Chapter 98 -- Part 1: DNA Replication in Eukaryotes
The prediction of the making of an exact replica of the DNA molecule by semiconservative replication was proven by Meselson and Stahl.
Each strand of the double helix contains a template for the creation of a new strand composed of T and C with G.
The origin of replication is where the two strands of DNA separate to form bubbles.
There are thousands of bubbles along the DNA molecule.
The process of replicating along the giant DNA molecule is sped up by bubbles.
The Y-shaped region where the new strands of DNA are elongating is at each end of the replication bubble.
All the bubbles come to an end.
The new strands of DNA are antiparallel.
The replication fork moves along the template strand to push the new strand from the 5' to the 3' direction.
The rate of elongation in humans is around 50 nucleotides per 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609-
The 3' end of a preexisting chain can only be added to by DNA polymerase.
TheRNA primer is a part of the preexisting chain.
The primer is made by joining togetherRNA nucleotides.
One of your cells can make a copy of its entire genome in a few hours.
The two original strands of DNA are different.
One strand is formed toward the replication fork in a linear fashion despite the fact that it builds both strands in the 5' to 3' direction.
This strand is called the leading strand.
The lagging strand forms in the direction away from the fork in a series of segments.
The fragments are long and will be joined into a single strand by the DNA ligase.
There are other genes that help in the replication of the DNA.
The double helix is twisted at the replication fork.
The parental strands are available as templates.
The two DNA strands are held apart by single-stranded binding proteins.
The tension on the tightly wound helix is lessened by breaking and rejoining the DNA strands.
There is a type of repair called mismatch repair that corrects errors.
The damaged parts of the DNA are excised.
The ends of the chromosomes are lost when the DNA replicates.
To protect against the loss of genes at the ends of the chromosomes, eukaryotes have special nonsense nucleotides at the ends of the chromosomes that repeat thousands of times.
The ends of the chromosomes are called telomeres.
Telomeres are created and maintained.
Every time the DNA is copied, the telomeres get shorter.
The clock may count cell divisions and cause the cell to stop dividing as it ages.
The process of making proteins has been worked out.
The triplet code in DNA is transcribed into a codon sequence inside the nucleus.
A strand of pre-RNA is processed in the nucleus.
The codon sequence leaves the nucleus and is translated into a polypeptide at the ribosome.
There is a sequence of nucleotides in a gene and a sequence of amino acids in aProtein.
The process by which the information in a DNA sequence is copied is called transcription.
There are three types ofRNA that are involved in the synthesis of the molecule.
When a sequence of DNA is expressed, one of two strands of DNA is copied into the messenger RNA.
Structural rRNA is involution in translation.
The ribosome is made up of two small and large subunits.
The ribosome has three binding sites, known as A, P, and E. A ribosome is a synthesis factory.
tRNA is shaped like a cloverleaf and has a binding site for two acids at one end.
The three stages of transcription are initiation, elongation and termination.
The initiation begins when the RNA polymerase recognizes and binding to the DNA at the promoter region.
The promoter tells the promoter where to begin the transcription.
A key area within the promoter, the TATA box, is recognized by a collection of transcription factors.
The completed assembly of transcription factors is called a transcription initiation complex.
The DNA template begins to be transcribed once the promoter is attached.
Elongation of the strand continues as the strand is added to a growing chain.
The base pair rules are C with G and A with U.
A transcription unit is the stretch of DNA that is transcribed into a molecule.
The codons in each unit are used to code for specific acids.
A single gene can be transcribed into a large amount of mRNA in a matter of minutes.
The mechanisms for proofreading are similar to those found in DNA polymerases.
Errors in the DNA sequence can be harmful, but they are usually short-lived.
The final stage is called Termination.
After the AAUAAA is transcribed, longation continues for a short time.
The DNA template is cut free at this point.
The pre-RNA strand is altered before it is sent out of the nucleus to the ribosome.
The details are here.
A modified guanine nucleotide is added to the 5' end.
The cap helps bind the strand to the ribosome.
A poly (A) tail is added to the 3' end.
