Transcription and translation Flashcards
What is mRNAs role?
IT transfers the DNA code from the nucleus to the cytoplasm through nuclear pores in the nuclear envelope where it asssociates with ribosomes which act as a template for protein synthesis. The coded information that it contains is used to determine the sequence of amino acids in the proteins that are synthesised 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, and 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 produced 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 , this is where the 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. The nucleotide bases on one of the 2 DNA strands known as the template strand (antisense strand) , pair with complementary nucleotides from the pool in the nucleus which align with opposite exposed complementary DNA bases. The enzyme RNA polymerase the moves along the strand and joins the nucleotides together to form a pre MRNA molecule, leaving the nucleus through nuclear pores
What is an intron
A section in a gene of DNA that does not code for proteins, these can intervene and prevent the synthesis of a polypeptide
What is an extron
A section of a DNA that does code for proteins
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 an 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 using 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
Describe how transcription forms mrna molecules in the eukaryotic cells ( 5 marks)
- Hydrogen bonds between the DNA bases in the strand will break
- Only one dna strand will act as a template, antisense strand
- Free rna nucleotides join by complementary base pairing , they align opposite the nucleotides on the antisense strand
- In rna uracil is used instead of thymine and will bind with adenine
-RNA polymerase joinds adjacent nucleotides forming phosphodiester bonds - This forms pre mrna which is then spliced to remove introns which may intefere will protein synthesis
What is the bond between complementary base pairs in mrna? ( 1 mark)
Hydrogen bonds
What is the bond between adjacent nucleotides in dna strand? ( 1 mark)
Phosphodiester bonds made by rna polymerase
Describe the formation of a polypeptide by translation of mrna ( 6 marks)
- MRNA attatches to a ribosome at the start codon
- Trna anticodons will bind to the complementary codons on the mrna molecule
- The specific amino acid will be brought along with this
- The amino acids will join by peptide bonds
- Peptide bonds will join through use of ATP
- Trna molecule will be released after this amino acid has joined to the polypeptide
- Then the ribosome will continue to move along the mrna molecule
Describe structural differences between mrna molecules and trna molecules
- TRNA has a clover leaf shape whereas mrna is linea
- MRNA does not have an amino acid binding site whereas trna does
- MRNA has codons, trna has anticodons
Describe the role of ribosomes in translation of a polypeptide
- mrna binds to these ribosomes
- they allos trna molecules with specific anticodons to bind with the complementary codons on the mrna molecule
-Catalyses the formation of amino acids held by trna - moves along mrna to the next codon
Give 2 types of molecule of which a ribosome is made
- A protein molecule and a ribonucleic acid
Define exon
Base sequence that codes for an amino acid
