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Protein Synthesis and Mutations (Genetic Code (The genetic code is…
Protein Synthesis and Mutations
Protein Synthesis
The two processes necessary to make a protein from the information in DNA are transcription and translation.
The central dogma of molecular biology describes the fundamental process that makes us all different. DNA → RNA → Protein
Transcription, which happens in the nucleus, uses the DNA sequence to make an RNA molecule. The RNA then leaves the nucleus and goes to the cytoplasm where translation occurs on a ribosome and produces a protein. [RNA polymerase is involved]
Our proteins are slightly different because we have different alleles. They are our particle version of the genetic instructions. It is those small difference in the DNA sequence of different alleles that is translated into small differences in the mRNA molecules.
Splicing removes introns from mRNA.
The regions in mRNA that do not code for proteins are called introns.
The regions of mRNA that code for proteins are called exons.
mRNA may be modified before it leaves the nucleus by splicing, editing, and polyadenylation.
RNA leaves the nucleus and goes to the cytoplasm where translation occurs on a ribosome.
Reverse transcription is the transfer of information from RNA to DNA.
Retroviruses are RNA viruses that are duplicated in a host cell by using reverse transcriptase enzyme to produce DNA from its RNA genome.
Transcription
An antisense RNA molecule is a single-stranded RNA that is complementary to a mRNA strand transcribed within a cell. These two RNAs bind to each other and prevent translation. RNA interference is a form of gene silencing.
RNA silencing refers to mechanisms of gene silencing, in which the expression of one or more genes is downregulated or entirely suppressed by the binding of an antisense RNA molecule.
Retrotransposons are self-replicating segments of eukaryotic genomes that use reverse transcriptase to move from one position in the genome to another via a RNA intermediate.
Telomerase is a reverse transcriptase that uses an RNA intermediate to elongate the 3' end of DNA strands in the telomere regions after each replication cycle.
A telomere is a region of repetitive noncoding nucleotide sequences at each end of a chromosome.
Retrotransposons are self-replicating segments of eukaryotic genomes that use reverse transcriptase to move from one position in the genome to another via a RNA intermediate.
Retroviruses are RNA viruses that are duplicated in a host cell by using reverse transcriptase enzyme to produce DNA from its RNA genome.
With three biopolymers (DNA, RNA, and protein), there could be as many as nine potential types of transfers. The central dogma classes these into three groups of three: three special transfers, three general transfers, three unknown transfers.
The three general transfers are believed to occur normally in most cells. These describe the normal flow of biological information. DNA is replicated, DNA is transcribed into RNA, and RNA is translated into protein. The three special transfers are known to occur under special conditions, such as with some viruses. The three unknown transfers are not believed to occur.
Termination of transcription involves the detachment of the RNA from the DNA template.
In Rho-independent termination, RNA transcription stops when the newly synthesized RNA molecule forms a hair-pin loop followed by a run of uracils.
Genetic Code
The genetic code is universal. All known living organisms use the same genetic code. This shows that all organisms share a common evolutionary history.
There are 20 common amino acids in proteins. There are 64 possible codons, more than enough to code for the 20 amino acids.
the codon AUG codes for the amino acid methionine. This codon is also the start codon that begins translation.
Each codon stands for (encodes) one amino acid, unless it codes for a start or stop signal.
The genetic code is unambiguous. Each codon codes for just one amino acid (or start or stop).
The genetic code consists of the sequence of nitrogen bases—A, C, G, U—in an mRNA chain. The four bases make up the “letters” of the genetic code. The letters are combined in groups of three to form code “words,” called codons.
The genetic code is redundant. Most amino acids are encoded by more than one codon.
The start codon establishes the reading frame of mRNA. The reading frame is the way the letters are divided into codons. After the AUG start codon, the next three letters are read as the second codon and so on...
The mRNA molecule is read, codon by codon, until a stop codon is reached. UAG, UGA, and UAA are all stop codons. They do not code for any amino acids. Stop codons are also known as termination codons.
Redundancy in genetic code protects against mutations.
The Wobble Hypothesis states that rules of base pairing are relaxed at the third position, so that a base can pair with more than one complementary base.
The reading frame is the frame of three bases in which the mRNA is read and translated.
The genetic code is used as a language to produce a specific polypeptide chain.
Translation always begins with an AUG start codon. 2. The start codon establishes the reading frame of mRNA. 3. The mRNA molecule is read one codon at a time until a stop codon is reached.
Mutations
n the hominids that arose after the split from the orangutans, two chromosomes fused to produce what is chromosome 2 in humans.
More than a million copies of the Alu sequence are present in the human genome, making this transposon equivalent to just under 11% of the human genome.
Genetic recombination after duplication of different domains forms new combinations of domains with new functions.
DNA sequences that can translocate around the genome comprise a significant fraction of the genetic material of plants and animals. There may be some evolutionary significance to these movable elements. One example is the Alu sequence or Alu element.
A mutation is a change in the DNA or RNA sequence, and many mutations result in new alleles.
Alu elements are about 300 base pairs long and are classified as short interspersed elements (SINEs) among the class of repetitive DNA elements. It is believed modern Alu elements evolved from a head to tail fusion of two distinct antique RNA monomers over 100 million years ago. The monomers are opposing but complementary RNA fragments joined by an A-rich linker. Alu elements are derived from the signal recognition particle RNA.
This RNA is the RNA component of the signal recognition particle (SRP) ribonucleoprotein complex. This complex is a universally conserved ribonucleoprotein that directs the traffic of proteins within the cell and allows them to be secreted.
Causes of Mutation
Mutagenesis is a process by which the genetic information of an organism is changed in a stable manner, resulting in a mutation. In nature mutagenesis can lead to changes that are beneficial or harmful, or have no effect.
A spontaneous mutation can just happen. These mutations are not caused by an environmental factor, but occur during normal cellular processes. A spontaneous mutation may be due to a mistake during DNA replication or transcription. Mutations may also occur during mitosis and meiosis.
A mutation caused by an environmental factor, or mutagen, is known as an induced mutation.
The majority of mutations have neither negative nor positive effects on the organism in which they occur. These mutations are called neutral mutations.
Typical mutagens include chemicals, like those inhaled while smoking, and radiation, such as X-rays, ultraviolet light, and nuclear radiation.
Some mutations have a positive effect on the organism in which they occur. They are called beneficial mutations. They lead to new versions of proteins that help organisms adapt to changes in their environment. Beneficial mutations are essential for evolution to occur. They increase an organism’s changes of surviving or reproducing, so they are likely to become more common over time.
Some mutations have a positive effect on the organism in which they occur. They are called beneficial mutations. They lead to new versions of proteins that help organisms adapt to changes in their environment. Beneficial mutations are essential for evolution to occur. They increase an organism’s changes of surviving or reproducing, so they are likely to become more common over time.