02. Chemical and Cellular Basis of Life Flashcards
How many elements occur naturally on the earth’s crust?
92 elements occur naturally on the earth’s crust.
How many elements are essential to continue a healthy life and reproduction?
20-25% of elements are essential for a healthy life and reproduction.
What elements make up most of living matter?
Elements C, H, O, N make up 96% of living matter.
What elements make up 4% of the mass of an organism?
Ca, P, K, and S make up most of the remaining 4% of the mass of an organism.
What elements make up 96.3% of a human’s body mass?
C H O N
What elements make up the remaining 3.7% of a human’s body mass?
Elements - Ca, P, K, S, Na, Cl, Mg
Trace Elements - B, Co, Cu, Cr, F, I, Fe, Mo, Mn, Se, Si, Sn, V, Zn
Why chemical properties of water makes it important for life?
- It is a vital chemical constituent of the living cell
- It provides a biological medium for all organisms
Write 3 physical properties of water
Being a small, polar, and angular molecule
How do the properties of water arise?
The properties of water arise due to attractions of different water molecules. When water is in its liquid form H bonds are very fragile and the H bonds form, break and reform with great frequency.
Write the 4 major properties of water to maintain life related to functions
(CAVES)
1. Cohesive behavior
- Ability to moderate temperature
- Versatility as a solvent
- Expansion upon freezing
Write an example for cohesive behavior
Due to cohesion between water molecules, water and dissolved substances such as minerals and nutrients transport through vascular tissues, xylem and phloem against gravity.
Water has a high surface tension. This ability is given to water molecules, due to cohesion between the water molecules. In an aquatic system, upper surface water molecules are attracted by lower surface molecules and it forms a water film.
Small insects ( e.g. water skaters ) can walk on the surface of a pond.
Write an example for adhesive behavior
Adhesion between water molecules and cell walls also helps in conduction of water and dissolved substances
Write an example for water’s ability to moderate temperature
Evaporation of sweat from human skin helps to maintain the body temperature at constant level.
Transpiration in plants keeps the plant body surface as a cool surface and prevent from becoming too warm in the sunlight.
Due to the high specific heat, water will function as thermal buffer in living system and aquatic bodies during the temperature fluctuations on earth.
Due to the high heat of vaporization, with the minimum loss of water an organism can release much heat energy. Therefore, body surface of an organism maintained as cool surface.
e.g. Prevent from overheating.
Write an example for water’s property of expansion upon freezing
ice floats on the surface of water bodies. It is an important property of water in polar regions, where, organisms in aquatic bodies can survive during the winter.
Write an example for water’s property of versatility as a solvent
Polar molecules (e.g. Glucose), non-polar ionic (e.g. NaCl), both polar and ionic (e.g. lysozymes) can dissolve in water
Name the simplest formula of carbohydrate
(CH20)n
Name the simplest formula of carbohydrate
(CH20)n
According to number of carbons, name the types of carbohydrates
3C- Triose
4C- Tetroses
5C- Pentoses
6C- Hexoses
Name examples for triose
Glyceraldehydes (Phosphoglyceraldehyde is a derivative of
Triose)
Name an example tetrose
Erythrose (rare in nature)
Name an example for pentose
Ribose
Deoxyribose
Ribulose (RUBP is a derivative of ribulose)
Name an example for hexoses
Glucose
Fructose
Galactose
Name types of carbons according to their carbonyl groups
Aldoses-glucose, galactose
Ketoses-fructose
Name an example for aldoses
glucose
galactose
Name an example ketoses
fructose
Name features of polysaccharides
*macromolecules
*biopolymers
*Polysaccharides are made up of few hundred to a few thousand monosaccharide subunits
*They are non crystalline, water insoluble, and not considered as sugar
Name the types of polysaccharides based on their functions with examples
Storage- Starch, Glycogen
Structural- Cellulose, Hemicellulose, Pectin
Name the type of polysaccharide based on their architecture
Linear forms- Cellulose, Amylose
Branched forms- Glycogen, Amylopectin, Hemicellulose
Name the monomer and the function of starch
Glucose
stored in plants
What is the monomer of glycogen and its function
Glucose
stored in animals and fungi
What is the monomer of cellulose and its function
Glucose
Cellulose in the cell walls of plants and chlorophytes
What is the monomer of inulin and its function
Fructose
stored in the dhalia tubers
What is the monomer of pectin and its function?
Glactouronic acid
Component of middle lamellae of the plant cell wall
What is the monomer and the function of Hemicellulose?
Pentose
Component of the plant cell wall
What is the monomer and the function of Hemicellulose?
Pectin
Component of the plant cell wall
What is the monomer of Chitin?
Glucosamine
Component of the fungal cell wall and the exoskeleton of the arthropods
What is the nitrogen containing polymer?
Chitin
Name the functions of monosaccharaides
Energy source
Building blocks of disaccharides and polysaccharides (disaccharides such as maltose, sucrose and polysaccharides such as starch, glycogen)
Components of nucleotides (DNA, RNA)
Name the functions of monosaccharaides
Energy source
Building blocks of disaccharides and polysaccharides (disaccharides such as maltose, sucrose and polysaccharides such as starch, glycogen)
Components of nucleotides (DNA, RNA)
What are the functions of disaccharides
Storage sugar in milk- Lactose
• Translocation in phloem –Sucrose
• Storage sugar in sugarcane- Sucrose
What are the properties of lipids?
Diverse group of hydrophobic molecules
Large biological molecules but not considered as polymers or macromolecules.
Consist of C, H, O and H:O ratio is not 2:1. Comparatively more H are present.
Biologically important types of lipids: Fats, Phospholipids and Steroids.
How is triacylglycerol molecule is formed?
Fatty acid molecules bind to each hydroxyl group of glycerol by ester bond. Resulting
fat molecules are called as triacylglycerol.
Name an example for saturated fatty acids
butter
Name an example for unsaturated fatty acid
vegetable oils. Unsaturated fats may classify based on the nature of their double bonds.
a) Cis Unsaturated fat
b) Trans Unsaturated fat
What leads to atherosclerosis?
Consumption of excess saturated fats and trans unsaturated fats contribute arthrosclerosis.
What are phospholipid molecules made out of?
two fatty acids
one phosphate group attached to one glycerol molecule.
What does the phosphate molecule give the phospholipid molecule?
gives the additional negative electrical charge to the molecule
What is linked to the phosphate group of the phospholipid molecule?
an
additional polar molecule or small charged molecule is also linked to the phosphate
group e.g. choline.
How does the phospholipid molecule show different behaviour?
The two ends of the phospholipids show different behavior.
The hydrocarbon tails are
hydrophobic while phosphate group
its attachment (head) are hydrophilic.
What are the functions of lipids?
Food reserve as energy source (triglycerides such as fats and oils)
maintain the fluidity of plasma membrane (phospholipids, cholesterol)
act as signaling molecules (eg. Hormones) that travel through the body
• found as components of animal cell membrane (cholesterol)
What are the monomers of proteins?
Amino acids
Name the elemental composition of proteins
C, H,O,N and S
What is the amino acid molecule composed of?
amino group
a carboxyl group
a hydrogen atom
a variable group symbolized by R, which is an alkyl group.
