4A - RNA and Protein synthesis Flashcards
What are the 4 differences between DNA and RNA?
RNA - ribose DNA - deoxyribose
RNA - uracil DNA - thymine
RNA - single stranded DNA - double
RNA - shorter than DNA
What are the 3 types of RNA?
messenger (mRNA)
transfer (tRNA)
ribosomal (rRNA)
What is the function of RNA?
Transfers coded information from the DNA into the cytoplasm where it can be translated into proteins.
What is a codon?
A sequence of 3 bases that codes for an amino acid.
What is RNA?
A single polynucleotide strand.
When is mRNA made?
During transcription.
What does messenger RNA do?
Carries the genetic code from the DNA to the ribosomes where it is used to make a protein during translation.
What are groups of 3 adjacent bases usually called in mRNA?
Codons.
How long does mRNA last?
Has a short lifetime.
What is tRNA involved in?
Translation.
What does tRNA do?
Carries the amino acids that are used to make proteins to the ribosomes.
What shape is tRNA?
Clover-leaf shaped.
What is tRNA?
A single polynucleotide strand that is folded into a clover shape.
What is mRNA?
A single polynucleotide strand.
What does mRNA stand for?
Messenger RNA.
What does tRNA stand for?
Transfer RNA.
What does rRNA stand for?
Ribosomal RNA.
What holds tRNA in its clover shape?
Hydrogen bonds between specific base pairs.
What does every tRNA molecule have?
A specific sequence of 3 bases at one end called an anticodon.
What is an anticodon?
A specific sequence of 3 bases at one end of a tRNA molecule.
What is the specific sequence of 3 bases at one end of a tRNA molecule called?
An anticodon.
What do tRNA molecules have at the opposite end to the anticodon?
An amino acid binding site.
What is the first stage of protein synthesis?
Transcription.
What happens during transcription?
An mRNA copy of a gene is made from DNA.
Where does transcription take place in eukaryotic cells?
Nucleus
Where does transcription take place in prokaryotic cells?
Cytoplasm
Describe the process of transcription in protein synthesis:
RNA polymerase attaches to the DNA double-helix at the beginning of a gene.
The hydrogen bonds between the 2 strands in the gene break, separating the strands, and the DNA molecule uncoils at that point, exposing some of the bases.
One strand is then used as a template to make an mRNA copy.
The RNA polymerase lines up free RNA nucleotides alongside the exposed bases on the template strand. The free bases are attracted to the exposed bases. Specific, complementary base pairing means that the mRNA strand ends up being a complementary copy of the DNA template strand except T is replaced by U.
ONce the RNA nucleotides have paired up with their specific bases on the DNA strand, they’re joined together by RNA polymerase, forming an mRNA molecule.
The RNA polymerase moves along the DNA, separating the strands and assembling the mRNA strand.
The hydrogen bonds between the uncoiled strands of DNA re-form once the RNA polymerase has passed by and the strands coil back into a double-helix.
When RNA polymerase reaches a particular sequence of DNA called a stop signal, it stops making RNA and detaches from the DNA.
In eukaryotes, mRNA moves out of the nucleus through a nuclear pore and attaches to a ribosome in the cytoplasm, where the next stage of protein synthesis takes place.
In eukaryotes, what separates the strands of DNA in transcription?
A complex of proteins including a DNA helicase.
What does RNA polymerase do in eukaryotic cells?
Assembles the mRNA strand.
Does transcription make the same or different products in eukaryotes and prokaryotes?
Different.
Explain why different products are made in eukaryotes and prokaryotes as a result of transcription:
In eukaryotes, the introns and exons are both copied into mRNA during transcription. mRNA strands containing introns and exons are called pre-mRNA. A process called splicing then occurs - introns are removed and the exons joined together - forming mRNA strands. This happens in the nucleus. The mRNA then leaves the nucleus for the next stage of protein synthesis (translation).
In prokaryotes, mRNA is produced directly from the DNA - without splicing taking place as there are no introns in prokaryotic DNA.
What are mRNA strands containing introns and exons called?
Pre-mRNA.
What is splicing?
Introns are removed from pre-mRNA and the exons joined together - forming mRNA strands.
What is the second stage of protein synthesis?
Translation.
Where does translation occur?
In the ribosomes in the cytoplasm.
What happens during translation?
Amino acids are joined together to make a polypeptide chain (protein) following the sequence of codons (triplets) carried by the mRNA.
What are codons also known as?
Triplets.
Describe the process of translation:
The mRNA attaches itself to a ribosome and tRNA molecules carry amino acids to it. ATP provides the energy needed for the bond between the amino acid and the tRNA molecule to form.
A tRNA molecule (carrying an amino acid), with an anticodon that is complementary to the first codon on the mRNA, attaches itself to the mRNA by specific base pairing.
A second tRNA molecule attaches itself to the next codon on the mRNA in the same way.
The 2 amino acids attached to the tRNA molecules are joined by a peptide bond. The first tRNA molecule moves away, leaving its amino acid behind.
The third tRNA molecule binds to the next codon on the mRNA. Its amino acid binds to the first 2 and the second tRNA molecule moves away.
This process continues, producing a chain of linked amino acids (a polypeptide chain), until there’s a stop signal on the mRNA molecule.
The polypeptide chain moves away from the ribosome and translation is complete.
What provides the energy needed for the bond between the amino acid and the tRNA molecule to form?
ATP
What is protein synthesis also called?
Polypeptide synthesis.
What are ribosomes made of and where are they made?
Made of 2 subunits, small and large and are assembled in the nucleolus of the nucleus.
What does rRNA do?
Together with proteins forms ribosomes.
What are the differences in the type of chain in DNA, mRNA and tRNA? How many chains are there?
DNA - double
mRNA - single
tRNA - single
What are the differences in the size of DNA, mRNA and tRNA?
DNA - largest
mRNA - variable
tRNA - smaller
What are the differences in the shape of DNA, mRNA and tRNA?
DNA - double helix
mRNA - single helix
tRNA - single helix
What are the differences in the type of sugar in DNA, mRNA and tRNA?
DNA - deoxyribose
mRNA - ribose
tRNA - ribose
What are the differences in the bases in DNA, mRNA and tRNA?
DNA - ATCG
mRNA - AUCG
tRNA - AUCG
What are the differences in the stability of DNA, mRNA and tRNA?
DNA - very stable
tRNA - more stable than mRNA, less stable than DNA
mRNA - unstable
What are the 4 processes to making a polypeptide?
Transcription, Splicing, Translation, Post-translational modification.
What is post-translational modification?
Proteins often need to be altered before they become fully functional.
Modifications are carried out by other enzymes.
Usually polypeptides are then coiled or folded into a secondary structure, this is then folded to produce the tertiary structure, and additional polypeptide chains are linked to form the quaternary structure.
