Transcription and Translation Flashcards
what is the definition of transcription?
-the process of forming complementary copies of mRNA from sequences of DNA that code for a particular polypeptide
what is the molecule that is involved in transcription?
-mRNA
why does DNA always stay in the nucleus?
-less likely to be damaged in the nucleus than in the metabolically active cytoplasm
what is the structure of mRNA?
-single strand
-shorter than DNA
-ribose pentose sugar
-uracil which replaces thymine
what are the steps of transcription?
-DNA helicase separates the two strands of DNA by breaking the hydrogen bonds between base pairs
-RNA polymerase moves along the template strand and links the now exposed nucleotides with ribonucleotides from the nucleotide pool
-following base pairing rules
-the RNA polymerase then links the adjacent ribonucleotides together by phosphodiester bonds
how many nucleotides are exposed at one time during transcription and why?
-because the unzipped DNA rejoins behind the assembly area
when does transcription stop?
-when RNA polymerase reaches a stop codon it detaches and the copying of this polypeptide chain is finished
what are the two sections called that DNA is made up of?
-exons and introns
what are the jobs of exons and introns?
-exons are sections that code for a polypeptide and introns don’t
do prokaryotic cells have introns?
-no they just have exons
how is polypeptides modified to remove the intron and what is this process called?
-introns are removed from the pre RNA and the exons are spliced back together to produce as sequence that codes for the required polypeptide or protein
what is the term given to the mRNA that contains introns?
-pre RNA
what is the definition of translation?
-a process that involves the translation pf the mRNA code into the primary structure
what is the term given to three bases on the mRNA strand that code for an amino acid?
-codon
what are the two components that are involved in translation?
-tRNA and ribosomes
what are some of the characteristics about tRNA? (4)
-single stranded
-clover leaf shaped
-have an anticodon which has complementary bases to the mRNA
-also have exposed nucleotides at the other end that can bind to amino acids
how many different types of amino acids can tRNA attach to and why?
-only one due to their anticodon being specific to the type of bases on the amino acid
what are the two roles of tRNA?
-transport amino acids to the site of protein synthesis
-ensure that each mRNA codon codes for a particular amino acid
where are ribosomes found?
-in the cytoplasm free or attached to the RER
what are the two sections of a ribosome and what are each of the ribosomes made up of?
-large and a small sub unit
-ribosomal RNA and protein
where are the subunits of the ribosome assembled?
-in the nucleolus and are then transported into the cytoplasm
what are the two sites on a ribosome that is concerned with translation and what are their jobs?
-the A site and the P site
-the A site is where tRNA molecules link together through linking the complementary codons and anticodons
-the p site is where adjacent amino acids are linked together by peptide bonds
what is the process of translation?
-ribosome attaches to a start codon by its a site
-tRNA molecule attached to the codon via its complementary anticodon and attaches to its amino acid
-ribosome moves along the mRNA strand to accept another codon which links with the complementary anticodon on the tRNA again the tRNA is carrying its particular amino acid
-the first codon will now be in the p site and a peptide bond will be formed between the first two amino acids
-as the ribosome accepts another codon the tRNA for the first amino acid is set free
-another peptide bond is formed between the second and third amino acid
-this continues till a stop codon is reached
where is the final place that polypeptides are processed and how does it occur?
-in the Golgi Apparatus
-proteins have to be processed before they are pinched off from the concave side of the Golgi
-they are then transported in vesicles to be used in or out of the cell