What part of amino acid differs with each amino acid?
group also called the ‘side chain’ differs with each amino acid where as the other groups are in the ‘ back bone
What part of amino acid differs with each amino acid?
group also called the ‘side chain’ differs with each amino acid where as the other groups are in the ‘ back bone
What are amphoteric amino acids?
When both characteristics are found in one molecule they are known as amphoteric molecules.
How does a peptide bond form?
Two Amino acids undergo condensation reaction by removing a water molecule from both and result a bond known as peptide bond
Give an example for secondary proteins
Alpha helix- e.g.Keratin.
β pleated sheet e.g.spider’s silk fi ber
Give an example for tertiary structure of proteins
most of the enzymes, myoglobin, albumin
Give an example for quaternary structure of protein
Hemoglobin
Collagen
What are interactions occurring between side chain/ R group of tertiary proteins?
H bonds
Disulphide bonds
Ionic bonds
Van der Waals interactions/ Hydrophobic interactions
What are the interactions occurring in the secondary structure of protein?
Intra molecular hydrogen bonds between the oxygen atoms and the hydrogen atoms attached to the nitrogen atoms, of the same poly peptide chain backbone,
What are the type of bonds seen in tertiary structure of proteins’ side chain?
teractions between the side chain/ R-group of amino acids;
• H bonds
• Disulphide bonds
• Ionic bonds
• Van der Waals interactions/ Hydrophobic interactions
What type of interactions occur in the quaternary structures of proteins?
By inter and intra-molecular interactions.
What are the factors affecting denaturation?
1.High temperature and high energy radiation
- Strong acids, alkaline and high concentrations of salts
- Heavy metals
- Organic solvents and detergents
What are the types of proteins present according to their functions?
- Catalytic proteins
2.Structural proteins - Storage proteins
- Transport proteins
- Hormones
- Contractile/ motor proteins
- Defense proteins
Give an example and a function of catalytic protein
Pepsin, Amylase
Catalyze the biochemical reaction.
Name an example and functions of structural proteins
Keratin - Prevent desiccation
Collagen - Provide strength and support
Name an example and a function of storage proteins
Ovalbumin Storage protein in egg
Casein- Storage protein in milk
Name an example and the function of transport proteins
Hemoglobin - Transport O2 and CO2
serum albumin - Transport of fatty fats
Name an example of hormone and a function of the hormone
Insulin - Regulate blood glucose level
Glucagon
Name an example and a function of contractile/ motor protein
Actin and Myosin proteins - contraction of muscle fibers
Name an example of defense protein and its function
Immunoglobins- Eliminate foreign bodies
Name the monomer of nucleic acids
nucleotides
What are the elemental composition of nucleic acids?
C,H,O,N,P
What are the two types of nucleic acids?
- DNA
2.RNA
What the three components of nucleic acids
- pentose sugar
- Nitrogenase base
3.Phosphate group
What is a nucleotide without a phosphate group
Nucleoside
(Adenosine, Guanosine)
What are the two types of nitrogenous bases according to the size?
- purines (larger)
2.pyrimidines (smaller)
What is the difference between purines and pyrimidine?
- Purines- larger in size with two rings
- Pyrimidines- smaller in size with a single ring
what are the functions of DNA?
Store and transmit genetic information from one generation to the next generation
• Store the genetic information for protein synthesis
What are the three types of RNA
- Messenger RNA (mRNA)
- Transfer RNA (tRNA)
- Ribosomal RNA (rRNA)
What are the functions of mRNA (least abundant)?
• Copies the genetic information stored in DNA molecule as a sequence of
nitrogenous bases
• Transports genetic information from nucleoplasam to the site of protein synthesis
(ribosome) through nucleopores
What is the function of tRNA?(Linear, but forms three- looped structure)
transportation of amino acids to the site of protein synthesis.
Explain the structure of R-RNA?
It is the most abundant type of RNA.
rRNA has a complex irregular structure.
It provides the site where polypeptide chains are assembled
What is the function of RRNA
It provides the site where polypeptide chains are assembled
What are the differences between DNA and RNA?
- DNA is double stranded molecule while RNA is a single stranded molecule.
- DNA consists of A, T, G and C and absence of U, while RNA consists of A,U, G and C and absence of T
- Sugar molecule in RNA is ribose, while in DNA it is deoxyribose.
What are Nucleotides other than those found in nucleic acids?
ATP, NAD+, NADP+, FAD
What are Nucleotides other than those found in nucleic acids?
ATP, NAD+, NADP+, FAD
What is the function of ATP?
Universal energy carrier
What is the Functions of NAD+?
• Act as a coenzyme
• Act as an electron carrier
• Function as an oxidizing agent during respiration
What is the function of NADP+?
• Act as coenzymes
• Act as an electron carrier
• NADP+ act as a reducing agent in photosynthesis
What is the function of FAD?
• Act as a coenzyme
• Act as an electron carrier
What nucleotides act as coenzymes?
NAD+
NADP+
FAD
What nucleotides act as electron carriers?
NAD+
NADP+
FAD
What are the two types of microscopes?
- Transmission electron microscopes (TEM)
- Scanning electron microscopes(SEM)
What is the weakness of the light microscope?
The limitation imposed upon the resolution power of the light microscope by the
wavelength of light. The resolution power is inversely proportional to the wavelength.
Due to this, scientists considered the use of other forms of radiations with comparatively
shorter wavelengths.
As a result, electron microscopes were developed. In electron microscopy, a beam of
electrons is focused through the specimen or on to its surface.
What is the difference between TEM and SEM?
TEM: It is used to study the internal structures of cells.
In this microscope, a beam of electrons is passed through a thin, especially prepared slice of material.
A very thin specimen is used. Specimens stained with heavy metals which attach more to certain cellular
structures than other areas.
SEM: In this instrument, a fine beam of electrons is reflected from the surface of specimen.
Specimen is mostly coated with gold prior to observation.
Here the specimen scatters many electrons whereas others are absorbed.
This instrument is ideal to observe the
surface view in three dimensional appearances.
What is the difference between light and electron microscope?
Light Microscope
Glass lenses are used to focus the light rays
Actual color of the object can be observed
Living and non living objects can be observed
Dyes used to stain the object
Image is directly detected by naked eye
Electron microscope
Powerful magnets are used to focus beam of electrons
Not directrly detected by naked eye, micrographs are used
Actual color cannot be observed.
Images are developed
Heavy metals are used to stain the object
Robert Hooke
examined a cork using simple microscope and gave the term
“CELL” to describe the basic units.
Anton Van Leeuwenhook
a contemporary of Robert Hooke, was the first to describe and record living single celled organisms, Euglena & bacteria
Matthias Schleiden
a botanist, studying plant tissues concluded that all plants are made up of cells.
Theodore Schwann
a zoologist concluded that animal tissues are also made up of cells.
Rudolf Virchow
showed that all cells arise from pre-existing cells by cell division,
Schleiden, Schwann and Virchow presented the ‘Cell Theory’ which includes?
1.All organisms are composed of one or more cells.
2.The basic structural and functional unit of organisms is the cell.
3.All cells arise from pre-existing cells.
