biochemistry, cell structure and function

7/31/2019 Biochemistry, Cell Structure and Function

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Copyright Allen R. Andrew 2012

Biochemistry, Cell Structure and Function2.1 Cell Structure and Function

Objectivesi. Identify some basic properties of cells

ii. Identify the differences between features of prokaryotes and eukaryotesiii. Differentiate cellular components of prokaryotes

iv. Differentiate between plant and animal cellsv. Identify cellular components and their function in animal and plant cells

vi. Describe the animal tissues and organ system

Basic Properties Complex and highly organized - Similar organelles and processes. Information to build a cell is encoded in its gene. Cell reproduces by cell division - Content from a mother cell is distributed into two daughter

cells following duplication of genetic material within mother cell. Cellular activity is fuelled by chemical energy. Light energy trapped in plants carbohydrate via photosynthesis fuel activities of almost all

organisms. Cells perform enzyme-controlled chemical reactions - Cellular metabolism Cells perform mechanical activities - Transport of material Cells respond to stimuli - Most cells covered with receptors that interact with specific stimuli Cells are capable of self-regulation

Prokaryotes and Eukaryotes Cells are divided into

Prokaryotes Eukaryotes

Share similar basic structures1. A boundary that separates intracellular from extracellular2. Contain a set of genetic information3. A cell body containing cytoplasm and ribosomes

General feature of Prokaryotes 2 common features

lack of nucleus absence of membrane-bound organelle

DNA not enclosed by nuclear membrane Primitive, simple, small Examples are bacteria and cyanobacteria Eubacteria: live in water, soil or within other organism Archaebacteria: live in inhospitable environment (thermoacidophiles, halophiles)


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Cellular Components in Prokaryotes5 main cellular components

Cell wall Plasma membrane Cytoplasm DNA Ribosome

1. Cell Wall Rigid cell wall , made up of peptidoglycans Maintain cell shape, protect from injury Carbohydrate content of peptidoglycan antigenic property of cell wall Host organisms produce antibodies to neutralize antigens Gram negative bacteria possess outer covering consisting lipid bound to protein and carbohydrate Other structures: flagella and pili (pilus).


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2. Plasma Membrane Consist mainly of lipid and protein components(different ratio depending on types of bacteria) Invagination of plasma membrane(mesosome)helps respiration Some contain light absorbing pigments on plasma membrane for photosynthesis

3. Cytoplasm Appears grainy due to protein-synthesizing unit called ribosomes Also contains other factors: RNA, enzymes, glycogen, polyphosphates and DNA

4. DNA Single, circular naked DNA Located in nucleoid Also contain plasmids

Plasmid can replicate independently of the main DNA

5. Ribosomes Smaller 70S (rate of sedimentation )ribosomes occur as free particles in cytoplasm Ribosomes contain two subunits. In prokaryotes, these subunits are 50S (large) and 30S (small). (less when the subunits are bound

then when they are separated).


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General Features of Eukaryotes DNA can be found in the chromosomes which are surrounded by a membrane nuclear envelope Many organelles Examples are protoctists, fungi, animals and plants

Animal Cells Typical animal cells consists of:

Plasma membrane Nucleus Mitochondria Endoplasmic reticulum Ribosomes Golgi apparatus Secretory vesicles Cytoskeleton

1. Plasma Membrane Separate from external environment Provide mechanical strength

Provide shape Composed of lipids, proteins and carbohydrates Semi-permeable Functional peripheral and integral membrane proteins(transport, receptors, nerve conduction,

contraction) Model of biological membrane

Fluid mosaic model Proposed by Singer & Nicolson (1972)


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Plasma membrane is not static but a dynamic fluid system where globular proteins and othercomponents can move laterally and intermix freely.

