2: Transcription and Translation Flashcards
What is the sequence of bases in a polypeptide determined by? How is this sequence stored?
- the base sequence of a gene
- in a coded form
What is the first stage in the synthesis of a polypeptide?
to make a copy of the base sequence of the gene
When synthesising a protein, what is the copy of the base sequence of the gene made from? Where does the copy go? What is it called
- RNA
- RNA is carried to the ribosomes in the cytoplasm to give them the information needed to synthesize a polypeptide, so is called mRNA (messenger RNA)
What is ‘transcription’ of DNA?
the copying of the base sequence of a gene by making an RNA molecule
When does transcription begin?
when the enzyme RNA polymerase binds to a site on the DNA at the start of a gene
Describe the process of transcription.
(Stages 1, 2, and 3 carried out by RNA polymerase)
- RNA polymerase moves along gene separating the DNA into two single strands
- RNA nucleotides are assembled along one of two strands of DNA. Same rules of complementary base pairing are followed as in replication, except that uracil pairs with adenine, as RNA does not contain thymine
- RNA nucleotides are linked together by covalent bonds between the pentose sugar of one nucleotide and the phosphate of the next
- RNA strand separates from the DNA strand as it is produced and is released completely when the end of the gene is reached
- DNA strands pair up again and twist back into double helix
What can be deduced from the base sequence of a strand of mRNA?
the base sequence of the DNA strand from which it was transcribed
What is the ‘sense strand’? Explain the term.
- sense strand = strand of DNA that is not transcribed
- sense strand is the same as mRNA (apart from having T instead of U) that is why it is called ‘sense’
Which strand of DNA is the mRNA transcribed from?
the antisense strand
What is ‘translation’ with regard to DNA?
the synthesis of polypeptides on ribosomes, using mRNA and tRNA
What does the mRNA determine in translation of DNA?
the amino acid sequence of the polypeptide (it is being used to make)
What does the ribosome do in translation of DNA?
translates a genetic code called the triplet code - three bases code for one amino acid
What is a codon?
a group of three bases
What does translation of DNA depend on?
complementary base pairing between codons on mRNA and anticodons on tRNA
Draw and label a diagram of translation. Also indicate 4 points of interest. (p30)
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basically this was awkward to turn into a flashcard:
- learn how to draw diagram on p30
- the “points of interest” (PofI) are the 4 bits of writing
- learn to label the PofI, but just write 1, 2, 3, or 4.
- in the upcoming flashcards, you will learn what occurs at each point of interest
- in the exam you will have to adapt this knowledge to fit the question
