Transcription and translation Flashcards
What is mRNAs role?
Transfers the DNA code from the nucleus to the cytoplasm through nuclear pores where it asssociates with ribosomes which act as a template for protein synthesis.
The codons are used to determine the sequence of amino acids in the polypeptide chain that is made there
Describe mRNAs structure
It consists of thousands of mononucleotides, arranged into a single helix and it possesses its information in the form of codons,
The sequence of these determines the amino acid sequence of a specific polypeptide that will be made
Describe RNAs stucture
It is a polymer made of repeating mononucleotides, each made up of the pentose sugar, one of the organic bases, and a phosphate group
What does codon mean
Sequence of 3 bases on mRNA that codes for a single amino acid
What does genome mean
The complete set of genes in a cell including those in mitochondria and cytoplasm
What does protenome mean
The full range of proteins coded for by the genome
Describe the shape of a tRNA molecule
A small molecule that is made up of around 80 nucleotides, it is a single stranded chain folded into a clover leaf shape with one end of the chain extending beyond the other and this is where the amino acid molecule attaches, then at the opposite end of the amino acid there are anticodon loops
How do the organic bases pair up in complementary base pairing in RNA
Guanine with cytosine
Adenine with uracil
What does transcription in a prokaryotic cell result in?
Results directly in the production of mrna from DNA
What does transcription in a eukaryotic cell result in?
Production of pre mrna from the DNA which is then spliced to form mrna
Describe the process of transcription
This is the process of synthesisng pre mRNA using part of the DNA as a template , –DNA helicase enzyme acts on a specific part of the DNA causing the two strands to unwind and expose the nucleotide bases in that region by breaking hydrogen bonds between complementary base pairs
The nucleotide bases on the template strand pair with complementary nucleotides from the pool in the nucleus which align with opposite exposed complementary DNA bases forming hydrogen bonds The enzyme RNA polymerase the moves along the strand and joins the nucleotides together forming phosphodiester bonds to form a pre MRNA molecule, l
What is an intron
A base sequence of DNA that does not code for proteins, these can intervene and prevent the synthesis of a polypeptide
What is an extron
A base sequence of DNA that does code for certain polypeptides
How is pre mRNA changed to form m RNA?
The base sequences corresponding to the introns are removed then the functional exons are joined together in a process called splicing
Why doesnt prokaryotic cell DNA undergo splicing?
They do not contain introns that intervene and prevent the synthesis of a polypeptide
How does translation begin?
When the mRNA molecule has been spliced so it leaves through a nuclear pore and is attracted to a ribsome where ir becomes attached
Describe the process of translation
This is the stage in which the polypeptide chain is created using both the mRNA base sequence and the tRNA. Once the mRNA has been modified and left the nucleus, it attaches to a ribosome in the cytoplasm. This ribosome will then attach to the 3 end of the mRNA at the start codon, AUG. The tRNA molecule with the complementary anticodon to the AUG codon aligns opposite the mRNA, held in place by the ribsosome. This ribosome will then move along the mRNA molecule to enable another complementary tRNA to attach to the next codon on the mRNA
The amino acids that have been delivered by the tRNA molecule are joined together by a peptide bond which is catalysed by peptidyle transferase enzyme and ATP which is hydrolysed to provide the required energy. This continues to occur until the ribosome reaches the stop codon at the end of the mRNA molecule and this stop codon does not code for an amino acid so the ribosome detaches and translation ends, polypeptide is made
Summarise the function of mrna and where it is in the body
A short stranded molecule found in both the cytoplasm and the nucleus, made during transcription in the nucleus, this is copied from DNA and is therefore complementary to the DNA sequence, in the mRNA groups of 3 bases are called codons
Describe and summarise the main function and location of tRNA
These are found in the cytoplasm and have amino acids attached to them, each tRNA have one amino acid determined by the anticodon attatched to it ( three bases) Each tRNA molecule has an anticodon that is complementary to the codons on mRNA, and this is involved in translation, it carries the amino acids that are used to make proteins to the ribosomes
Describe the structure of tRNA
A single polynucleotide strand that is folded into a clover shape, hydrogen bonds between these base pairs hold this shape
Has amino acid on one side with anticodons on the other side
What causes the unzipping of DNA strand during transcription
The enzyme DNA helicase, which breaks the hydrogen bonds between bases
Give the 2 stages of which occur during spicing
The pre MRNA has a cap added, on the 5 end of the mRNA, and at the 3 end a poly A tail is added which is several adenine nucleotides, both of these modifications protect both ends of the mRNA from being hydrolysed by endonuclease enzymes
The second modification is the removal of junk DNA or introns, removed by spliceosomes
Describe how a single amino acid is added to a polypeptide chain during translation
- Trna molecule will bring the specific amino acid to the ribosome
- The anticodon on the trna molecule will bind to the codon on the mrna molecule
- These amino acids will join to form a peptide molecule
- This using energy released by ATP
Describe how a single strand of mrna is formed in the nucleus, no splicing or dna helicase in the answer ( 3 marks)
- Free rna nucleotides will form complementary base pairs , AU and CG
- Phosphodiester bonds will form between each individual nucleotide
- By the actions of RNA polymerase
