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Chapter 16-17 (((Primase: an enzyme that synthesizes short RNA sequences…
Chapter 16-17
Primase: an enzyme that synthesizes short RNA sequences called primers. These primers serve as a starting point for DNA synthesis.
Transformation: is a key step in DNA cloning. It occurs after restriction digest and ligation and transfers newly made plasmids to bacteria
Okazaki Fragments: are pieces of DNA that are transient components of lagging strand DNA synthesis at the replication fork.
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Origins of replication: is a sequence of DNA at which replication is initiated on a chromosome, plasmid or virus.
Antiparallel: A term applied to two molecules that are side by side but run in opposite directions. The two strands of DNA are antiparallel. The head of one strand is always laid against the tail of the other strand of DNA
Semiconservative: The replication in which one strand of DNA is conserved and the other is synthesized according to complementary base pairing is called semi-conservative replicatio
Single-strand binding proteins: It binds to ssDNA and to an array of partner proteins to recruit them to their sites of action during DNA metabolism
Topoisomerase This enzyme prevents the DNA double helix ahead of the replication fork from getting too tightly wound as the DNA is opened up
DNA Ligase: is a DNA-joining enzyme. If two pieces of DNA have matching ends, ligase can link them to form a single, unbroken molecule of DNA.
Mismatch Repair: a process that corrects mismatched nucleotides in the otherwise complementary paired DNA strands, arising from DNA replication errors and recombination, as well as from some types of base modifications.
Telomeres: are distinctive structures found at the ends of our chromosomes. They consist of the same short DNA sequence repeated over and over again.
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RNA Processing
ribonucleic acid (RNA) polymerase transcribes an RNA copy of a gene, the primary transcript.
A 5' cap is added to the beginning of the RNA transcript, and a 3' poly-A tail is added to the end.
In splicing, some sections of the RNA transcript (introns) are removed, and the remaining sections (exons) are stuck back together
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Exons: The parts that are expressed are called .They appear in short sequences scattered throughout the gene. Exons are the parts of a eukaryotic gene that are expressed through transcription and translation
Introns: are the intervening sequences that are removed from a gene before the RNA product is made. They are usually considered non-coding regions because they don't need to code for any enzymes or structural proteins.
Spliceosomes: remove introns from the genes in RNA. Spliceosomes are composed of a mixture of protein and small RNA molecules. They locate the ends of the introns, cut them away from the exons, and join the ends of adjacent exons together.
Chromatin
Chromatin: is a mass of genetic material composed of DNA and proteins that condense to form chromosomes during eukaryotic cell division. Chromatin is located in the nucleus of cells.
The primary function of chromatin is to compress the DNA into a compact unit that will be less voluminous and can fit within the nucleus.
Chromatin consists of complexes of small proteins known as histones and DNA. Histones help organize DNA into structures called nucleosomes by providing a base on which the DNA can be wrapped around.
A nucleosome consists of a DNA sequence of about 150 base pairs that is wrapped around a set of eight histones called an octamer.
Heterochromatin: The tightly packed form of DNA in the chromosome.The main function of the heterochromatin is to protect the DNA from the endonuclease damage; it is due to its compact nature. It also prevents the DNA regions to get accessed to proteins during gene expression.
Euchromatin: The loosely packed form of DNA in the chromosome. The active genes present in euchromatin gets transcribed to make mRNA whereby further encoding the functional proteins is the main function of euchromatin.
Translation is the process by which a protein is synthesized from the information contained in a molecule of messenger RNA (mRNA).
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Ribosomes bind to mRNA in the cytoplasm and move along the molecule in a 5’ – 3’ direction until it reaches a start codon
Anticodons on tRNA molecules align opposite appropriate codons according to complementary base pairing (e.g. AUG = UAC)
Ribosomes catalyse the formation of peptide bonds between adjacent amino acids (via condensation reactions)
The ribosome moves along the mRNA molecule synthesising a polypeptide chain until it reaches a stop codon
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mRNA - messenger RNA is a copy of a gene. acts as a photocopy of a gene by having a sequence complementary to one strand of the DNA and identical to the other strand. The mRNA carrIES the information stored in the DNA in the nucleus to the cytoplasm where the ribosomes can make it into protein.
tRNA - transfer RNA is a small RNA that has a very specific secondary and tertiary structure such that it can bind an amino acid at one end, and mRNA at the other end. It acts as an adaptor to carry the amino acid elements of a protein to the appropriate place as coded for by the mRNA.
rRNA - ribosomal RNA is one of the structural components of the ribosome. Its sequence is the compliment of regions in the mRNA so that the ribosome can match with and bind to an mRNA it will make a protein from.
Ribozyme: are RNA enzymes that catalyze certain biochemical reactions, such as in the aminotransferase activity of the ribosome and in the cleavage (or ligation) of its own or another RNA.
Ribozyme ccurs within the ribosome. Ribosomes are biomolecules in the cytoplasm that participate in protein synthesis.
Chromosomes
Chromosome: are composed of DNA and proteins packed tightly to form long chromatin fibers. Chromosomes house genes responsible for the inheritance of traits and guidance of life processes.
Chromosome structure consists of a long arm region and a short arm region connected at a central region known as a centromere. The ends of a chromosome are called telomeres.
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Transcription: The process of transcribing or making a copy of genetic information stored in a DNA strand into a complementary strand of RNA (messenger RNA or mRNA) with the aid of RNA polymerases
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Elongation:
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RNA polymerase reads the unwound DNA strand and builds the mRNA molecule, using complementary base pairs.
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During this process, an adenine (A) in the DNA binds to an uracil (U) in the RNA.
Termination:
Is the ending of transcription, and occurs when RNA polymerase crosses a stop (termination) sequence in the gene. The mRNA strand is complete, and it detaches from DNA.
DNA
DNA: is made up of nucleotides: 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.
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