All cells share certain basic features. They are;
• All cells are bounded by a plasma membrane which is a selective barrier
• Within the cell have, a semifluid, jelly like substance which is called cytosol. Subcellular components are suspended within the cytosol.
• They carry DNA as genetic materials.
• Ribosomes are found in all cells
What are examples for prokaryotes and eukaryotes
Bacteria, Cyanobacteria and Achaea are prokaryotic cells. All the other organisms
have eukaryotic cells.
What are the features of eukaryotes?
Eukaryotes: DNA is linear and contained in a nucleus. DNA is associated with proteins
& Both 70s (Mitochondria and Chloroplast) and 80s ribosomes (larger) present (may attach to endoplasmic reticulum)
Mitosis, meiosis, or both;
1.8 billion years ago ,evolved from prokaryotes
Mainly multicellular (except most of protista and some fungi are unicellular)
Protists, Fungi, plants, animals are examples of this
10µm-100µm diameter is the cell size.
None have the ability to undergo Nitrogen fixation
Mitochondria for aerobic respiration
Chloroplasts containing membranes which are usually stacked into lamellae or grana
Flagella: Complex, with ‘9+2’ arrangement of microtubules; intracellular (surrounded by cell surface membrane) 200nm diameter
Cell walls: Cell walls of green plants and fungi are rigid and contain polysaccharides; cellulose in plant cell walls and chitin in fungal walls (none in animal cells)
Organelles: Many organelles, membrane bounded organelles present. Great diversity of organelles.
e.g. nucleus, mitochondria, chloroplasts
bounded by two membranes.
e.g. Lysosomes, Vacuole, bounded by
single membrane
What are the features of prokaryotes?
Bacteria, Archaebacteria
Average diameter 1-5µm
Mainly unicellular
3.5 billion years ago originated
Binary fission, no mitosis and meiosis
DNA is circular and lies free in the cytoplasm. This region is called nucleoid, DNA is naked
and not associated with proteins
70s ribosome (smaller)
No chloroplasts; takes place on membranes which show no stacking
Some have the ability of N2 fixation
Respiration: Mostly by mesosomes
Flagella: Simple, lacking microtubules; extracellular (not enclosed by cell surface membrane) 20nm diameter
Cell walls: Peptidoglycan present in Bacteria and cyanobacteria, polysaccharide and protein present in
Archae bacteria
Organelles: Few organelles, none are surrounded by membrane Internal membranes scarces; if present usually associated
with respiration, photosynthesis and N2 fixation
What is the plasma membrane composed of?
• Phospholipids (most abundant type of lipid in plasma membrane)
• Protein
What are the functions of the plasma membrane?
• The plasma membrane surrounds the cytoplasm of living cell physically
separating the intracellular components from the extracellular environment.
• Plasma membrane is selectively permeable and able to regulate the exchange of
material needed for survival.
• Proteins embedded in the plasma membrane identify the cell, enabling nearby
cells to communicate with each other (involved in cell recognition).
• Some protein molecules act as receptor molecules for interacting with specific
biochemical, such as hormones, neurotransmitters and immune proteins.
• Some proteins in the cell membrane attach to some cytoskeletal fibers and help to maintain the shape of the cell.
• Some proteins in the membrane act as enzymes. (e.g. Microvillus on epithelial
cell lining of some parts of the gut contains digestive enzymes in their cell
surface membrane.)
What are the functions of the nucleus?
• Control all cellular activities.
• Synthesize DNA to produce new nuclei for cell divisions.
• Synthesize rRNAs and ribosomal subunits required for protein synthesis, through
nucleolus.
• Synthesize mRNA and tRNA according to the information present on the DNA.
• Store and transport genetic information.
What are the two types of ribosomes?
70s
80s
Where can we find ribosomes?
70S ribosomes are found freely on the cytoplasm of prokaryotes, matrix of mitochondria and stroma of chloroplasts.
80S ribosomes are found only in eukaryotes.
What is the function of ribosomes?
Protein synthesis
What is the function of RER?
• Transport protein synthesized by ribosomes
• Synthesizing glycoproteins
• Produce transport vesicles
• Facilitate the growth of own membrane by adding phospholipids proteins and
carbohydrates. Therefore called as membrane factory
function of SER….
• It synthesizes lipids including oils, steroids and phospholipids.
• Metabolism of carbohydrates.
• Produce transport vesicles to transport within cell.
• Involves in detoxifi cation.
• Stores Ca2+ ions.
Function of golgi…
• Collecting, packaging and distribution of materials
• Manufacturing cellulose and non cellulose cell wall components such as pectin
• Produce lysosomes
functions of lysosomes…
• Digest food particles received by phagocytosis
• Transport residue material out of cell by exocytosis.
• Digest worn out organelles
• Autolysis causing cell death.
function of peroxisome
Detoxification of peroxides
• Photorespiration in plants
Where can we find specialized peroxisomes?
Specialized peroxysomes called glyoxysomes are found in fat storing tissues in plants.
Glyoxysomes converts fatty acids into sugar.
Where can we find specialized peroxisomes?
Specialized peroxysomes called glyoxysomes are found in fat storing tissues in plants.
Glyoxysomes converts fatty acids into sugar.
What does the mitochondrial matrix contain?
The inner most part of the organelle
is known as mitochondrial matrix, which consists of 70 s ribosomes circular DNA, molecule (mitochondrial DNA), phosphate granules and enzymes.
What are the enzymes of the mitochondria and what are their functions?
The matrix carries enzymes for the reactions in Krebs cycle (in cellular respiration). Further, cristae
composed of proteins and enzymes essential for electron transport chain and oxidative
phosphorylation.
What is the function of mitochondria?
• Synthesize ATP in aerobic respiration
• Involve in Photorespiration
What are found in the stroma of the chloroplast?
circular DNA (chloroplast DNA), 70s ribosomes, many enzymes, starch granules and lipid droplets.
What is the function of chloroplast?
Photosynthesis
What are the three components of the cytoskeleton?
• Microtubules
• Actin filaments or Microfilaments
• Intermediate filaments
Write another name for microtubules
Tubulin Polymers
Describe the structure of microtubules
- Hollow tubes
- wall consists of 13 columns of tubulin molecules
What are the protein subunits of microtubules?
Tubulin
Write the main functions of microtubules
Maintenance of cell shape
Cell motility (as in cilia or flagella)
Chromosome movements in cell division
Organelle movement
Give another name for microfilaments
Actin filaments
Write the structure of microfilaments
Two intertwined strands of actin, each strand is a polymer of actin subunits
Write the protein subunit of microfilaments
Actin
Write the functions of microfilaments
Maintenance of cell shape (tension- bearing elements)
Changes in cell shape
Muscle contraction
Cytoplasmic streaming in plant cells
Cell motility (as in pseudopodia)
Cell division in animal cells (cleavage furrow formation)
Write the structure of intermediate filaments
Fibrous proteins supercoiled into thicker cables
Give the protein subunits of intermediate filaments
One of several different proteins (e.g. Keratin), depending on the cell type.
Write the functions of intermediate filaments
Maintaining of cell shape (tension-bearing elements)
Anchorage of nucleus and certain other organelles.
Formation of nuclear lamina
What are the functions of the cytoskeleton?
