Unit 4,protein synthesis Flashcards
characteristics of mRNA
-made during transcription
-carries genetic code from DNA to ribosome eventually making a protein, because dna is to large to move to dna
-they are a single polynucleotide strand
characteristics of tRNA
-involved in translation
-carries the amino acids that are used to make proteins to the ribosomes
-single polynucleotide strand that is folded into a clover shape, held in shape by hydrogen bonds
-at one end there is a specific anticodon that binds to mRNA
-at the other end has an amino acid binding site
what is the 1st stage of the transcription process?
RNA polymerase attaches to DNA
-transcription starts when RNA polymerase attaches at the start of a gene. when the DNA is unwound by the helicase the remainder strand of the DNA is used as a template to make a mRNA copy
- helicase breaks hydrogen bonds
what is the 2nd stage of the transcription process?
Complementary mRNA is formed
-RNA polymerase lines up and joins complementary bases to form mRNA for a complementary copy
what is the 3rd stage of the transcription process?
RNA polymerase moves down DNA strand
-RNA polymerase forms hydrogen bonds as the double helix reforms
what is the 4th stage of the transcription process?
RNA polymerase reaches stop signal
- meets a particular sequence called a stop signal, so it stops making mRNA and detaches from the DNA
-in eukaryotes it moves out of the nucleus through nuclear pores and attaches to ribosomes in the cytoplasm
what happens in editing of mRNA in eukaryotes?
-introns and exons that are copied into mRNA are called pre-mRNA
-splicing then occurs
what is splicing?
-introns are removed and exons are joined together forming an mRNA strand, which leaves the nucleus for translation, introns removed by splicesome
- exons can re-join together in a variety of combinations, so multiple proteins are made
what happens in the editing of mRNA in prokaryotes?
there are no introns in prokaryotes DNA, so mRNA is made directly from the DNA
what happens if a mutation occurs in editing of mRNA that alters pre-mRNA?
can lead to non functional polypeptides, for example Alzheimer’s
what are exons?
regions which code for protein
what are introns?
regions which do NOT code for proteins
Where does translation take place?
In the ribosome
What is a proteome?
Entire complement of proteins that can be expressed from genes
What is the first stage of translation?
The mRNA attaches itself to a ribosome and tRNA molecules carry amino acids to it. ATP provides energy for this bond.
What is the second stage of translation?
A tRNA molecule that’s carrying an amino acid that has a complementary anticodon to the first codon of the mRNA attaches together. A second tRNA molecule repeats this. Catalysed by an enzyme and ATP
What is the third stage of translation?
The two amino acids that are attached to the tRNA are joined by a peptide bond. The first tRNA moves away and leaves the amino acid behind.
What is the fourth stage of translation?
The third tRNA molecule binds to the next codon on the mRNA, they are complementary. The amino acid joins to the previous two by a peptide bond. The second tRNA molecule moves away
What is the fifth stage of translation?
The process continues for a formation of amino acids in a chain, until the stop signal is reached. The polypeptide chain moves away from ribosome.
What amino acid always is involved in the first stage?
Methionine
What does degenerate mean?
Each amino acid could be coded for more than one amino acid ( the triplet code)
