The document discusses cell membranes and their structure and composition. It notes that membranes are made of a bilayer of polar lipids, including sphingomyelin, glycerolipids, and cholesterol. It describes how the length and saturation of fatty acid chains and the presence of cholesterol affect membrane fluidity. Homeothermic organisms regulate membrane fluidity through adaptations like changing fatty acid chain length and saturation. The document also discusses asymmetries in membrane composition and lipid movement across membranes. Integral membrane proteins span or are embedded in the bilayer, and are anchored via interactions with specific lipid groups.
INTRODUCTION
TERMENOLOGY
SITES OF HOLLIDAY JUNCTION
HOMOLOGOUS RECOMBINATION
HOLLIDAY MODEL
DOUBEL STRAND BREAK MODEL
IN PROKAYOTIC RECOMBINATION
IN EUKARYOTIC RECOMBINATION
SITE SPECIFIC RECOMBINATION
SERINE RECOMBINATION
TYROSINE RECOMBINATION
TRANSPOSITION
ILLEGITIMATE RECOMBINATION
CONCLUSION
REFRENCES
Definition - Rolling circle replication is a process of unidirectional nucleic acid replication.
* can rapidly synthesize multiple copies of circular molecules of DNA or RNA, such as plasmids.
* Eucaryotic also replicate.
* widely used in molecular biology & biomedical
nanotechnology, especially in the field of
biosensing (as a method of signal Amplification).
Steps:
Circular ds DNA will be “nicked”
3` end is elongated →Leading strand
5` end displaced → Lagging strand
made up of double stranded by OKAZAKI fragments.
4) Replication of both “ unnicked” and displaced ss DNA
5) Displaced DNA circulates and synthesis its own complementary strand.
Initation-- phosphate ends, by the action of:
a) Helicase
b) Topoisomerases
c) Single stranded binding proteins(SSBPs)
Elongation-OH group of broken strand, using the unbroken strand as a template. The polymerase will start to move in a circle for elongation, due to which it is named as Rolling Circle Model.
end will be displaced and will grow out like a waving thread.
Termination-* At the point of termination, the linear DNA molecule is cleaved from the circle resulting in a double stranded circular DNA molecule and a single- stranded linear DNA molecule.
* The linear single stranded molecule is circularized by the action of ligase and then replication to double stranded circular plasmid molecule.
Example- Conjugation of F+ and F- bacteria
Diagrammatic representation of Rolling circle
some Examples-Viral DNA
* Human herpes virus
* Human papilloma virus
* Geminivirus
Viral RNA
* pospiviridiae
* Avsunviridiae
Reference:- https://en. m. wikipedia.org
what- when- how.com
https//www.sciencedirect.com
www.slideshare.com
Genetics-notes.wikispace.com
you tube
Prescott 5th edition page.no: 236, 237
Brock biology of microorganism , page.no: 253,616
One of the first plausible models to account for the preceding observations was
formulated by Robin Holliday.
The key features of the Holliday model are the formation of heteroduplex DNA; the
creation of a cross bridge; its migration along the two heteroduplex strands,
termed branch migration; the occurrence of mismatch repair; and the
subsequent resolution, or splicing, of the intermediate structure to yield different
typesof recombinant molecules.
INTRODUCTION
TERMENOLOGY
SITES OF HOLLIDAY JUNCTION
HOMOLOGOUS RECOMBINATION
HOLLIDAY MODEL
DOUBEL STRAND BREAK MODEL
IN PROKAYOTIC RECOMBINATION
IN EUKARYOTIC RECOMBINATION
SITE SPECIFIC RECOMBINATION
SERINE RECOMBINATION
TYROSINE RECOMBINATION
TRANSPOSITION
ILLEGITIMATE RECOMBINATION
CONCLUSION
REFRENCES
Definition - Rolling circle replication is a process of unidirectional nucleic acid replication.
* can rapidly synthesize multiple copies of circular molecules of DNA or RNA, such as plasmids.
* Eucaryotic also replicate.
* widely used in molecular biology & biomedical
nanotechnology, especially in the field of
biosensing (as a method of signal Amplification).
Steps:
Circular ds DNA will be “nicked”
3` end is elongated →Leading strand
5` end displaced → Lagging strand
made up of double stranded by OKAZAKI fragments.
4) Replication of both “ unnicked” and displaced ss DNA
5) Displaced DNA circulates and synthesis its own complementary strand.
Initation-- phosphate ends, by the action of:
a) Helicase
b) Topoisomerases
c) Single stranded binding proteins(SSBPs)
Elongation-OH group of broken strand, using the unbroken strand as a template. The polymerase will start to move in a circle for elongation, due to which it is named as Rolling Circle Model.
end will be displaced and will grow out like a waving thread.
Termination-* At the point of termination, the linear DNA molecule is cleaved from the circle resulting in a double stranded circular DNA molecule and a single- stranded linear DNA molecule.
* The linear single stranded molecule is circularized by the action of ligase and then replication to double stranded circular plasmid molecule.