Main features of Singers model. Most cell membrane thickness~7-8nm Phospholipid bilayer: oily, giving membranes flexibility and fluidity Membrane proteins form the mosaic part 2 types of membrane proteins: peripheral and integral Membrane carbohydrates: glycoprotein, glycolipids (receptors, cell-cell recognition) Contain cholesterol, interspersed among phospholipids (less fluid at higher temperature) Cell membranes are asymmetric

Main Functions of Membrane Forms boundary Gives shape, mechanical strength, protection Regulates and control in-and out-flow of materials Receptor site

Cell- cell recognition In nerve cell: insulation and transmission of impulse Linked with neighboring cell with junctions

2. Nucleus Largest organelle Contain hereditary information Consist of nuclear envelope-bound nucleoplasm, with network of chromatin fibres and histone

proteins Nuclear pores for protein movement, RNA and other molecules Nucleolus is spherical, visible only upon staining: synthesis rRNA


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3. Mitochondria Site for aerobic respiration Bounded by two membranes:

-Porous outer membrane permeable to most small molecules-Inner membraneInner membrane form cristae containing respiratory complexesInter membrane space contain enzymes of nucleotide metabolism

Matrix: gel like, consisting enzymes, ions, small organic molecules, cDNA

4. Endoplasmic Reticulum Extensive and inter-connected membrane system constituting more than half of the cell total

membrane Encloses an internal space: ER lumen or cisternae space 2 forms of ER

-RER (synthesis of membrane protein and secretory proteins )-SER (lipid synthesis and biotransformation )


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5. Ribosome Small cytoplasmic organelle Function in protein synthesis Two subunits, work as one during translation

6. Golgi Apparatus For sorting, packaging and distribution of several types of proteins , small molecules and new

membrane to internal and external compartment. Has two faces

-Cis : cisterna positioned close to ER-Trans : closest to cell plasma membrane

Budding off small vesicles from ER will fuse with cis Golgi membrane, then process from one

sac to another till reaching trans face for distribution. Secretory products (digestive enzymes and hormones) concentrated within secretory vesicles orgranules that bud off from trans face, followed by exocytosis.


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7. Secretory Vesicles Have two :

a) Lysosomesb) Peroxisomes

a) Lysosomes Spherical organelle bounded by single membrane Contain granules or aggregates of digestive enzymes Function in digestion of food , worn out cell components and extracellular molecules Leakage in arthritis, gout

b) Peroxisomes Small, spherical Containing oxidative enzymes Function in breakdown of toxic peroxide molecules i.e hydrogen peroxide esp important in

hepatocytes and renal cells In plants, peroxisomes in leaves important for photorespiration (formation of CO2) In germinating seeds, peroxisomes (glyoxysomes) involved in conversion of lipid to

carbohydrates

8. Cytoskeleton Intricate supportive network of proteinaceous fibres and filaments in cytoplasm

Maintain overall cell shapes Facilitate cellular movement Provide supporting structure for movements E.g. microtubules, microfilaments, intermediate fibres


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Plant Cell Cell wall Chloroplast Plastid Vacuoles


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1. Cell Wall Surrounded plant cell outside plasma membrane Generally made of insoluble cellulose fibres in a matrix of polysaccharide and protein Cell wall composition varies from cell to cell and species to species Adjacent plant cells fused together through middle lamella which is formed from calcium pectate

(pectin) Functions of cell wall

Provide form Support structure Protection from injury Physical barrier from pathogen invasion Osmotic entry of water in plants

Removal of cell wall results in protoplast which is vulnerable to changes in surrounding Exposure of protoplast cell burst

2. Plastid

Found only in plants, algae and some protists Bounded by double membrane Three types:

a) chromoplasts b) leucoplasts c) chloroplast

Involved in storage of substances such as starch or proteins, accumulated pigments responsiblefor the color of leaves, petals and fruits

a) Chromoplasts Does not contain chlorophyll Yellow, orange or red due to the presence of caratenoids pigments synthesized and stored in it.

Give color to young leave s, flowers and ripening fruits Can be formed from chloroplasts that have lost their chlorophyll and internal membrane( during

ripening of fruits)

b) Leucoplasts Storage plastids for nutrient such as starch, oil and protein granules Not colored Plastid full of starch: amyloplasts , found in root sand tubers such as potatoes, carrots Elaioplasts are leukoplasts that store oil Aleuroplasts are leukoplasts that store proteins Prolonged exposure to light, leukoplast can become chloroplast

c) Chloroplast A type of plastid Specialized for conversion of light energy into chemical energy Structurally similar to mitochondria The outer membrane is highly permeable Inner membrane relatively impermeable Inner membrane contains carrier protein to control molecules movement Contains chlorophyll molecules, bound to thylakoid membrane proteins


