3.4.2 DNA And Protein Synthesis Flashcards
What is RNA?
RNA is a polymer made up of nucleotides formed of a ribose sugar, a nitrogenous base and a phosphate group.
What are the RNA bases?
Adenine
Cytosine
Guanine
Uracil
What is the function of RNA?
To copy and transfer the genetic code from the DNA in the nucleus to the ribosomes to synthesise proteins.
Some RNA is combined with proteins to create ribosomes.
What is mRNA?
A copy of a gene from DNA made during transcription
How is mRNA made?
From the anti-sense strand of DNA in the nucleus, before diffusing out of the nucleus through nuclear pores
Why can mRNA get out of the nucleus but DNA can’t?
MRNA only contains the base sequence for one gene, so is much smaller than DNA and is able to diffuse out of the nuclear pores.
Why is mRNA short lived?
It is easily broken down/hydrolysed by enzymes, so does not remain outside of the cell when not needed.
What is a codon?
A triplet of bases on the mRNA molecule that codes for a specific amino acid in the polypeptide chain.
Is RNA single or double stranded?
Single stranded
What does mRNA stand for?
Messenger RNA
What does tRNA stand for?
Transfer RNA
What is tRNA?
The type of RNA which attaches to and transfers specific amino acids to the ribosome to create a polypeptide chain.
What is the role of tRNA?
To attach to and carry amino acids from the cytoplasm to ribosomes in translation
What is the shape of tRNA and how is it held together?
It is a cloverleaf shape that is held in place by hydrogen bonds.
What is the anticodon of tRNA?
A sequence of 3 bases that are complementary to the 3 bases on mRNA, so the specific amino acids are arranged in the correct order.
What does rRNA stand for?
Ribosomal RNA
What is rRNA?
A type of RNA that combines with a protein to make a ribosome.
It is non-coding so has no coding information, but acts as an anchor to force mRNA through the ribosome during translation.
What is protein synthesis?
The process by which proteins are formed from amino acids, that consists of two stages: transcription and translation
What is transcription?
The first stage of protein synthesis where the base sequence on a particular gene is copied onto mRNA in the nucleus.
What is translation?
Where the mRNA Jon’s with a ribosome, and corresponding tRNA molecules bring the specific amino acids that a codon codes for.
What is the proteome?
The entire set of proteins that an organism codes for and synthesises.
Where does transcription take place?
In the nucleus
Describe the process of transcription
DNA helicase unwinds the double helix by breaking hydrogen bonds between bases, so complementary base pairs are broken.
Free RNA nucleotides bind to the exposed bases on the DNA anti-sense strand by complementary base pairing.
RNA polymerase joins RNA nucleotides to create pre-mRNA (a copy of one entire gene).
When the codon that signals to stop is reached, the RNA polymerase detaches and the DNA strand reforms its original double helix shape.
What type of cells does splicing occur in?
Eukaryotic cells
What are introns?
Sections of DNA which are non-coding for amino acids, and therefore not expressed in the final protein
What are exons?
Coding sections of DNA that code for a specific amino acid, so are expressed in the final protein.
Describe the process of splicing
An enzyme called splice some removes the base sequence corresponding to the introns, as they do not code for the synthesis of the polypeptide.
Splicing joins the exons together to form mRNA from pre-mRNA.
What happens after splicing?
The mRNA molecule now moves out of the nucleus via the nuclear pores, and binds to the ribosomes in the cytoplasm.
By what process does mRNA leave the nucleus?
Diffusion- as it moves from a high to low concentration
Describe the process of translation
mRNA attaches to a ribosome in the cytoplasm.
The ribosome attaches to the start codon on the mRNA.
The tRNA molecules with the complementary anticodon to the codon on mRNA bring the specific amino acids to the mRNA molecule..
The amino acids then join by peptide bonds, which requires energy from ATP.
This continues until the stop codon is reached, when the ribosome detaches and translation ends.
What happens after translation?
The polypeptide chain is now synthesised and will enter the Golgi body for folding and modification.
What are the similarities between transcription and translation?
They both involve complementary base pairing
They both involve enzymes
They both involve the formation of bonds
What are the differences between transcription and translation?
Transcription takes place in the nucleus, whereas translation takes place in the cytoplasm.
Transcription does not involve tRNA but does involve mRNA, whereas translation involves both mRNA and tRNA.
Transcription involves both DNA and RNA, whereas translation involves RNA only.
Transcription involves the joining of free nucleotides, whereas in translation, nucleotides are already assembled.
In transcription, mRNA contains introns, whereas, in translation, mRNA does not contain introns.
In transcription, no proteins are made, whereas in translation, proteins are made by assembling amino acids.
In transcription, phosphodiester bonds are formed, whereas in translation, peptide bonds are formed.
In transcription, the enzymes DNA helicase and RNA polymerase are needed, whereas translation requires the enzyme peptidyl transferase.