Provide strength to the cytoplasm
Anchorage organelles and cytosolic enzymes of the cell
Movement of cytoplasm, cytoplasmic streaming, positioned organelles and move chromosomes when necessary
Maintain the shape of the cell (mainly in animal cells)
Describe the similarities between cilia and flagella
Cilia and flagella share a common structure.
They are made of microtubules, with a 9+2 structure (Nine doublets of microtubules are arranged in a ring, with two single
microtubules in its center).
They are covered by plasma membrane and bound to a basal body which anchors the cilium or flagellum to the cell. The Basal body has 9 + 0 arrangement (no microtubules in its center)
Describe the differences between cilia and flagella
Flagella are long elongated structures and Cilia are short cellular projections that are often organized in rows.
Cilia are more numerous than flagella on the cell surface.
What are the functions of cilia and flagella?
Act as locomotor appendages
Can move fluid over the surface of the tissue
Cilia lining in oviducts help move an egg toward the uterus
Describe the structure of a centriole
Centriole is made up of cylindrically arranged microtubules which are non membrane bounded subcellular component present only in animal cells.
Each centriole composed of nine sets of triplet microtubules arranged in a ring (9+0).
A pair of centrioles which arranged perpendicular to each other are located in a region called centrosome near the
nucleus.
Write the functions of a centriole
Produce aster and spindle in cell division
Describe the structure of a central vacuole
Central vacuole is a large structure, bound by tonoplast, filled with liquid called cell sap found in plant cells.
The composition of sap differs from cytosol and it contains water, ions such as Potassium and Chloride and sometimes water soluble colored pigments such as anthocyanin.
State the functions of a central vacuole
Stores water and other materials such as sugars, ions and pigments.
Maintains water balance of the cell
Gives turgidity and support to cell.
Produce colours in some plants with sap pigments
Stores soluble substances needed for cellular activities.
what is the extracellular structure of plant cells?
Cell Wall
Describe the nature of the cell wall of different types of organisms
Animal cells do not have cell walls.
Prokaryotes, fungi and some protists also have a thin and flexible cell wall
What is the plant cell wall made out of?
The chemical composition of the wall greatly varies from species to species and even from one cell type to another even in the same plant.
Nevertheless in Plants, cell wall is generally made up of cellulose, pectin, hemicellulose, lignin and suberin (in some
plant cells only).
What are the two types of cell walls plants generate?
Primary Cell Wall
Secondary Cell Wall
What’s the first cell wall secreted by young cells?
Primary cell wall
What’s the first cell wall secreted by young cells?
Primary cell wall
What is the cell wall laid down in plant cell division?
Primary cell wall
What is the thin layer just outside the primary wall?
thin layer (middle lamella)
What is the middle lamella rich in?
sticky polysaccharides called pectins (magnesium and calcium pectate)
Write the function of the middle lamella
Middle lamella glues adjacent cells together
How is a secondary cell wall generated?
Due to the deposition of hardening substances on the primary wall a secondary cell wall is generated secondarily
Describe the nature of the primary cell wall
Primary cell wall is permeable, relatively thin, flexible, composed mainly of cellulose fibers which are laid unevenly running through the extracellular matrix (middle lamella)Water can move freely through the free spaces of cell wall
Describe the nature of the secondary cell wall
Secondary cell wall lies between plasma membrane and primary cell wall. It contains several layers of hard materials, forming a rigid structure.
In addition to cellulose, impermeable substances such as lignin and suberin are also incorporated in to the secondary wall.
Lignin cement anchors cellulose fibers together providing hard and rigid matrix, giving the cell wall an extra support.
Why does the cell wall have pits?
Cell wall has pits through which cytoplasm of adjoining cells join through plasmodesmata
Write the functions of the cell wall
• Protection and support
• Allows development of turgidity when water enters the cell
• Prevents bursting during turgidity
• Limits and control cell growth
• Component of appoplast pathway
• Maintaining cell shape
• hold the plant up against the force of gravity
What are cell junctions?
Cell junctions are structures at which neighboring plasma membranes are joined.
They are also interact and communicate via sites of direct physical contacts.
What are cell junctions?
Cell junctions are structures at which neighboring plasma membranes are joined.
They are also interact and communicate via sites of direct physical contacts.
What are the functions of cell junctions
• Connects the internal chemical environment of adjacent cells.
• Cell junctions are structures at which cytoplasm of adjoining cells are joined.
What are the three types of cell junctions in animal cells
Tight junctions – connect the plasma membranes of adjacent cells tightly bound by specific proteins forming continuous seals around the cells. Prevent leakages of extracellular fluids through intercellular space.
Desmosomes/Anchor junctions – mechanically attach the cytoskeletons of adjoining cells by intermediate fi laments for strong binding.
Gap junctions /Communicating junctions – provide cytoplasmic channels from one cell to an adjacent cell. Gap junctions consists of special membrane proteins that surround the pore through which ions, sugars amino acids may pass.
They allow signal and material exchange between adjacent cells through direct connections.
Give examples for tight junction
skin epithelium
What are examples for Desmosomes/Anchor junctions
muscle tissue
Give an example for Gap junctions /Communicating junctions
Heart muscles
Animal embryo
What is plasmodesmata?
Microscopic channels which runs through plant cell walls.
They are cytoplasmic living connections between cytoplasm of adjoining cells. These are membrane lined channels filled with cytoplasm
What do animal cell walls have even though they lack cell walls
an extracellular matrix
Write the main components of the ECM
glycoproteins and other carbohydrates containing molecules secreted by the cells
What is the most abundant glycoprotein in the ECM
collagen which forms strong fibres outside the cell
How are collagen fibers located in the ECM?
The collagen fibres are embedded in a network woven out of proteoglycan secreted by cells
what are the functions of the ECM?
• Forms a protective layer over the cell surface
• Linking extra cellular matrix and cytoskeleton.
• Influences the cell behavior by Involving in the mechanical and chemical signaling
What is the end product of the cell cycle ?
At the end of the cell division, two genetically identical daughter cells resembling the parent cell are produced in mitosis.
What are the two major phases in the eukaryotic cell cycle?
• Interphase
• Mitotic phase/ M-phase
What is the longer phase of the cell cycle?
Interphase
What phase covers about 90% of the cell cycle
Interphase
What are the three phases the interphase can be divided into?
• G1 phase (first gap phase)
• S phase (synthetic phase)
• G2 phase (second gap phase)
What occurs in the G1 phase?
In this phase synthesis of proteins and production of cellular organelles leading to cell growth occur.
Proteins essential for S phase are produced during this phase.
What occurs in the S phase?
DNA replication occurs and synthesis of histone proteins takes place.
DNA wind around histone beads and form chromatin.
What happens in the G1 phase?
Cells continue to grow through protein synthesis as well as cellular organelles.
Proteins essential for mitotic phase will be synthesized. Duplication of centrosomes takes place.
Where are cell cycle-controlling checkpoints available?
G1, G2 and M phases
What do the cell cycle controlling checkpoints ensure?
they ensure that the cell is ready for moving into upcoming phases of cell division
What are the cells in the G0 phase of the cell cycle?
nerve cells
muscle cells.
What portion of the cell cycle does the mitotic phase cover?