The tail protects the strand from degradation and facilitates the release of the strand from the nucleus.
Small nuclear ribonucleoproteins, or snRNPs, are used to remove the noncoding regions of the mRNA.
Only exons, which are expressed, can leave the nucleus.
The length of the mRNA that leaves the nucleus is shorter than the original unit.
The primary transcript is the same length as the average length of the human DNA molecule that is transcribed.
An average-size protein of 200 amino acids requires only 1,200 nucleotides of RNA to code.
Out of the original 27,000 nucleotides, 15,800 are noncoding.
Scientists were expecting to find 100,000 genes before the Human Genome Project was done.
They discovered that humans only have about 22,000 genes.
It can be explained when you know the mechanism of alternative RNA splicing.
Depending on which segments of the primary transcript are treated as exons or introns, differentRNA molecules are produced from the same primary transcript.
Cell type control intron-exon choices by binding to regulatory sequences within the primary transcript.
The process by which the codons of an mRNA sequence are changed into an sequenc e is called translation.
A with U and C with G are the base pairs for the ribosome and the cytoplasm.
One end of the molecule has a specific amino acid and the other has a triplet called an anticodon.
Unlike mRNA, which is broken down immediately after being used, tRNA is used repeatedly.
The energy for this process is provided by a molecule called GTP.
The correct tRNA is joined to the correct amino acid by a specific enzyme.
There are only 20 different tRNAs.
Sixty-one of the codons code for amino acids.
One codon, AUG, has two functions; one is a start codon and the other is a code for the amino acid methionine.
Three codons, UAA, UGA, and UAG, are stop codons.
There are anticodons that can recognize two or more different codons.
The rules for the third base of a codon are not as strict as those for the first two bases.
Wobble is a relaxation of base pairs rules.
When the ribosome is attached to the mRNA, initiation begins.
The first codon is always August.
It needs to be positioned correctly in order for it to be transcribed.
A polypeptide chain is formed when the ribosome is brought into being with the help of tRNA.
Several ribosomes in clusters translate one mRNA molecule at the same time.
When a ribosome reaches one of three ends, the strand is terminated.
The ribosome is broken down after the polypeptide is freed.
The complete genetic code is shown.
There are 64 possible combinations of the nitrogenous bases.
The initiation signal for translation is AUG, which codes for methionine.
Three of the codons are stop codons.
There is no ambiguity about the genetic code.
Look at the chart.
There is more than one codon for leucine.
There is no confusion.
This code is universal and unified all life.
It shows that the code originated early in the evolution of life on Earth and that all living things descended from those first ancestral cells.
There are permanent changes in genetic material.
Toxic chemicals and radiation can cause them.
Normal cell functions are disrupted by amutation in body cells.
The genes of a population can be changed by the transmission of gametes.
Natural selection depends on the raw material.
Some parts of the genome are more vulnerable to change than others.
The regions of Cs and Gs are more strongly connected by a triple hydrogen bond than the regions of As and Ts.
The simplest thing to do is a point.
A base-pair substitution is a chemical change in one base pair.
The processing of genetic information is not perfect.
A single point deletion in a single base pair in the gene that codes for hemoglobin leads to the inherited genetic disorder.
Red blood cells can be affected by low oxygen when this point is involved.
A variety of tissues may be deprived of oxygen when red blood cells are abnormal.
There is a chance that a point change could result in a beneficial change for an organisms, because of the wobble in the genetic code.
The silent mutation shown above does not result in a change in the amino acid sequence.
A deletion is the loss of one letter, and an insert is the addition of a letter into the sentence.
The entire reading frame is altered because of the two mutations.
Changes in geno can lead to changes in phenotype.
One of two things can happen as a result of the frameshift.
Either a mutated polypeptide is formed or not.
Knowledge of genetics has been based on work with the simplest biological systems since the early part of the twentieth century.
The understanding of replication, transcription, and translation of DNA was worked out usingbacteria as a model.
The basis for how diseases are treated and how vaccines are developed is their understanding of how viruses andbacteria are transmitted.
