DNA and protein synthesis Flashcards
What is the process of transcription?
Transcription is the process of making pre mRNA using the DNA as a template.
The double strands of DNA are separated by helicase, which breaks the hydrogen bonds between bases.
The bases on the template strand pair with complementary free nucleotides. Guanine pairs with cytosine and Adenine pairs with uracil.
The enzyme RNA polymerase moves along the strand and joins the nucleotides together to make a molecule of pre mRNA.
This pre mRNA then needs to be spliced to make mRNA. Splicing involves removing sections called introns, which do not code for proteins, and then joining together the ends of the remaining sections called exons, which do code for proteins.
Splicing does not occur in prokaryotic cells because they do not have introns. Once the mRNA molecules have been spliced, they leave the nucleus via a nuclear pore, and move to the ribosomes to begin translation.
What is the process of translation?
The ribosome attaches to the start codon at one end of the mRNA molecule.
The tRNA with the complementary anticodon moves to the ribosome and pairs with the codon on the mRNA. This tRNA carries a specific amino acid. Another tRNA molecule will pair with the next codon on the mRNA, bringing another specific amino acid.
The two amino acids then join by a condensation reaction, forming a peptide bond, and requiring energy from the hydrolysis of ATP.
A third amino acid will then join, and the first tRNA will be released to collect another amino acid. The process continues until a stop codon is reached, and the polypeptide chain is released from the ribosome.
The polypeptide will then be folded into secondary and tertiary structure, and different chains along with non-protein groups could be linked to form quaternary structure.
What is mRNA?
It transfers the DNA code from the nucleus to the cytoplasm by acting as a type of messenger.
It is small enough to leave the nucleus through the nuclear pores and to enter the cytoplasm, where the coded information it contains is used to determine the sequence of amino acids in the proteins which are synthesised there.
What is a codon?
The sequence of three bases on mRNA that codes for a single amino acid.
Why must DNA be transferred?
In eukaryotic cells DNA is largely confined to the nucleus, but the synthesis of proteins takes place in the cytoplasm.
So sections of the DNA code are transcribed onto a single-stranded molecule called ribonucleic acid (RNA).
What is the genome?
The complete set of genes in a cell, including those in mitochondria or chloroplasts.
What is the proteome?
The full range of proteins produced by the genome.
It can be called the complete proteome, where the proteome refers to the proteins produced by a given type of cell under a certain set of conditions.
What is the structure of RNA?
A polymer made up of repeating mononucleotide sub-units.
It forms a single strand.
Each nucleotide is made up of:
Pentose sugar ribose.
One of the organic bases Adenine, Uracil, Guanine or Cytosine.
A phosphate group.
mRNA and tRNA are used in protein synthesis.
What is the structure of mRNA?
It consists of thousands of mononucleotides, and is a long strand arranged in a single helix.
The bases sequence is determined by the sequence of bases on a length of DNA in transcription.
There is a great variety of types.
Once formed, mRNA leaves the nucleus via pores and enters the cytoplasm, where it associates with the ribosomes.
It then acts as a template for protein synthesis.
How is mRNA structure linked to its function?
It possesses information in the form of codons, the sequence of codons determines the amino acid sequence of a specific polypeptide that will be made.
What is tRNA?
It is a relatively small molecule that is made up of 80 nucleotides.
It is a single stranded chain folded into a clover-leaf shape, with one end of the chain extending beyond the other, this is where an amino acid can easily attach.
There are about 60 different types of tRNA, each of which binds to a specific amino acid.
At the opposite end is a sequence of three other organic bases, the anticodon.
The genetic code is degenerate so there must be as many tRNA molecules as coding triplets.
Each tRNA is specific to one amino acid and has an anticodon specific.
Why are mRNA and tRNA suited for protein synthesis?
During protein synthesis, an anticodon pairs with the three complementary organic bases that make up the codon on mRNA.
The tRNA structure, with its end chains for attaching amino acids and its anticodon for complementary base pairing with the codon on the mRNA, is structurally suited to its role of lining up amino acids on the mRNA template during protein synthesis.
Why must pre-mRNA be spliced?
The DNA of a gene in eukaryotic cells is made up of sections called exons that code for proteins and sections called introns that do not.
These intervening introns would prevent the synthesis of a polypeptide in the pre-mRNA of eukaryotic cells.
Slicing of pre-mRNA produces mRNA.
What is splicing?
The base sequences corresponding to the introns are removed and the functional exons are joined together.
As most prokaryotic cells do not have introns, splicing of their DNA is unnecessary.
How does mRNA get to translation?
The mRNA molecules are too large to diffuse out of the nucleus and so, once they have been spliced, they leave via a nuclear pore.
Outside the nucleus, mRNA is attracted to the ribosomes to which it becomes attached, ready for translation.
