COURSE CODE: BCH 222COURSE TITLE: Functional BiochemistryNUMBER OF UNITS:2 UnitsCOURSE DURATION: Two hours per week

COURSE LECTURER: Dr. UGBENYEN ANTHONY MOSES

INTENDED LEARNING OUTCOMES

At the completion of this course, students are expected to:

1. Define various concept of Signal transduction (e.g hormones and neurotransmitters).

2. List and classify plant and animal hormones.3. List the different classes of neurotransmitters.4. Draw the biochemical structure of the listed neurotransmitters.5. Understand how hormones and neurotransmitters transduce signal.6. Understand the concept of second messenger in signal transduction.7. Understand the role of cAMP, IP3, Ca2+ in sensing and processing stimuli.

COURSE DETAILS:

Week 1-2: Introduction to the concept of signal transduction. Hormones and neurotransmitters Week 3-4 Plant hormones (Auxins, gibberellins, cytokinin etc)Week 5-6: Animal hormones (Insulin, Parathyroid, estrogens and androgens)Week 7-8: Structures and function of different neurotransmittersWeek 9-11 Concept of second messenger in signal transduction.Week 12 Revision

RESOURCES

• Lecturer’s Office Hours:• Dr. Ugbenyen A. M. Mondays 12:30-2:30pm.• Mr. Ehiosun Kelvin, Wednesdays 2-4pm, • Course lecture Notes:• Books:

Lehninger, A. L., Nelson, D. L., & Cox, M. M. (2000). Lehninger principles of

biochemistry. New York: Worth Publishers.

Rodwell, V. W., Botham, K. M., Kennelly, P. J., Weil, P. A., & Bender, D. A. (2015).

Harper's illustrated biochemistry (30th ed.). New York, N.Y.: McGraw-Hill

Education LLC

Course Project:• Seminar presentation by student.• Assigment + written test: ~ 30% of final grade.• Exams:• Final, comprehensive (according to university schedule): ~ 70% of final gradeAssignments & Grading• Academic Honesty: All classwork should be done independently, unless explicitly stated otherwise on the assignment handout.• You may discuss general solution strategies, but must write up the solutions yourself.• If you discuss any problem with anyone else, you must write their name at the top of your assignment, labeling them “collaborators”.• NO LATE HOMEWORKS ACCEPTED• Turn in what you have at the time it’s due.• All homeworks are due at the start of class.• If you will be away, turn in the homework early.

PREAMBLE:

An introduction to biochemical information flow, strategies of signaling

(physical and chemical) presented in a hierarchical fashion. Hormones and

neurotransmitters as chemical mediators of signals in plant and animals. An

outline of the physiological action of auxins, gibberellins, cytokinins, insulin,

Parathyroid hormone, estrogens and androgens. Ligand-gated nerve of nerve

impulse (action potential, acetylcholine and other neurotransmitters e.g. GABA

serotonin, norepinephrine). Signal transduction cascades to highlight the roles

of cAMP, IP3. diacylglycerol and Ca2+ ions in sensing and processing stimuli.

Composition of muscle and biochemistry of muscle contraction.

FUNCTIONAL BIOCHEMISTRY by UGBENYEN M. ANTHONY is licensed under a Creative Commons Attribution- NonCommercial - ShareAlike 4.0 International License

CONCEPT OF SIGNAL TRANSDUCTION IN LIVING THINGS

The ability of cells to receive and act on signals from beyond the plasma membrane is

fundamental to life. Bacterial cells receive constant input from membrane proteins that act as

information receptors, sampling the surrounding medium for pH, osmotic strength, the

availability of food, oxygen, and light, and the presence of noxious chemicals, predators, or

competitors for food. These signals elicit appropriate responses, such as motion toward food

or away from toxic substances or the formation of dormant spores in a nutrient-depleted

medium.

In multicellular organisms, cells with different functions exchange a wide variety of signals.