10%
What does the mitotic phase of the cell cycle involve?
mitosis
cytokinesis
What does the process of mitosis give rise to?
two genetically identical daughter nuclei from a mother nucleus
What are the five stages of mitosis?
prophase
prometaphase
metaphase,
anaphase
telophase
What are the activities taking place in the prophase?
- Chromatin fibers get condensed by shortening and thickening and transformed into chromosomes.
*As a result chromosomes will be visible through light microscope. - Nucleoli get disappeared
- chromosomes appear with two sister chromatids attached at the centromere.
*Chromosomal arms of sister chromatids attached by special proteins called cohesion. - The formation of mitotic spindles begins
*Spindle include centrosomes, the spindle microtubules and the aster.
*Centrosomes move toward opposite poles of the cell - lengthening of microtubules between them.
What take place during prometaphase of mitosis?
- The nuclear envelope fragments.
- Chromosomes get even more condensed.
- A special protein called kinetochore attaches the sister chromatids of each chromosome at their centromere
- Some of the microtubules that attach to the kinetochore of the chromosomes move the chromosomes back and forth.
- Microtubules which are not attached to the kinetochore interact with those from the opposite poles.
What takes place during the metaphase of the mitotic cell division?
*Centrosomes reach the opposite poles.
*The chromosomes have arrived to a place called metaphase plate which is located in equal distance from each pole.
*The centromeres of all chromosomes are located in the metaphase plate.
*At the end of this phase, each chromosome of the cell get attached to the kinetochore microtubule at their centromere
and aligned at the metaphase plate.
What are the events taking place during the anaphase?
*Sister chromatids are separated at the centromere
*Microtubules attached to kinetochore get shorten and pull sister chromatids towards the opposite poles.
*Cell elongates as the non kinetochore microtubules are lengthen.
*By the end of anaphase equal and complete set of chromosomes found at each pole of the cell.
What are the events taking place during the telophase of the cell division?
- Nuclear envelope reforms around each set of chromosomes at opposite poles.
*Nucleoli reappears.
*Spindle microtubules get depolymerized.
*Chromosomes unwind and become less condense to form chromatin.
*Two genetically identical daughter nuclei are formed.
What takes place during cytokinesis process?
The division of the cytoplasm starts at the end of the telophase. Therefore at the end of the mitosis two genetically identical daughter cells are produced.
In animal cells, what is formed?
a cleavage furrow forms.
This produces two genetically identical daughter cells.
In plant cells, what is formed?
cell plate forms as a result of vesicle produced by golgi apparatus.
This divides the cytoplasm in to two and generates two genetically identical daughter cells
to the parent cell.
What are the significances of mitosis?
- Maintains the genetic stability
- Growth and development
- Cell repair, replacement and regeneration
- Asexual reproduction
What is the result of meiosis?
four haploid, genetically non identical daughter nuclei, from a diploid mother nucleus.
What does meiosis involve?
Meiosis I
Meiosis II.
What is the reduction division in meiosis?
Meiosis I
What stage of cell division of meiosis is similar to mitosis?
Meiosis II
What do each stage of meiosis include?
prophase
metaphase
anaphase
telophase.
What happens during meiosis of cell division?
Before meiosis one cell is in interphase, during S phase of the interphase DNA replication occur.
What happens during the prophase 1 of meiosis 1?
Cell enters to the prophase from interphase.
Chromosomes begin to condense.
Nucleolus begins to disappear.
Next the formation of zipper like structure called the synaptonemal complex by a specific proteins holds two homolg tightly together.
The pairing and physical connection of homologous chromosomes is called synapsis.
During synapsis part of the DNA molecule of non-sister chromatids paired homologous chromosomes break, exchange and rejoin at corresponding point. This process is called crossing over.
These points of crossing over become visible as chiasmata after the synaptonemal complex dissembles and the homologous chromosomes slightly apart from each other.
Nuclear envelop breaks.
Centrosomes move towards opposite poles forming spindle in animal cells.
The kinetochore of each homologue attach to microtubule from one pole or the other.
The homologous pair then moves toward the metaphase plate.
What events take place during metaphase 1?
*The pair of homologous chromosomes get arranged on the metaphase plate with one chromosome of each pair faces each pole.
*Both chromatids of a homologue are attached to kinetochore microtubules from one pole and those of the other homolog are attached to kinetochore microtubules from the opposite pole.
*Homologous chromosome arrange randomly at metaphase plate.
What events take place during Anaphase 1?
*Kinetochore microtubules of the spindle get shorten.
*Homologous pair separates and one chromosome of each pair moves towards the opposite pole.
*Sister chromatids of each chromosome remain attached at the centromere and move as a single unit towards
the same pole.
What takes place during telophase 1?
One complete haploid set of chromosomes accumulate at each pole.
Nuclear envelope reforms around each set of chromosomes.
Nucleoli reappear.
Spindle disintegrates.
Chromosomes decondensed into chromatin.
Genetically non identical, haploid, two daughter nuclei are formed within one cell.
What happens during cytokinesis?
Usually occurs simultaneously with telophase I.
Genetically non identical, haploid, two daughter cells are formed.
In animal cells, cleavage furrow is formed. In plant cells a cell plate is formed.
Does DNA replication occur in cytokinesis?
No
What takes place during meiosis 2 prophase?
Centrosomes start producing spindle apparatus (spindle fibers, aster centrosome).
Chromatin fibers condense and produce chromosomes with two sister chromatids.
Nuclear envelope breaks down into fragments.
Nucleolus disappears.
During the late prophase II centromere of the chromosomes are moved to the metaphase II plate.
What takes place during metaphase 2?
All Chromosomes get attached to the microtubules at their centromere and aligned on the metaphase plate.
Kinetochores of sister chromatids are attached to microtubules extending from both poles.
Due to the crossing over in meiosis I, the two sister chromatids of each chromosome are not genetically identical.
Meiosis II usually takes place in the perpendicular direction of Meiosis I. Therefore, metaphase plate of meiosis II is perpendicular to the metaphase plate of meiosis I.
What takes place during Anaphase 2?
Due to the breakdown of proteins attaching sister chromatids, they are separated at centromere.
As a result of shortening of microtubules , sister chromatids of each chromosome move towards opposite poles.
What takes place during telophase 2?
Nuclear envelope and nucleolus reform.
Chromosomes decondense into chromatin.
Spindle disassembles.
Genetically non identical, haploid, four daughter nuclei are formed from one parent cell.
What takes place during cytokinesis?
Cytokinesis occurs as in mitosis.
Genetically non identical, haploid, four daughter cells are formed.
These four daughter cells are not even identical to their parent cell.
Centrosomes or centrioles are not available in plant cells.
However, spindle is formed during cell division from accumulated microtubule complex.
What is the significance of meiosis?
• Maintains the constant number of chromosomes through generations in sexually reproducing species.
• Produce new genetic variations leading to evolution.
• Genetic variation occurs due to crossing over ,recombination and independent assortment.
What is the cell division controlled by?
Cell division is driven by external and internal factors.
They may be chemical or physical factors
What are the features of the cancer cells?
Cancer cells do not respond to normally to the body’s control mechanism
They divide excessively and invade other tissues. If unchecked they can kill the organism.