Example- Conjugation of F+ and F- bacteria
Diagrammatic representation of Rolling circle
some Examples-Viral DNA
* Human herpes virus
* Human papilloma virus
* Geminivirus
Viral RNA
* pospiviridiae
* Avsunviridiae
Reference:- https://en. m. wikipedia.org
what- when- how.com
https//www.sciencedirect.com
www.slideshare.com
Genetics-notes.wikispace.com
you tube
Prescott 5th edition page.no: 236, 237
Brock biology of microorganism , page.no: 253,616
One of the first plausible models to account for the preceding observations was
formulated by Robin Holliday.
The key features of the Holliday model are the formation of heteroduplex DNA; the
creation of a cross bridge; its migration along the two heteroduplex strands,
termed branch migration; the occurrence of mismatch repair; and the
subsequent resolution, or splicing, of the intermediate structure to yield different
typesof recombinant molecules.
Basics of Undergraduate/university fellows
Since, these chromosomes were discovered in the salivary gland cells, they are called
as "Salivary Gland Chromosomes".
The present name polytene chromosome was suggested by kollar due to the
occurrence of many chromonemata (DNA) in them.
Bridges (~1936) 1st constructed a salivary chromosome map of D melanogaster and
found 5000 special bands in polytene chromosomes.
you can find here several multiple choice questions referring to this topic that come from the IGCSE exams or some definitions from the IGCSE syllabus.
http://biodeluna.wordpress.com/
Genetic engineering - Searching for a target for the treatment of atheroscle...Xplore Health
Protocol for youngsters to carry out a bacterial transformation in a lab. The protocol follows a line of biomedical research which focuses on the study of a potential therapeutic target that could be recognised by a drug against atherosclerosis. The experiment protocol is an opportunity for science centres, museums and schools to replicate a real experiment done in a real lab doing research on drug discovery.
Basics of Undergraduate/university fellows
Since, these chromosomes were discovered in the salivary gland cells, they are called
as "Salivary Gland Chromosomes".
The present name polytene chromosome was suggested by kollar due to the
occurrence of many chromonemata (DNA) in them.
Bridges (~1936) 1st constructed a salivary chromosome map of D melanogaster and
found 5000 special bands in polytene chromosomes.
you can find here several multiple choice questions referring to this topic that come from the IGCSE exams or some definitions from the IGCSE syllabus.
http://biodeluna.wordpress.com/
Genetic engineering - Searching for a target for the treatment of atheroscle...Xplore Health
Protocol for youngsters to carry out a bacterial transformation in a lab. The protocol follows a line of biomedical research which focuses on the study of a potential therapeutic target that could be recognised by a drug against atherosclerosis. The experiment protocol is an opportunity for science centres, museums and schools to replicate a real experiment done in a real lab doing research on drug discovery.
The structure of the cell membrane, the phospholipid layer distinguished to the break down of protein and the lipid layer. Their structural components and the molecular basis of it.
The current model of cellular membranes is called PB and J sandwich.pdfbhim1213
The current model of cellular membranes is called PB and J sandwich molecular mosaic fluid
mosaic plasma membrane Which characteristic apply to the phospholipid membrane? It is
primarily a hydrophobic bilayer. Phospholipids are amphipathic Proteins are imbedded within
the phospholipids. The imbedded molecules can move freely within the membrane All are
important characteristics of the Cholesterol molecules in the membrane act to modulate
temperature dependent viscosity and fluidity of the membrane. moderate the effects of a high fat
diet promote fluidity in the membrane. allow for better membrane compaction and integrity.
allow transport across the membrane. One important feature of membranes in the
endomembrane system is that they can move freely from cell to cell. freely bleb off of and then
onto other components of this network. they contain small pieces of independently replicating
DNA. they move from the trans side of the membrane to the cis side. t
Solution
1. Fluid mosaic model.
Fluid mosaic model for plasma membrane proposed by Jonathan Singer and Garth Nicolson is
universally acceoted model for plasma membrane.
2. All are important characteristics.
Phospholipid molecules are hydrophobic and amphipathic. Which means that posess polar head
and non polar tails.
Some of the protien molecules are embedded in the phospholipid layer and these moelcules are
free to move due to fluid nature of plasma membrane.
3. Allows better membrane compaction and integrity.
Cholesterol is an amphipathic molecule like phospholipids. It contains a hydrophilic and a
hydrophobic portion. Cholesterol\'s hydroxyl (OH) group aligns with the phosphate heads of the
phospholipids. The remaining portion of it tucks into the fatty acid portion of the membrane.
Because of the way cholesterol is shaped, part of the steroid ring (the four hydrocarbon rings in
between the hydroxyl group and the hydrocarbon \"tail\") is closely attracted to part of the fatty
acid chain on the nearest phospholipid. This helps slightly immobilize the outer surface of the
membrane and make it less soluble to very small water-soluble molecules that could otherwise
pass through more easily.