Plant cells respond to growth hormones and to variations in sunlight. Animal cells exchange

information about the concentrations of ions and glucose in extracellular fluids, the

interdependent metabolic activities taking place in different tissues, and, in an embryo, the

correct placement of cells during development. In all these cases, the signal represents

information that is detected by specific receptors and converted to a cellular response, which

always involves a chemical process. This conversion of information into a chemical change,

signal transduction, is a universal property of living cells.

The number of different biological signals is large, as is the variety of biological responses to

these signals, but organisms use just a few evolutionarily conserved mechanisms to detect

extracellular signals and transduce them into intracellular changes.

MOLECULAR MECHANISMS OF SIGNAL TRANSDUCTION

Signal transductions are remarkably specific and exquisitely sensitive. Specificity is achieved

by precise molecular complementarity between the signal and receptor molecules (Fig. a),

mediated by the same kinds of weak (non-covalent) forces that mediate enzyme-substrate and

antigen-antibody interactions.

Multicellular organisms have an additional level of specificity, because the receptors for a

given signal, or the intracellular targets of a given signal pathway, are present only in certain

cell types. Thyrotropin-releasing hormone, for example, triggers responses in the cells of the

anterior pituitary but not in hepatocytes, which lack receptors always) in the ligand-receptor

interaction, and amplification of the signal by enzyme cascades.

The affinity between signal (ligand) and receptor can be expressed as the dissociation

constant Kd, usually 10-10

M or less—meaning that the receptor detects picomolar concentrations of a signal molecule.

Cooperativity in receptor-ligand interactions results in large changes in receptor activation

with small changes in ligand concentration. Amplification by enzyme cascades results when

an enzyme associated with a signal receptor is activated and, in turn, catalyzes the activation

of many molecules of a second enzyme, each of which activates

many molecules of a third enzyme, and so on (Fig. b). Such cascades can produce

amplifications of several orders of magnitude within milliseconds.

The sensitivity of receptor systems is subject to modification. When a signal is present

continuously, desensitization of the receptor system results (Fig. c); when the stimulus falls

below a certain threshold, the system again becomes sensitive. A final noteworthy feature of

signal-transducing systems is integration (Fig.d), the ability of the system to receive multiple

signals and produce a unified response appropriate to the needs of the cell or organism.

Plant Hormone

Introduction

The word hormone is derived from a Greek verb meaning “to excite.” Found in all

multicellular organisms, hormones are chemical signals that are produced in one part of the

body, transported to other parts, bind to specific receptors, and trigger responses in targets

cells and tissues. Only minute quantities of hormones are necessary to induce substantial

change in an organism. Often the response of a plant is governed by the interaction of two or

more hormones.

Thimann (1948) designated the plant hormones by ‘phytohormones’ in order to distinguish

them from animal hormones. He defined phytohormone as “an organic compound produced

naturally in higher plants, controlling growth or other physiological functions at a site

remote from its place of production and active in minute amounts.”

In general, plant hormones control plant growth and development by affecting the division,

elongation, and differentiation of cells. Some hormones also mediate shorter-term

physiological responses of plants to environmental stimuli. Each hormone has multiple

effects, depending on its site of action, its concentration, and the developmental stage of the

plant.

There are five (5) major plant hormones, namely;

• Auxins

• Cytokinins

• Ethylene

• Abscisic acid

• Gibberellins

1. AUXINS

Kögl and Haagen-Smit in1931 introduced the term ‘auxin’ (auxeinG = to grow or to increase)

for designating those plant hormones which are specially concerned with cell enlargement or

the growth of the shoots.

An auxin may, thus, be defined as “an organic substance which promotes growth (i.e.,

irreversible increase in growth) along the longitudinal axis when applied in low

concentrations to shoots of the plants freed as far as practicable from their own inherit growth

promoting substances. Auxins may, and generally do, have other properties but this one is

critical”.

Auxin is produced in shoot tips and developing seeds. Some known actions

• Establishment of polarity of root-shoot axis during embryogenesis

• Cell elongation

• Cell differentiation

• Apical dominance

• Lateral root formation and adventitious root formation

• Fruit formation

2. Gibberellin

A gibberellin (abbreviated as GA, for gibberellic acid) may be defined as a compound which

is active in gibberellin bioassays and possesses a gibbane ring skeleton. There are, however,

other compounds (like kaurene) which are active in some of the assays but do not possess a

gibbane ring. Such compounds have been called gibberellin-like rather than gibberellins.