Cancer cells do not consider the normal signals that regulate the cell cycle.
They do not need growth factors.
They may make required growth factors themselves or giving signals to continue cell cycle without growth factors.
Another possibly is an abnormal cell cycle control system.
What takes place during transformation?
a single cell in a tissue undergoes transformation
The process converts a normal cell to abnormal cell.
If the body does not recognize an abnormal cell, what happens?
It may leads to proliferation of cells
formation of a tumor.
What are they called if the abnormal cells remain at the original site?
benign tumor
What is the difference between the benign tumor and malignant tumor?
Most benign tumors do not cause serious problems and can be completely removed by a surgery.
A malignant tumor becomes invasive and attack one or more organs. An
individual with a malignant tumor is said to have a cancer.
Describe the process of metastasis?
A few tumor cells may separate from the original tumor, enter blood vessels or lymph vessels and
They also would travel to other parts of the body.
They may proliferate and form a new tumor.
This spread of cancer cells to locations distant from their original site is called metastasis.
How are the galls in plants caused by?
Due to uncontrolled mitotic division of plant cell.
The plant cell division is controlled by maintaining a proper balance between plant growth regulators such as auxins and cytokinins.
When this balance is lost plant cells produce undifferentiated mass of cells.
How are galls formed?
Bumbs and growths that develop on different parts of plants namely galls are formed after
being invaded by some very unique organisms.
What are the range of causes of galls?
viruses
fungi
bacteria
Insects
Mites. (FIB MV)
What is the action of the gall causers?
Usually the gall causers in some way attack or penetrate the plants growing tissues
This causes the host to reorganize its cells and to develop an abnormal growth.
What is the difference between anabolic and catabolic reactions?
CATABOLIC REACTIONS:
Catabolism is breaking down of complex molecules into simple molecules by releasing free energy. Therefore it is an exergonic reaction.
ANABOLIC REACTIONS:
*Anabolism is making complex molecules from the simple molecules by absorbing free energy. Hence it is
an endergonic reaction.
*Biochemical reactions involved in usage of energy released by catabolic reactions in living system are called as anabolic reactions.
What is the difference between anabolic and catabolic reactions?
CATABOLIC REACTIONS:
Catabolism is breaking down of complex molecules into simple molecules by releasing free energy. Therefore it is an exergonic reaction.
ANABOLIC REACTIONS:
*Anabolism is making complex molecules from the simple molecules by absorbing free energy. Hence it is
an endergonic reaction.
*Biochemical reactions involved in usage of energy released by catabolic reactions in living system are called as anabolic reactions.
What are the processes in which energy is required?
• Synthesis of substances
• Active transport across plasma membrane
• Transmission of nerve impulses
• Muscle contraction
• Beating of cilia and flagella
• Bioluminescence
• Electrical discharges (SYTEM BBE)
What are the steps involved in the overall idea of energy relations in living systems on biosphere?
• Energy flows into biological systems from the environment through solar radiation. (Primary energy source is the Sun)
• Light energy is captured in the cells having photosynthetic pigments (chlorophyll) by the process of photosynthesis and stored as chemical energy in the organic compounds such as carbohydrates.
• Captured energy in organic food is transformed into chemical energy in ATP by a process called cellular respiration.
• The energy stored in ATP is utilized in various energy requiring processes.
What does the ATP consist of?
• Ribose- sugar
• Adenine - nitrogenous base
• A chain of three phosphate groups.
What is produced during the hydrolysis of ATP?
ADP and Pi are produced
As a result, very high energy is released.
When ATP is hydrolyzed, what is the free energy yield of each of the phosphate groups?
-30.5kJ/mol
What are the features of ATP?
Most biological reactions use the energy released during breaking of the terminal phosphate bond.
ATP is mobile.
Therefore it can carry energy to anywhere in the cell, for any energy consuming reaction.
What are the three forms of synthesis of ATP?
*Photophosphorylation
*Substrate phosphorylation
*Oxidative phosphorylation
What are the two methods of phosphorylation in cellular respiration?
Substrate phosphorylation
Oxidative phosphorylation
What are the different forms by which ATP is used in the living cells?
What are the different forms by which ATP is used in the living cells?
light
heat
chemical energy
mechanical energy
electricity
How is ATP used in light?
used in bioluminescence
How is ATP used in heat?
In maintaining body temperature
How is ATP used in chemical energy?
In synthesis of various compounds
How is ATP used in mechanical energy?
Used in muscle contraction
How is ATP used in electricity?
Used in conveying electrical impulses
What are the features of enzymes?
Enzymes are highly specific to the substrate (substrate specific)
Enzymes possess active sites where the reaction takes place.
They are not being used up during the reaction.
Enzymes are biological catalysts. They lower the activation energy of the reaction they catalyze (increases the rate of reaction).
Their presence does not alter the nature or properties of the end product of any reaction.
The rate of enzyme activity is affected by pH, temperature and substrate concentrations.
Some enzymes need non-proteinuos components to catalyze the reaction which are known as cofactors.
Most enzymes are heat liable/ sensitive
Most of the enzymes are globular proteins.
Explain the specificity of the enzyme
The specificity of an enzyme results from its shape. The substrate binds to a specific region of the enzyme. This
region is called the active site. The active site is formed by only a few amino acids.
Other amino acids are needed to maintain the shape of the enzyme molecule. The shape of the active site is complementary to the shape of the specific substrate of the enzyme, and hence important in the substrate specificity of the enzyme.
The shape of the active site of an enzyme is not always fully complementary to its substrate.
Explain the induced fit mechanism
The shape of the active site of an enzyme is not always fully complementary to its substrate. As
enzymes are not rigid structures, the interactions between substrate and active site
may slightly change the shape of the active site, so that the substrate and the active site
become complementary to each other
What does the tight fit in induced fit mechanism ensure?
The tight fit not only brings the substrate molecules and the active site close to each other, but
also ensures the correct orientation of the molecules to help the reaction to proceed and catalyzes the conversion of substrate to product.
Thereafter, the product departs from the active site of the enzyme.
The enzyme is then free to take another substrate molecule into its active site.
What are the two ways by which the cofactors bind to the enzymes?
Some tightly bind, and remain permanently
others loosely bind temporarily
What are the examples of organic cofactors?
NAD, FAD and biotin
What are inorganic cofactors?
Zn2+, Fe2+, Cu2+
What are factors affecting the rate of enzymatic reaction?
- Temperature
- pH
- Substrate concentration
- Enzyme concentration
- Inhibitors
What happens when the temperature increases?
Increase in temperature increases molecular motion.
Therefore the speed of the moving molecules of both enzymes as well as the substrate will be accelerated. This
will enhance the colliding probability for both enzyme active sites and substrate molecules
What results in greater chances of reaction occurring?
More collision between the enzyme active sites and substrate molecules
generate greater chances for the reaction to occur.
Explain about the optimum temperature?
This can continue up to a certain point, after which there is a rapid decline in enzyme activity.
What is the optimum point of organisms?
This may vary from organism to organism.
e.g. most of the human enzymes have optimum temperature around the body temperature (35˚C-40˚C).
Optimum temperature of bacteria in hot springs is about 70˚C.
