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BIO CH 16 (DNA replication (both strands (Once all of the bases are…
BIO CH 16
DNA replication
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lagging strand
Chunks of DNA, called Okazaki fragments, are then added to the lagging strand also in the 5’ to 3’ direction.
Numerous RNA primers are made by the primase enzyme and bind at various points along the lagging strand.
This type of replication is called discontinuous as the Okazaki fragments will need to be joined up later.
leading strand
A short piece of RNA ?called a primer? (produced by an enzyme called primase) comes along and binds to the end of the leading strand.
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DNA polymerase binds to the leading strand and then ‘walks’ along it, adding new complementary- nucleotide?
bases (A, C, G and T) to the strand of DNA in the 5’ to 3’ direction.
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both strands
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Finally, an enzyme called DNA ligase? seals up the sequence of DNA into two continuous double strands.
Once all of the bases are matched up (A with T, C with G), an enzyme called exonuclease strips away the primer(s)
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The result of DNA replication is two DNA molecules consisting of one new and one old chain of nucleotides.
This is why DNA replication is described as semi-conservative, half of the chain is part of the original DNA molecule, half is brand new.
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DNA structure
is made up of molecules called nucleotides. Each nucleotide contains a phosphate group, a sugar group and a nitrogen base.
The four types of nitrogen bases are adenine (A), thymine (T), guanine (G) and cytosine (C). The order of these bases is what determines DNA's instructions, or genetic code
distributed among 46 long structures called chromosomes. These chromosomes are made up of thousands of shorter segments of DNA, called genes.
is a molecule composed of two polynucleotide chains that coil around each other to form a double helix carrying genetic instructions
for the development, functioning, growth and reproduction of all known organisms and many viruses.
The nucleotides of DNA consist of a deoxyribose sugar molecule to which is attached a phosphate group
The two DNA strands are known as polynucleotides as they are composed of simpler monomeric units called nucleotides.
The nucleotides are joined to one another in a chain by covalent bonds (known as the phospho-diester linkage)
between the sugar of one nucleotide and the phosphate of the next, resulting in an alternating sugar-phosphate backbone.
The nitrogenous bases of the two separate polynucleotide strands are bound together, according to base pairing rules (A with T and C with G)
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Each nucleotide is composed of one of four nitrogen-containing nucleobases (cytosine [C], guanine [G], adenine [A] or thymine [T]), a sugar called deoxyribose, and a phosphate group.
The complementary nitrogenous bases are divided into two groups, pyrimidines and purines.
In DNA, the pyrimidines are thymine and cytosine; the purines are adenine and guanine.
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non-coding, meaning that these sections do not serve as patterns for protein sequences.
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The nucleotides are joined together by covalent bonds between the phosphate of one nucleotide and the sugar of the next
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the sequencing of this bonding is specific—i.e., adenine bonds only with thymine, and cytosine only with guanine
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telomeres
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importance
to be protected from a cell's DNA repair systems because they have single-stranded overhangs, which "look like" damaged DNA.
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prevent the loss of genes as chromosome ends wear down, the tips of eukaryotic chromosomes have specialized DNA “caps”
They also protect genetic information during cell division because a short piece of each chromosome is lost every time DNA is replicated.
Cells use a special enzyme called telomerase to keep dividing, which lengthens their telomeres
During chromosome replication, the enzymes that duplicate DNA cannot continue their duplication all the way to the end of a chromosome, so in each duplication the end of the chromosome is shortened
he telomeres themselves are protected by a complex of shelterin proteins, as well as by the RNA that telomeric DNA encodes
The telomeres are disposable buffers at the ends of chromosomes which are truncated during cell division; their presence protects the genes before them on the chromosome from being truncated instead.
Over time, due to each cell division, the telomere ends become shorter.[7] They are replenished by an enzyme, telomerase reverse transcriptase
tellers facts
Most prokaryotes, having circular chromosomes rather than linear, do not have telomeres.
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A protein complex known as shelterin serves to protect the ends of telomeres from being recognised as double-strand breaks by inhibiting homologous recombination
Telomeres are repetitive nucleotide sequences located at the termini of linear chromosomes of most eukaryotic organisms.
For vertebrates, the sequence of nucleotides in telomeres is TTAGGG
The known structures of bacterial telomeres take the form of proteins bound to the ends of linear chromosomes, or hairpin loops of single-stranded DNA at the ends of the linear chromosomes
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DNA mutation
A mutation is a change in DNA, the hereditary material of life. Mutations are essential to evolution; they are the raw material of genetic variation.
An organism's DNA affects how it looks, how it behaves, and its physiology. So a change in an organism's DNA can cause changes in all aspects of its life.
a mutation is an alteration in the nucleotide sequence of the genome of an organism, virus, or extrachromosomal DNA.
cause of mutation
radiation
Gamma rays, X-rays, even UV light can interact with compounds in the cell generating free radicals which cause chemical damage to DNA.
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Chemical Damage to DNA
chemical mutagens, some exogenous, some man-made, some environmental, are capable of damaging DNA. Many chemotherapeutic drugs and intercalating agent drugs function by damaging DNA.
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types of mutations
Substitution
A substitution is a mutation that exchanges one base for another (i.e., a change in a single "chemical letter" such as switching an A to a G)
Insertion
Insertions are mutations in which extra base pairs are inserted into a new place in the DNA.
Deletion
Deletions are mutations in which a section of DNA is lost, or deleted.
Frameshift
Since protein-coding DNA is divided into codons three bases long, insertions and deletions can alter a gene so that its message is no longer correctly parsed. These changes are called frameshifts.
In frameshifts, a similar error occurs at the DNA level, causing the codons to be parsed incorrectly.
effects of mutation
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Small change occurs in phenotype.
A single mutation caused this cat's ears to curl backwards slightly.
No change occurs in phenotype.
Some mutations don't have any noticeable effect on the phenotype of an organism.
This can happen in many situations: perhaps the mutation occurs in a stretch of DNA with no function, or perhaps the mutation occurs in a protein-coding region
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Big change occurs in phenotype.
Some really important phenotypic changes, like DDT resistance in insects are sometimes caused by single mutations.
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Mutations that cause the death of an organism are called lethals — and it doesn't get more negative than that.