viruses.

Lac Operon During Different Levels of Glucose and Lactose

When lactose is low, the repressor binds. When lactose is high, the repressor dissociates. When glucose is high, CRP is not bound (limiting transcription). When glucose is low, CRP binds.

Formation of ROS is Mitochondria

When semiquinone radical is formed as an intermediate in the reduction of Q by complex I, II, or III, oxygen can come and oxidize. This is especially problematic in ischemia reperfusion injuries.

Lysyl Oxidase

While building elastin, this converts lysine to allysine. This can react with other allysines or unmodified lysines to form pyridinium crosslinks. The overall structure of the result can be a cyclic desmosine or isodesmosine.

Retinol Cycle

β-Carotene enters the diet dioxygenase→ all-trans-retinal reductase→ all-trans-retinol isomerase→ cis-retinol DH→ cis-retinal. Cis-retinal is transported and then added to opsin by forming a schiff base rhodopsin. When light hits, rhodospin converts to metarhodopsin then splits to opsin and all-trans-retinal, which is transported to the pigment epithelial cells by intermediate rhetinal binding protein.

Bacterial RNA Polymerase

σ: Directs the polymerase to a specific promoter and determines the genes to be expressed. 70 is the most common for housekeeping and has the lowest Km. 54 does modulation of nitrogen levels and 28 does movement / eating. β: Catalytic subunit α: Assembly and binding of the upstream promotor elements