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Chlorophyll capture light energy during photosynthesis Portions of thylakoid membranes form tightly stacked structures : grana ( increase surface area

for attachment of chlorophyll) Space enclosed by thylakoid membrane: thylakoid lumen Surrounding thylakoid membrane: stroma Stroma contains enzymes, DNA, RNA and ribosomes

3. Vacuoles Fluid-filled sac surround by single membrane (tonoplast) Clearly seen within the cytoplasm Most mature plants have one large central vacuoles Store amino acid, sugars, ions and toxic waste Help cell growth Central vacuoles expand during growth process and fluid pressure builds up inside the cell,

forcing its flexible wall to enlarge Central vacuoles can increase and occupy 50- 90% of cells interior


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Animal Cell VS Plant Cell

Animal Cell VS Plant CellNO cellulose cell wall VS Have rigid cellulose cell wall

NO chloroplasts VS Chloroplasts present in photosynthetic plantsSmall, temporary vacuoles VS Large, permanent vacuoles

Centrioles present VS No centriolesCarbohydrate storage glycogen VS Carbohydrate storage starchSome cells have cilia or flagella VS No cilia or flagella

Lysosomes present VS Lysosomes usually absentSmaller than plant cells VS Often larger than animal cells

Specialised Animal Tissue and Organs Multicellular organisms perform different functions Cells becoming specialized during development Cells adapted and achieve particular structure suitable for their function i.e. size, shape, internal

structure and content Group of cells performing similar functions tissues which act as a unit Several types of tissue that work together to perform specific function is organ

1. Epithelial Tissue

I. Simple Epithelia Composed of closely aggregated cells arranged in flat sheets


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III. Glandular Epithelia Contain secretory cells Multicellular glands contains specialised secretory cells A cord of cells formed from the surface epithelium, and invaginate inward, resulting to :

i) Exocrine gland (salivary gland, digestive gland)ii) Endocrine gland (pituitary gland, thyroid gland)

2. Nerve Tissues Neurons Glial cells

I. Neurons/ Nerve CellsHighly specialized for conduction of nerve impulse3 common features:

1. A cell body that contain nucleus


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2. A number of short fibres, dendrites, extending from cell body, that receive messagesfrom other neurons and send messages towards cell body3. Axon, single long fibre which takes impulses away from cells

The tips of axon meet Other neurons at junction called synapse Muscles(neuromuscular junction) Glands

Three types of neurons: Motor neurons (efferent) Sensory neurons (afferent) Associative neurons (interneurones)

1. Motor neurons transmit impulses along the axon from nervous system to muscles and glands


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2. Sensory neurons (afferent) Conduct impulses from the receptor organ to the central nervous system

3. Associative neurons (interneurones/ intermediary/ relay neurons) Occurs within the central nervous system (CNS) or sympathetic ganglia Receive impulses from sensory neurons or other intermediary neurons Exist in various shapes with one or more dendrons or axons

II. Glial Cell Neuroglial cells/ Neuroglia

Provide support, protection and nourishment to the neurones Also functions to

Stimulate formation of new synapse Modulate the activity of neurons Repair damage Supply neurons with materials from blood


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-Types of neuroglial cells Schwann cells that produce myelin sheath which surrounds many axons in PNS Myelin sheath is separated at nodes of Ranvier, to facilitates faster movement of impulse

III. Muscles Tissues Muscle cells To produce motion 3 types: smooth , striated (skeletal) and cardiac muscle Form muscle fibres specialized for contraction

1. Smooth muscle cells (involuntary) Variable length Found in digestive tract, walls of trachea, uterus, bladder Contraction controlled by brain via autonomic nervous system Contracts rhythmically, producing waves of contraction such as peristalsis

2. Striated muscle (voluntary) Skeletal muscle Large number of muscle fibres Multinucleated (have more than one nucleus per cell) Each fibres has alternating dark and light bands Attached to bones via tendons


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Essential part of organ of support and motion

3. Cardiac muscle (involuntary) Only found in heart Cells have single nucleus and many mitochondria Also striated, but different from skeletal, because it is:

Mechanical contraction last longer Does not require impulse from brain Myogenic, has its own pacemaker