A worldwide industry of genetic engineering and recombinant DNA relies onbacteria like Escherichia coli and viruses for research and therapeutic endeavors.
Thomas Hunt Morgan depended on the fruit fly while Gregor Mendel depended on the garden pea.
A virus can only live inside another cell.
The host cell machinery is taken over by it and used to fashion new viruses.
Thousands of new viruses are formed and the host cell is often destroyed in the process.
A capsid is a part of a virus.
The viral envelope that some viruses have is derived from the cells of the host, and aids the virus in infecting the host.
Each type of virus can only enter a cell by binding to a specific part of the cell surface.
The virus that causes colds in humans only affects the respiratory system, while the one that causes AIDS only affects one type of white blood cell.
The range of organisms that a virus can attack is referred to as the host range.
A sudden emergence of a new viral disease that affects humans, such as AIDS or H1N1, may be the result of a bug that expands its host range.
Bacteriophages are viruses that cause infections.
The viruses are complex and best understood.
There are two ways in which the bacteriophage can reproduce.
In the lytic cycle, the phage enters a host cell, takes control of the cell machinery, and then causes the cell to burst, releasing a new generation of infectious phage viruses.
The viruses kill thousands of cells in the same way.
A phage only replicates by a lytic cycle.
Viruses do not destroy the host cell in the lysogenic cycle.
The host's genes are changed by the phage virus.
It is called a prophage because it is not active within the host genome.
As the host cell divides, the phage is replicated along with it and a single cell gives rise to a population of infections.
The prophage will switch to thelytic phase at some point.
There are Viruses capable of reproducing, lytic and lysogenic within a bacterium.
Genetic variation can be introduced by viral replication.
RETROVIRUSES are viruses that have a different way of replicating.
The retrovirusesRNA is a template for the synthesis of cDNA because it is similar to theRNA from which it was copied.
The retroviruses reverse the normal flow of information.
Under the direction of the reverse transcriptase, this reverse transcription occurs.
A prophage is when a retroviruses inserts itself into the host genome and becomes a permanent resident.
HIV is an example of a retroviruses.
The phage viruses acquire bits of bacterial DNA as they invade one cell after another.
The process that leads to genetic recombination is called transduction.
There are two types of transduction: generalized and restricted.
The phage lyses one cell and lyses another during the lytic cycle as Generalized transduction moves random pieces of bacterial DNA.
The transfer of specific pieces of DNA is called restricted transduction.
A phage integrates into the host cell at a specific site during the lysogenic cycle.
When the phage breaks out of the host, it sometimes carries a piece of adjacent host DNA with it and inserts it into the next host.
The reproductive cycles of viruses transfer genetic information.
The bacterium's double-stranded DNA molecule is tightly compressed into a structure with a small amount of protein.
It is located in a region that does not have a nuclear device.
There is a single point of origin for the genes ofbacteria.
The main mode of reproduction forbacteria is asexual, which can be accomplished by using a primitive sexual method called conjugate.
In a population with all the same genes, there are no defects.
The population as a whole can vary depending on the number of copies of a single bacterium.
Eukaryotes have multiple, linear chromosomes while prokaryotes have circular chromosomes.
Frederick Griffith discovered a new strain of the bacterium Diplococcus pneumoniae in 1928.
The process of transformation can be either natural or artificial.
A stable genetic change in the recipient cell can be achieved by small pieces of extracellular DNA being taken up by a living bacterium.
Today, it is very easy to transformbacteria.
A plasmid is a foreign, small, circular, self-replicating DNA molecule.
The genes carried by the plasmid can be expressed by a bacterium.
The genes may give the bacterium an advantage.
The F plasmid was the first to be discovered.
F stands for fertility.
Those that do not carry the plasmid are called F - and those that do contain the F plasmid are called F +.
The F plasmid contains genes for the production of pili, a type of sexual reproduction that involves the transfer of DNA from one cell to another.
The R plasmid makes a cell that is resistant to specific antibiotics.
The R plasmid can be transferred to otherbacteria.
bacteria that carry the R plasmid have an advantage overbacteria that are not resistant to antibiotics The populations of resistantbacteria will increase while non resistantbacteria die out.