4. They contain transport enzymes..
Singer and Nicolson proposed the fluid mosaic model of the cell membr.pdfbrijeshagarwa329898l
Singer and Nicolson proposed the fluid mosaic model of the cell membrane The main type of
membrane lipids: phospholipids, glycolipids, and sterols could be represented with the
respectively membrane lipids phosphoglycerides, cerebrosides and cholesterol. In E. coli the
enzyme responsible for creating unsaturated bonds from saturated ones in the fatty adds of the
cell membrane is denaturize Substances that can readily pass through the cell membrane are
chemically hydrophobic or nonpolar in nature. Transmembrane proteins involved in detecting
external stimuli and relaying that Information to the cell are most likely receptor proteins. The
current understanding of the membranes of the cell is based on the fluid mosaic model. The
ability of some organisms to alter their membrane lipid composition in response to temperature is
known as homeoviscous adaptation The technique of transferring proteins from SDS-PAGE gels
onto a membrane and using labeled antibodies to identify particular proteins is known as western
blot Triglycerides are composed of three fatty acids attached to a molecule of glycerol
Solution
Ans. 1. True. They proposed the model in 1972, and were awarded Nobel prize for it.
Ans. 2. True
Phospholipids = phsophoglycerides
Sterol = cholesterol
Glycolipids are lipids containing covalently linked carbohydrate moieties.
Cerebrosides, also known as, glycosphingolipids, also contain glucose or galactose residues
linked to the ceramide (lipid) skeleton. Thus, cerebrosides are also glycolipid in nature because
have carbohydrate moieties linked to lipid.
Ans. 3. True
Fatty acid desaturase creates double bond (unsaturation) in fatty acids by removing two H-atoms
from adjacent carbo atoms in the chain.
Ans. 4. True
Since the lipid bilayer has a hydrophobic core, small, non-polar or hydrophobic molecules (for
example, CO2) can readily pass through it.
In contrast to it, polar or charged ion/ molecules or large molecules (non-polar as well as polar)
can’t pass through the membrane so efficiently.
Ans. 5. True
Receptor proteins need to bind an effector molecule at the extracellular face and transmit the
signal to cytoplasmic side of the cell. Thus, it shall be a transmembrane protein, i.e. a protein that
spans the lipid bilayer.
Ans. 6. True
Ans. 7. True
Many organism can change the lipid composition of the membrane depending of the
environmental temperature. The phenomenon being called “homeoviscous adaptation”.
For example, in winters, the membrane of a plant cell also retains the fluid-nature under freezing
conditions. Relatively larger abundance of cis-fatty acids, unsaturated fatty acid in the
phospholipids and steroids makes the membrane more fluid because both cis-form and
unsaturation makes the chain irregular-shaped and hinders the close packing of hydrophobic
core. So, such membrane retain fluidity even at very low temperatures.
Ans 8. True
Western blot detects specific protein through combined use of SDS-PAGE and immunoblotting
technique.
27. Factors that affect membrane fluidity: Length of the fatty acyl chains Degree of saturation of the fatty acyl chains Presence of cholesterol The rigid cholesterol ring system interferes with close packing of phospholipid fatty acid tails and thus inhibits transition from liquid crystal to crystalline state upon temperature decrease. At the same time, the rigid cholesterol makes the membrane somewhat less fluid.
28. The effect of fatty acid composition on membrane fluidity Two aspects: the length and the degree of un-saturation Membrane lipids often contain one saturated and on unsaturated fatty acids The effect of sterols on membrane fluidity Sterols – cholesterol and phytosterols. Sterols account for up to 50% of total membrane lipid on a molar basis The cholesterol molecules form hydrogen bonds with the oxygen atom on its neighboring phospholipid molecule The paradoxical effect of cholesterol : decreasing membrane fluidity at high temperature (due to the rigid “rings”) and increasing it at low temperature (by preventing regular arrangement of neighboring hydrocarbon tails) However, sterols decrease the permeability of a lipid bilayer, by plugging in the spaces between phospholipid molecules Most organisms can regulate membrane fluidity Poikelotherms (bacteria, fungus, plant, amphibians etc.) vs. homeotherms (warm-blooded animal) Homeoviscous adaptation – keeping the viscosity of the membrane about the same despite changes in temperature, by removing the terminal carbons to shorten the fatty acid molecules or introducing unsaturated bonds into the existing saturated fatty acid molecules (by e.g. E. coli desaturasae). Lipids of 18 carbon 70 o C -11 o C 76 o C 32 o C
41. α-helix is the major structural element of membrane-bound proteins
42.
43. Membrane lipids: the “mosaic” part of the model Freezing fracturing: quick frozen (in liquid nitrogen) and then subjected to a sharp blow of a diamond knife. E face (exoplasmic sicde) and P face (protoplasmic side) Membrane contain integral, peripheral, and lipid-anchored proteins Integral membrane proteins: contain ~20 aa hydrophobic transmembrane segment and hard to isolate or extract and need detergent treatment. Intergral monotopic proteins Transmembrane protein: singlepass multipass multi-subunit Glycophorin of erythrocyte Bacteriorhodopsin The hydropathy plot