When the temperature increases beyond the optimum temperature, what bonds are disrupted?
the hydrogen bonds, ionic and other weak chemical bonds of enzyme active sites may be disrupted.
What does the disruption of bonds of enzymes as a result of high temperature result in?
This will result a change in the shape of the active site of enzyme which will alter the complementary nature of the active site of enzyme molecules.
Therefore, the complementary binding of enzyme active sites and substrate molecules will be prevented.
The above event is called as denaturation of enzyme molecules.
What happens when the temperature is increased beyond the optimum temperature?
Therefore the rate of enzyme catalyzed reaction will start to decline when the temperature increases beyond the optimum temperature and stops completely at certain temperature, although rate of collision will keep on increasing.
What happens in alteration of Ph below or above the optimum pH level?
The alteration in pH above or below the optimum pH may lead to decline in enzyme activity.
This is due to the alteration of chemical bonds involving in formation of enzyme substrate complex
In most enzymes, what is the optimum pH level?
6-8
What is the optimum pH of pepsin?
2
What is the optimum pH of trypsin?
8
What happens when the substrate concentration is increased?
Increasing substrate concentration increases the probability of collision between the enzyme and substrate molecules with correct orientation.
However the enzyme molecules will be saturated after a particular concentration and therefore there will not
be any further increase in the rate of reaction.
How do enzyme inhibitors bind?
selectively bind permanently or temporarily
Name the irreversible inhibitors
toxins and poisons
Name the reversible inhibitors?
drugs used against microbes
Describe the features of competitive inhibitors.
Most of these are reversible inhibitors.
These chemicals resemble the shape and nature of the substrate.
Therefore they compete with the substrate selectively for the active site of certain enzymes
As a result of the above, the number of active sites available for the enzymes may decline and therefore reduces the rate of enzyme catalyzed reactions.
What is an example for competitive inhibitors?
Protease inhibitor of drugs against HIV.-change
What are the features of non competitive inhibitors?
These chemicals do not compete with substrate molecules.
They interrupt enzymatic reaction by binding to a part of the enzyme other than the active site.
This causes the enzyme molecule to change its shape in such a way that the active site becomes less
effective for the formation of enzyme substrate complex.
What are the three types of allosteric regulations of enzymes?
a.) Allosteric activation and inhibition
b) cooperativity
c) Feedback inhibition
What do molecules that naturally regulate enzyme activity behave as?
like reversible non-competitive inhibitors.
What are the two types of regulatory molecules?
activators or
inhibitors)
Describe the basic activity of the allosteric regulation of the enzymes?
Regulatory molecules (either activators or inhibitors) bind to specific regulatory sites elsewhere (other than the active site) of
the molecule via non-covalent interactions and affect the shape and function of the enzyme.
It may result in either inhibition or stimulation of an enzyme activity.
Give an example of allosteric activation and inhibition
ADP function as allosteric activator bind to the enzyme and stimulates the production of ATP by catabolism.
If the supply of ATP exceed demand catabolism slows down as ATP bind to the same enzyme as inhibitor.
What events take place during allosteric activation and inhibition?
*Most enzymes regulated by allosteric regulation are made from two or more subunits.
*Each sub unit composed of a polypeptide chain with its own active site.
*The entire complex oscillates between two different shapes one catalyzing active and other inactive.
*In this two forms regulatory molecules bind to a regulatory site called allosteric site, often located where subunits join.
What events take place during cooperativity?
This is another type of allosteric activation.
Binding of one substrate molecule can stimulate binding or activity at other active site.
Thereby increase the catalytic activity.
What is an example for cooperativity?
hemoglobin (not an enzyme) is made up of four subunits each with an O2 binding site.
The binding of a one molecule of O2 to one binding site increases the affinity for O2 of the remaining binding site.
What takes place during the feedback inhibition?
In feedback inhibition, a metabolic pathway is stopped by the inhibitory binding of its end product of a process to an enzyme.
Thereby limit the production of more end products than required and thus wasting chemical resources.
What is an example for feedback inhibition?
DP function as allosteric activator and stimulates the production of ATP during
the catabolism.
In case ATP supply exceeds demand, catabolism slows down as ATP
molecules function as allosteric inhibitor.
Energy needed for all living processes is obtained directly from ATP. ATP is mainly
produced by a process call ed cellular respiration, in living cells.
What is the global importance of photosynthesis?
• All life on earth depends on photosynthesis, directly or indirectly
• Fulfi ll both carbon and energy requirements of organisms
• Provide O2 for respiration of aerobic organisms
• Maintain O
* and CO2 balance in the atmosphere
• Production of fossil fuel
• Maintenance of global temperature
What are the two major stages of photosynthesis?
• Light-dependent reaction
• Calvin cycle
What are the two types of photosynthetic mechanisms (path ways) based on the number of C atoms of the first stable product of the CO2 fixation?
• C3 Mechanism – No of C atom of the first stable compound is three
• C4 Mechanism – No of C atom of the first stable compound is four
Where does the light dependent reaction of photosynthesis taker place in?
In the membrane system of thylakoids.
What is the function of chlorophyl a?
key light capturing pigment and they participate directly in the light reaction of photosynthesis
It is is more effective for blue and red light.
What is the function of chlorophyl b and carotenoids?
They are effective in absorption of specific range wavelengths of corresponding to different colours.
carotenoids ========> photoprotection
What takes place in photoprotection?
absorption and dissipation of excessive light energy, if not that excessive light may
cause damage to the chlorophylls or interact with oxygen and form reactive oxidative
molecules which are dangerous to the cell.
What is the result of the linear electron flow?
ATP
NADP
What are the two types of photosystems in the thylakoid?
Photosystem I (PS I) - absorb light at 700nm wave length effectively
photosystem II (PS II) - P680 which absorbs light having a wavelength of 680 nm.
What is the difference between the linear and the cyclic electron flow?
In linear electron flow, Splitting of water takes place as a result of an enzyme catalyzed reaction and yields O2
(g), H+ ions and electrons.
During the process of linear electron chain, by what method is ATP synthesized by?
By photophosphorylation
What is the difference between the linear electron flow and the cyclic electron flow?
This occurs in photosystem I but not in Photosystem II. Here some photoexcited
electrons uses alternative cyclic pathway.
This produces ATP but not NADPH and Oxygen are released, unlike linear electron flow, unlike linear electron flow.
What are the three steps of the Calvin cycle?
Carboxylation (Carbon fixation)
Reduction
Regeneration of carbon dioxide acceptor
What are the events taking place during carbon fixation?
The CO2 acceptor is a 5 C sugar, Ribulose bisphosphate (RuBP).
The addition of CO2 to a RuBP is called carboxylation.
The enzyme involves in this reaction is RuBP carboxylase oxygenase or Rubisco.
The first product of RuBP carboxylation is a 6C molecule which is unstable and breaks down immediately in to two molecules of 3-phosphoglycerate (3-PGA).
This is the first stable product of photosynthesis. (3-PGA)
The enzyme RuBP carboxylase oxygenase (Rubisco) is present in large amounts in the chloroplast stroma.
What are the events taking place during the reduction phase?
1,3-Bisphosphoglycerate will be reduced to Glyceraldehyde 3- phosphate (G3P) through step by step.