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1. Give body shape and provide framework for support (eg.skeleton)2. Protect the internal organs (eg.the cranium protects the brain, the ribcage protects the heart)3. Provide surfaces for attachment of skeletal muscles to enable movement4. Act as a reservoir for calcium and phosphorus5. Site for blood cell production in the bone marrow

Diseases related to bones Rickets (poorly calcified deformed bones) lack of calcium absorption from the intestines, due to

the deficiency of vitamin D Osteomalacia (bones do not calcify properly in adults) prolonged deficiency of vitamin D Osteoporosis decreasing bone mass

2. Cartilage A connective tissue containing cells embedded in a matrix of chondrin 3 types:

(i). Yellow elastic cartilage located in the pinna and epiglottis(ii). White fibrous cartilage in the ligamentous capsules surrounding joints and the

intervertebral discs(iii). Hyaline cartilage

Functions of hyaline cartilage:- Elastic compressible tissue located, such as cartilage of trachea and bronchi , to keep themopen- Covers the ends of bones and reduces friction between joints during movement- Forms the embryonic skeleton in many bony vertebrates- Forms the skeleton of cartilaginous fish such as sharks and stingrays

3. Blood cells 3 main types: Erythrocytes (red blood cells) Granulocytes & Agranulocytes(white blood cells) Platelets (thrombocytes)

Erithrocyte (red blood cell)- Lifespan 120 days- Diameter 7 8 m, 2m thick


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- Biconcave, disc-shaped, cell is covered by a thin, elastic plasma membrane- Functions:

(i) Contain haemoglobin, to transport oxygen and carbon dioxide(ii) Act as buffers and helps to maintain the pH of the blood

Granulocytes ( presence of granules) :1. Neutrophiles (70% of the leucocytes)

- Life span 6 hours to a few days- Diameter 10 15 m- Cytoplasm contains fine, non-staining granules- Functions:

(i) Engulf microorganisms (eg.bacteria) by phagocytosis , and destroy them2. Eosinophils (1.5% of the leucocytes)

- Lifespan - Several days- Diameter 10 15 m- Cytoplasm contains fairly large granules- Functions:

(i) To control allergic response3. Basophils (0.5% of the leucocytes)

- Lifespan - 1- 2 years- Diameter 14 - 16 m- Cytoplasm contains fewer but larger granules- Functions:

(i) Involved in inflammation and allergic reactions

Agranulocytes ( absence of granules):1. Lymphocytes (24% of the leucocytes)

- Life span several months to years- Diameter 9 16 m (smallest cells in the leucocytes)- Functions:

(i) For specific immune response

(ii) B-lymphocytes produce antibodies to destroy antigens(iii) T-lymphocytes attack and destroy infected cells

2. Monocytes (4% of the leucocytes)- Lifespan few days (blood), and several months (connective tissue)- Diameter 16 20 m (largest cell of the leucocytes)- Cytoplasm is non-granular- Functions:

(i) Engulf antigens, and destroy dead/ damaged cells of the body


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Platelets (thrombocytes)- Lifespan 8 12 days- Diameter about 3 m- Irregularly shaped membrane-bounded cell fragments- Functions:

(i) Important in the process of blood clotting

Functions

Transport Protective FunctionsHomeostasis

Leucocytes(neutrophils,macrophages) engulf antigens eg. bacteriaby phagocytosis

B-lymphocytesproduce antibodies todestroy pathogens /to neutralize toxins T-lymphocytes destroyinfected cells

Platelets, fibrinogenand prothrombininvolves in bloodclotting to reduceblood loss and entryof pathogens

Helps to regulate andstabilise the internalenvironment Water content of the

plasma helps toregulate bodytemperature

Solutes in the bloodsuch as plasma

proteins, mineral ions(eg. Na+) affect the

water potential of theblood and regulatediffusion of water

between blood andtissues

The hydrogencarbonate, some

plasma proteins andhaemoglobin act asblood buffers and

help to maintain thepH of the blood

HormonesInsulin

from pancreas to liver

Absorbed substancesGlucose, amino acids,

mineral ions,vitamins

from small intestines

Respiratory gases Oxygen, carbon dioxide

Excretory wastes Urea, creatinine, uric acid

to theexcretory organs

biochemistry, cell structure and function

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