Please enable JavaScript.
Coggle requires JavaScript to display documents.
Protein Synthesis and Mutation (Transcription (Transcription takes place…
Protein Synthesis and Mutation
Transcription
The process in which cells make proteins is called protein synthesis. It actually consists of two processes:
transcription
and translation.
Transcription takes place in the nucleus. It uses DNA as a template to make an RNA molecule.
Transcription: first part of the central dogma of molecular biology: DNA → RNA. Transfer of genetic instructions in DNA to messenger RNA (mRNA). During transcription, a strand of mRNA is made that is complementary to a strand of DNA.
Transcription takes place in three steps: initiation, elongation, and termination
Initiation~
is the beginning of transcription. It occurs when the enzyme RNA polymerase binds to a region of a gene called the promoter. This signals the DNA to unwind so the enzyme can ‘‘read’’ the bases in one of the DNA strands. The enzyme is now ready to make a strand of mRNA with a complementary sequence of bases.
Elongation+
is the addition of nucleotides to the mRNA strand. RNA polymerase reads the unwound DNA strand and builds the mRNA molecule, using complementary base pairs.
Termination X
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.
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.
letters are combined in groups of three to form code “words,” called
codons
. Each codon stands for (encodes) one amino acid, stop/start signal
Reading GC
AUG codes for the amino acid methionine;
start codon
that begins translation
The start codon establishes the reading frame of mRNA. The
reading frame
is the way the letters are divided into codons.
The mRNA molecule is read, codon by codon, until a
stop/termination codon
is reached. Ex) UAG, UGA, and UAA
Translation
second part of the central dogma of molecular biology: RNA → Protein.
process in which the genetic code in mRNA is read, one codon at a time, to make a protein.
After mRNA leaves the nucleus, it moves to a ribosome, which consists of rRNA and proteins. The ribosome reads the sequence of codons in mRNA. Molecules of
tRNA
bring amino acids to the ribosome in the correct sequence.
Each tRNA molecule has an anticodon. An anticodon-sequence of 3 bases; complementary to the codon for an amino acid. Ex) AAG=UUC
Bonds form between adjacent amino acids as they are brought to the ribosome, forming a
polypeptide chain.
Mutations
A change in sequence of bases in DNA or RNA
Frameshift Mutation
deletion or insertion of one or more nucleotides that changes the reading frame of the base sequence.
Germline Mutations
occur in gametes; can be transmitted to offspring and every cell in the offspring will have the mutation.
Somatic Mutations
occur in other cells of the body; may have little effect on the organism because they are confined to just one cell and its daughter cells; cannot be passed on to offspring.
Chromosomal alterations
-change chromosome structure. They occur when a section of a chromosome breaks off and rejoins incorrectly or does not rejoin at all
Deletion, Duplication, Inversion, Insertion, Translocation
Point Mutation-change in a single nucleotide in DNA
Missense
-mutated codon codes for a different amino acid CAA (glutamine) → CCA (proline)
Nonsense
-mutated codon is a premature stop codon CAA (glutamine) → UAA (stop
Silent
-mutated codon codes for the same amino acid Ex)CAA (glutamine) → CAG (glutamine)