Protein synthesis Flashcards
Unit 4 (21 cards)
What is a polypeptide chain?
Amino acids bond by peptide bonds to form long polypeptide chains.
What is a triplet code?
Every 3 bases in a gene codes for 1 amino acids and there are 64 different codes so some amino acids have more than one code.
What do stop codons do?
mark the end of the sequence
What are exons?
Sections of DNA that code for amino acids.
What are introns?
sections of DNA that don’t code for one amino acid and are found between and in genes.
What is a degenerate code?
More than one codon can code for one amino acid, the code is non-overlapping and universal.
How would a change in one result in an enzyme becoming non-functional?
Change in sequence of amino acids, which changes ionic bonds when chain folds. This changes the tertiary structure and changes the shape of the active site making it no longer complementary to substrate so no enzyme-substrate complexes form.
Describe the structure of RNA
A polymer made up of mononucleotide subunits to form a single strand and is one of the organic bases (adenine, guanine, cytosine, uracil)
What are the three different types of RNA?
- ribosomal RNA
- messenger RNA (mRNA)
- transfer RNA (tRNA)
What is a codon?
The sequence of three bases on mRNA that codes for a single amino acid.
What is a genome?
The complete set of genes in a cell, including those in the mitochondria and/or chloroplasts.
What is a proteome?
The full range of proteins produced by a genome.
How is the information coded for by DNA transferred from the nucleus to the cytoplasm?
Sections of the DNA code are transcribed onto single-stranded mRNA.
Describe the structure of mRNA
- consists of thousands of mononucleotides
- long strand arranged in a single helix
- base sequence is determined by transcription
- mRNA is small enough to leave the nucleus vis the nuclear pores and enters the cytoplasm
Describe the function of mRNA
- associates with the ribosomes where its acts as a template for protein synthesis
- structure allows for this as it carries the genetic information in the form of codons
- sequence of codons determines the amino acid sequence of the specific polypeptide that will be made
Describe the structure of tRNA
- relatively small molecule made up of around 80 nucleotides
- single stranded chain folded into a clover shape
What replaces thymine in RNA?
Uracil
What is transcription?
A complementary copy of a single gene is made. DNA helicase breaks H bonds and separates the DNA strands. One strand acts as a template and free RNA nucleotides complementary base pair to the exposed bases on this strand. Uracil binds to adenine rather than thymine. RNA polymerase forms phosphodiester bonds between adjacent RNA nucleotides by condensation reactions and build it in a 5’ to 3’ direction. The new RNA strand detaches from the template strand, the two DNA strands join together by complementary base pairing, the new RNA strand is called pre-mRNA.
What is the problem with pre-mRNA?
Introns within the coding sequences, these need removing before it can be used to sequence the amino acids at the ribosome.
What is splicing?
Specific enzymes cleave the pre-mRNA at specific points to remove the introns. Once removed, exons join back to form mature-mRNA. This means it can now leave the nucleus to move to the ribosome for translation.
What is translation?
The sequence of bases in mRNA is translated into a sequence of amino acids at the ribosomes. The first two codons of mRNA attach to the ribosome. Molecules of tRNA have anticodons of a specific 3 base sequence. In the cytoplasm there will be some tRNA molecules that have anticodons that are complementary to the mRNA codons attached to the ribosome. tRNA with an anticodon complementary to the first mRNA codon base pairs with it forming H bonds. This brings the first amino acid (Met) to the ribosome. tRNA with an anticodon complementary to the 2nd mRNA codon base pairs with it, forming H bonds, this brings the 2nd amino acid to the ribosome. An enzyme, plus energy from ATP hydrolysis, catalyzes the formation of a peptide bond between the first 2 amino acids. The ribosome moves the mRNA along to bind to the 3rd codon. The first tRNA detaches, leaving behind its specific amino acid. tRNA molecule with anticodon complementary to the 3rd mRNA codon base pairs with it. This brings another specific amino acid. Peptide bonds form and the ribosome moves the mRNA along by one more codon and this process continues… The last codon on mRNA does not have a complementary tRNA anticodon. No further amino acids are added on. The polypeptide chain is complete.