This is happening right now as an increasing number of populations ofbacteria are becoming resistant to antibiotics.
This is cause for concern in the health community.
Jacob and Monod discovered the operon in the 1940s.
It is an important model of gene regulation.
An operon is a set of genes and switches that control their expression.
There are two types of operons, the repressible and the inducible.
The operon is a perfect example of a free-response question about regulation.
The tryptophan operon consists of a promoter and five adjacent structural genes that are required for the synthesis of the amino acid tryptophan.
One strand of mRNA containing start and stop codons is transcribed if the promoter is binding to the RNA polymerase.
If adequate tryptophan is present, it acts as a corepressor.
The promoter is prevented from binding to the operator by the activated repressor.
There is no transcription if there is no RNA polymerase attached to the promoter.
If the repressor is activated, the tryptophan operon is always switched on.
In order for the E. coli to use lactose as an energy source, three enzymes must be synthesised.
Three genes in the lac operon are used to code for the b-galactosidase, permease, and transacetylase.
In order for the three genes to be transcribed, the repressor must be prevented from binding to the operator and the RNA polymerase must bind to the promoter region.
The inducer that facilitates this process is allolactose.
Allolactose, the inducer, can be found when a person drinks milk.
Lac can be utilized as an energy source when the lac genes are transcribed.
The E. coli preferentially metabolizes glucose when it is present in the intestine.
Lactose is an energy source for E. coli when it is in short supply.
The ability is dependent on the interaction of CAP and cAMP.
Positive gene regulation is an example of this mechanism because the attachment of CAP to the promoter directly stimulates gene expression.
A new RNA chain can be created by linking ribonucleotides to nucleotides on a DNA template.
There is a sequence of nucleotides near the start of an operon.
The binding of the repressor prevents the operon's genes from being transcribed.
The promoter is a sequence in the DNA of a gene that is the binding site of the RNA polymerase.
Repressor is aProtein that suppresses gene transcription.
The operator is bound to the repressors in the operon.
The regulators genes codes for a repressor.
It is close to the operon and has its own promoter.
Prions are neither cells nor viruses.
They are misfolded versions of the same thing.
If prions get into a normal brain, they cause all the normal versions of theProtein to misfold in the same way.
There are several brain diseases caused by prions, including scrapie in sheep, mad cow disease in cattle, and Creutzfeldt-Jakob disease in humans.
All known prion diseases are fatal.
There are 3 billion base pairs of DNA in the human genome.
Only 1% of our genes get translated into proteins.
The new research shows that a lot of the nongene DNA gets transcribed intoRNA and that there are regulatory and repetitive sequences that alter the expression of genes.
Huntington's disease is caused by long stretches of tandem repeats within affected genes.
The telomeres are made up of many tandem repeats.
Scientists have identified certain noncoding regions of DNA that are variable from one region to the next.
There is one example.
The number of repeats can vary from site to site.
There can be as many as several hundred thousand repeats of the GTTAC at one site but only a small amount in another.
This individual variation from one person to another allows forensic scientists to create a person's genetic or DNA profile, which has been used to prosecute many individuals and is the basis of several television shows.
More than 350 wrongly convicted people have been freed from prison by using the same genetic profiles.
The innocence project was founded in 1992 by Peter Neufeld and Barry Scheck at Cardozo School of Law.
The operon is an excellent model for the regulation of genes.
Although every cell in your body contains the same 3 billion base pairs of DNA, a typical cell only expresses a small percentage of its genes at any one time.
Different mechanisms regulate the expression of genes.
The mechanisms are described below.
There are places where the expression of genes can be altered.
It is possible to describe the connection between the regulation of gene expression and observable differences within cells and between individuals in a population.
The basic unit of the nucleosome is the histones, which are packaged with Eukaryotic DNA.
Changes to the histone structure make it less accessible for transcription and expression.
The inhibition can be reversed.
Adding acetyl groups to histone tails helps loosen the structure of the chromatin.
There are acetyl groups that block transcription.
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