About 29 gibberellins were previously isolated and their chemical structures known. These

have been named as gibberellin A1 (GA1), gibberellin A2 (GA2) and so on up to gibberellin

A29 (GA29). Although the gibberellins were originally isolated from a fungus, but now they

have been shown to be present in almost all the groups of plant kingdom including

angiosperms, gymnosperms, ferns, mosses and algae but are unknown in bacteria.

Gibberellin A3 has been usually shown to be biologically most active followed by GA1, GA4

and GA2 in descending order of their activity.

Biosynthesis of Gibberellin

Gibberellin is produced in young, developing shoots and seeds. Some known actions include;

• Cell division

• Cell elongation

• Stimulate seed germination

• Stimulate flowering

• Stimulate fruit development

3. ETHYLENE

Ethylene is involved in the induction of senescence. During senescence, the degradation of

leaf material is initiated. Proteins are degraded to amino acids, which, together with certain

ions (e.g., Mg2+), are withdrawn from the senescing leaves via the phloem for reutilization. In

perennial plants, these substances are stored in the stem or in the roots. In annual plants, they

are utilized to enhance the formation of seeds. Ethylene induces defense reactions after

infection by fungi or when plants are wounded by feeding animals.

Biosynthesis of Ethylene (Production of ethylene occurs in most tissues under stress, senescence, or ripening)

In addition to stimulating the abscission of fruit, ethylene has a general function in fruit

ripening. The ripening of fruit is to be regarded as a special form of senescence. The effect

of gaseous ethylene can be demonstrated by placing a ripe apple and a green tomato together

in a plastic bag; ethylene produced by the apple accelerates the ripening of the tomato.

Bananas are harvested green and transported halfway around the world under conditions that

suppress ethylene synthesis (low temperature, CO2 atmosphere). Before being sold, these

bananas are ripened by gassing them with ethylene. Also, tomatoes are often ripened only

prior to sale by exposure to ethylene.

4. Abscisic Acid (ABA)

ABA synthesis occurs in leaves and also in roots, where water shortage would have a direct

impact. ABA can be transported by the transpiration stream via the xylem vessels from the

roots to the leaves, where it induces closure of the stomata. Later it turned out that the

formation of the abscission layer for leaves and fruits are induced primarily by ethylene.

ABA is a product of isoprenoid metabolism. The synthesis of ABA proceeds in several steps

via oxidation of violaxanthin

Function of Abscisic Acid

ABA has a major function in maintaining the water balance of plants, since it induces with

nitric oxide (NO) the closure of the stomata during water shortage.

5. Cytokinins

Cytokinins are prenylated derivatives of adenine. In zeatin, which is the most common

cytokinin, the amino group of adenine is linked with the hydroxylated isoprene residue in the

trans-position. In other cytokinins, benzyl derivatives, sugars or sugar phosphates are

attached to the adenine.

ABA is one signal that causes guard cells to release solutes and thus release water, making them flaccid and closing

the stoma (pore) between them

Solutes (e.g. potassium and chloride ions) accumulate in guard cells causing water to accumulate in guard cells, making them turgid

Synthesis of zeatin, a cytokinin

Functions of Cytokinins

• Cytokinins enhance plant growth by stimulating cell division and increase the

sprouting of lateral buds.

• As cytokinins override apical dominance, they are antagonists of the auxin

• Cytokinins retard senescence and thus counteract the phytohormone ethylene

• The larvae of some butterflies (e.g., Stigmella, which invade beech trees) use this

principle for their nutrition. They excrete cytokinin with their saliva and thus prevent

senescence of the leaves on which they are feeding.

Mature (i.e., differentiated) plant cells normally stop dividing. But by adding cytokinin and

auxin, differentiated cells can be induced to initiate cell division again.