Enzyme catalyzed reactions utilizing NADPH and ATP from light reaction.
G3P will act as a precursor for carbohydrate synthesis (glucose).
What events take place during regeneration of RuBP?
RuBP is regenerated by undergoing a series of complex reactions.
This process uses energy from ATP generated in light reaction.
What is the result of photorespiration?
The oxygenase reaction forms just one molecule of 3-PGA plus a two carbon product, 2-phosphoglycolate
What is the disadvantage of photorespiration?
2-phosphoglycolate which is of no immediate use in the Calvin cycle and in higher concentrations it is toxic for the plant
Photorespiration is not only energy demanding, but furthermore leads to a net loss of CO2.
Each time Rubisco reacts with O2 instead of CO2 the plants makes 50% less 3-PGA than it would have done if CO2 had been used.
This potentially eliminates the net gain in photosynthetic carbon and loose the productivity
What is the photorespiratory pathway
The photorespiratory pathway involves enzymes in the chloroplasts, peroxisome and mitochondria.
What are the conditions within a leaf that favor wasteful process of photorespiration?
The CO2. required for photosynthesis enters a leaf via stomata. However, stomata are also the main avenues of transpiration. On a hot, dry day, most plants close their stomata in order to conserves water.
At the same time O2. released from the light reactions begins to increase and this leads to further reduction of (CO2.) to (O2) ratio in the cytosol
photorespiration is favored under what conditions?
high temperature
dryness
high light intensities
How are plants developed to cope with the situation of photorespiration?
during the evolution that resulted a most successful solution to concentrate CO2 provided by C4 photosynthetic pathway.
around Rubisco.
What are the anatomical modifications of C4 pathway?
1 ) The establishment of C4 photosynthetic pathway includes several biochemical and anatomical modifications that allow plants with this pathway to concentrate CO2 at the site of Rubisco.
Thereby its oxygenase reaction and the following photorespiration are largely repressed in C4 plants.
2) In most C4 plants the CO2 concentration mechanism is achieved by a division of labor between two distinct specialized leaf cell types, the mesophyll and the bundle sheath cells.
3) Compared to C3 plants the bundle sheath cells of C4 plants have expanded physiological functions.
4) This is reflected by the enlargement and higher organelle content of these cells in C4 species. For the efficient function of the C4 pathway a close contact between mesophyll and bundle sheath cells are tightly interconnected to each other by high numbers of plasmodesmata.
5) The bundle sheath cells enclose the vascular bundles and are themselves surrounded by the mesophyll cells and this type of leaf anatomy was termed Kranz anatomy.
What are the steps involved in the C4 mechanism?
POMP
Describe the steps involved in the C4 control mechanism
*In the mesophyll cells of C4 plants CO2 is converted to bicarbonate by carbonic anhydrase and initially fixed by phosphoenolpyruvate carboxylase using PEP as CO2 acceptor.
*The resulting oxaloacetate (OAA) is composed of four carbon atoms, which is the basis for the name of this metabolic pathway.
*Oxaloacetate is rapidly converted to the more stable C4 acids malate or aspertate that diffuse to the bundle sheath cells.
Here, CO2 is released by decarboxylating enzymes and the released CO2 is refixed by Rubisco, which exclusively operates in the bundle sheath cells in C4 plants.
What is the difference between the chloroplasts in the bundle sheath cell and the mesophyll cell?
*Since chloroplasts of mesophyll cells carryout only light reaction, they are rich in grana.
*The grana of mesophyll chloroplasts are large and highly differentiated for light reaction. Bundle sheath chloroplasts possess a very few, less differentiated grana or grana are absent.
*Moreover, that PSII in the bundle sheath cells are depleted in order to lower oxygen production in these cells.
Why is PEP more efficient than RUBP Carboxylase?
- It reacts with bicarbonate (HCO-3) rather than with CO2’ The advantage of this is that there is a 50-fold higher concentration of HCO3- than CO2 in solution in the cytosol.
- It has no affinity for O2
Why is C4 pathway significant?
• Helps plants to improve the efficiency of CO2 fixation at lower CO2 concentrations by preventing the gateways for photorespiration by spatially separating Rubisco.
• In hot-dry climate, it is essential for the stomata to close to prevent water loss through transpiration. This reduces CO2 intake of particular plants. Therefore, plants in tropical zones or hot climate may suffer from CO2 deficiency. At lower CO2 concentrations, C4 mechanism increases the efficiency of photosynthesis by concentrating CO2 in the bundle sheath cells.
*C4 plants exhibit better water-use efficiency than C3 plants because of the CO2 concentration mechanism they can acquire enough CO2 even when keeping their stomata more closed. Thus water loss by transpiration is reduced.
*Since Rubisco can operate under high CO2 concentrations in the bundle sheath cells, it woks more efficiently than in C3 plants, consequently C4 plants need less of this enzyme, this leads to a better nitrogen-use efficiency of C4 compared to C3 plants.
What are the differences between C3 and C4 plants?
Representative species of C3 is Wheat, rice barley. In C4 Maize, sugarcane, grasses
Temperature optimum for photosynthesis ( 0C) of C3 is 15-25 and for C4 50% greater at 35 ˚C
CO2 fixation in C3 occurs once. In C4 Occurs twice, first in mesophyll cells, second in bundle sheath cells
CO2 acceptor in C3 is 5C, RuBP. In C4 3C, PEP mesophyll cells 5C RuBP in bundle sheath cells
CO2 fixing enzyme in C3 is rubisco and in C4 PEP carboxylase in mesophyll cells which is very efficient Rubisco in bundle sheath cells, working efficiently under high CO2 concentration
First product of CO2 fixation in C3 plants C3 acid, 3-phosphoglycerate (3-PGA). In C4 plants 4C acid, oxaloacetate (OAA)
Leaf anatomy of C3 plants Bundle sheath cells, if present, are not green (non photosynthetic), photosynthesis occurs in Mesophyll
cells. In C4 plants Kranz anatomy with photosynthesis occurring in both mesophyll cells and bundle sheath cells
Productivity of C3 plants, the yield is usually lower. In C4 plants the yield is usually high.
What are the factors affecting photosynthesis?
light intensity
CO2 concentration
temperature
water
pollutants
inhibitors
Under normal conditions, what is the major limiting factor of photosynthesis?
CO2
Increase in photosynthetic rate is achieved by increasing CO2 concentration. For example some greenhouse crops such as tomatoes are grown in CO2 enriched atmosphere.
What are the biochemical modifications of the C4 pathway?
1.) Since Rubisco can operate under high CO2 concentrations in the bundle sheath cells, it works more efficiently than in C3 plants. Because of the CO2 concentration mechanism .
they can acquire enough CO2 even when keeping their stomata more closed and minimize the water loss by transpiration.
2) PEP efficiency
What are the 3 main steps of aerobic respiration?
a) Glycolysis
b) Pyruvate oxidation and citric acid cycle (Kreb’s cycle)
c) oxidative phosphorylation (Electron transport chain)
Give an equation for aerobic respiration
C6H12O6 + 6O2(g) ————————–> 6CO2(g) + 6H2O + Energy (ATP+ heat)
