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Protein Synthesis and Mutation (Protein Synthesis (The central dogma…
Protein Synthesis and Mutation
Protein Synthesis
The central dogma of molecular biology describes the fundamental process that makes us all different.
We all have the same genes and proteins.
We have different alleles of those genes.
The polymers that comprise DNA, RNA and amino acids are linear polymers.
The polymer's (DNA or RNA) sequence is used as a template for the construction of another polymer with a sequence that is entirely dependent on the original polymer's sequence.
The central dogma classes these into three groups of three
three special transfers
three unknown transfers
Three general transfers
Reverse transcription is the transfer of information from RNA to DNA. The is the reverse of normal transcription. Reverse transcription occurs in retroviruses, such as HIV, the virus that causes AIDS.
Reverse transcription also occurs with retrotransposons and during telomere synthesis in eukaryotes.
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.
Telomere is a region of repetitive noncoding nucleotide sequences at each end of a chromosome.
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.
RNA replication is the copying of one RNA to another.
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.
Antisense RNA molecule is a single-stranded RNA that is complementary to a mRNA strand transcribed within a cell.
The Sequence of Steps in the Transcription Process:
Initiation - Elongation - Termination
Transcription uses a DNA template to make a strand of mRNA in the nucleus.
Transcription
RNA-Polymerse III synthesizes tRNAs
RNA-Polymerse II synthesizes mRNAs and most snRNAs and microRNAs.
Genetic Code
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.
Each codon stands for (encodes) one amino acid, unless it codes for a start or stop signal.
There are 64 possible codons, more than enough to code for the 20 amino acids.
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.
This codon is also the start codon that begins translation.
Characteristics of the 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.
The genetic code is unambiguous. Each codon codes for just one amino acid (or start or stop). What might happen if codons encoded more than one amino acid?
The genetic code is redundant. Most amino acids are encoded by more than one codon.
The genetic code is universal, unambiguous, and redundant.
The codons are read in sequence following the start codon until a stop codon is reached.
The genetic code consists of the sequence of bases in DNA or RNA.
Groups of three bases form codons, and each codon stands for one amino acid (or start or stop).
Translation
Transfer RNAs or tRNAs bring or tansfer the proper amino acid to the ribosome based on the genetic code
The anticodon at the bottom of the tRNA molecule binds to the codon on the mRNA.
The mRNA moves from the nucleus to the cytoplasm to interact with a ribosome, which serves as the site of translation. Translation proceeds in three phases: initiation, elongation and termination
mRNA, rRNA, and tRNA all work together to complete the process of translation
Translation is the process of ordering the amino acids into a polypeptide; translation involves changing the language of nucleotides into the language of amino acids.
The covalent attachment of an amino acid to the tRNA is catalyzed by enzymes called aminoacyl-tRNA syntheses through a process called aminoacylation.
After the protein is made, it must fold into its functional conformation.
Translation involves the interactions of the three types of RNA: mRNA, rRNA and tRNA.
Initiation of Eukaryotes
The initiation of translation in prokaryotes involves the assembly of the ribosome and addition of the first amino acid, methionine. The 30S ribosomal subunit attaches to the mRNA.