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10 Cards in this Set

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What enzyme is involved in transcription?

RNA polymerase

Explain transcription

RNA polymerase attachesto the DNA double helix at the beginning of a gene. The hydrogen between theDNA between the 2 strands break separating the strands and the DNA moleculeuncoils exposing some of the bases. One of the strands is then used as atemplate to make an mRNA copy. The RNA polymerase lines up free RNA nucleotidesalongside the exposed bases. The free nucleotides attaches to the exposed basesby specific complementary base paring. This means that the mRNA is a complementarycopy of the DNA template strand. Once the RNA nucleotides have paired up withthe specific bases on the DNA strand RNA polymerase joins them together formingan mRNA molecule. The RNA polymerase moves along the DNA separating the strandsand assembling the mRNA strand. When RNA polymerase reaches the stop signal onthe DNA strand it stops making mRNA and detaches from the DNA. In eukaryoticcell the mRNA moves out of the nucleus and attaches itself to a ribosome in thecytoplasms.

Splicing

Splicing is the process where introns are removed and the exons join together formingmRNA strands. This happens before the mRNA leaves the nucleus.

Explain why prokaryotic mRNA isn't involved in splicing

Prokaryotic DNA doesn't contain introns

Expain translation

The mRNA attaches itself to the ribosome and tRNAcarries amino acids to it. ATP provides the energy needed for the bond betweenthe amino acid and the tRNA to form. A tRNA molecule, carrying an amino acid,with an anticodon that’s complementary to the first codon on the mRNA, attachesitself to the mRNA by complementary base pairing. A second tRNA molecule attachesitself to the next codon on the mRNA in the same way. The amino acids attachedto the tRNA molecules are joined by a peptidebond. The first tRNA molecule moves away leaving the amino acid behind. A 3rdtRNA molecule binds to the next codon on the mRNA. Its amino acid binds thefirst two and the second tRNA molecule moves away. This process continuesproducing a chain linked amino acids until there’s a stop signal on the mRNA molecule.The polypeptide chain then moves away from the ribosome and translation iscomplete. s_;8�M�

What is the purpose of transcription?

During transcription an mRNA copy of a gene is made from DNA.

where does transcription take place ?

In eukaryotic cells transcriptiontakes place in the nucleus.


In prokaryotic cells it takes place in the cytoplasm

What is the whole purpose of translation?

Amino acids are joined together to make apolypeptide chain following the sequence of codons carried by the mRNA.

where does translation take place?

In both eukaryotic and prokaryotic cells translation occurs at theribosomes in the cytoplasm.

compare mRNA and tRNA

mRNA tRNA


-Made during -Involved in transcription translation


-Single polynucleotide -Single strand polynucleotide strand


-Single helix shape -Clover shape


-Codon complementary -Anticodon is to DNA triplet complementary to mRNA codon


-Broken down after -Reactivated with a translation new amino acid after translation