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4.7a Transcription: Synthesizing RNA
Terms in this set (47)
Copying information from DNA to form RNA molecules
Process involving RNA and ribosomes to produce a new protein.
What are the required structures for transcription?
DNA, ribonucleotides, RNA polymerase
Explain the three steps of DNA transcription.
Initiation (reading), Elongation, Termination.
What does DNA transcription form?
RNA molecules that are complementary to the sequence of nucleotides in the DNA strand being 'read.'
What does each nucleotide have?
A five-carbon sugar ribse, a phosphate, and one of four nitrogenous bases (A, C, G, U.
How does DNA differ from RNA?
DNA is double stranded; RNA is single stranded.
What are the building blocks of RNA?
What is RNA polymerase?
An enzyme that assembles the ribonucleotides by complementary base pairing ribonucleotides with DNA
In transcription, what are the nucleotide base pairings used between DNA and RNA?
T-A; A-U; C-G; G-C
What does the DNA nucleotide Thymine pair with in RNA? (i)
What does the DNA nucleotide Adenine pair with in RNA? (i)
What does the DNA nucleotide Cytosine pair with in RNA? (i)
What does the DNA nucleotide Guanine pair with in RNA? (i)
What can the process of transcription be compared to (as a learning strategy)?
Transcription can be compared to writing down a recipe. The DNA is the recipe book, and a gene is a specific recipe. The recipe book is opened (initiation), the specific recipe is written down (elongation), and the recipe book is closed (termination).
What 3 things are produced during transcription?
Messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal (rRNA).
What is the first step in initiation of DNA?
The DNA must be unwound to "read" it.
What assists in unwinding the DNA?
What is the main enzyme that catalyzes the synthesis of an mRNA molecule?
RNA polymerase is.
At what point does an mRNA molecule begin the transcription process?
At contact with the promoter region associated with a gene.
What is the term used to describe the strand of DNA being copied?
The template strand.
What term is used to describe the strand of DNA that is not copied?
The coding strand.
Does DNA become completely unwound during transcription?
No, it does not. It is split apart temporarily, and rewound after transcription.
What is the term for the process of the RNA polymerase moving along the length of DNA until the entire gene has been transcribed?
What is the main function taking place during elongation?
The DNA template's nucleotide bases are being paired with the RNA's complementary base.
What bond is formed between the DNA template's nucleotide bases and the RNA's complementary bases?
A hydrogen bond
What bond is formed between each ribonucleotide in the new RNA polymer?
A phosphodiester bond
Which nitrogenous base is different in RNA and what does it replace in the DNA?
What bonds break up when termination of transcription is reached?
The hydrogen bonds are broken between the DNA strand and the newly formed mRNA strand.
What is the mRNA a 'recipe' for making?
It is a recipe for synthesizing a specific protein.
When it is initially synthesized, what term is used for mRNA?
Pre-mRNA (primary transcript).
At what point does pre-mRNA become mature mRNA?
After modification, before leaving the nucleus.
What two strand sections does pre-mRNA include?
a portion of DNA that lies between two exons; noncoding regions in pre-messenger RNA. These are removed during pre-messenger RNA propessing.
A portion of a DNA molecule; that codes for a section of the future messenger RNA molecule; these "coding" regions in pre-messenger RNA are joined together to form mature messenger RNA.
What happens to introns before mRNA mature?
They are spliced out (removed).
What happens to exons before mRNA matures?
Exons are subsequently spliced together.
What catalyzes the process of splicing?
A ribonucleoprotein molecule complex (composed of RNA and protein) called a spliceosome does.
What other modifications can change mRNA?
Capping; addition of a polyA tail.
Unique bonding of a ribonucleotide containing guanine to the lead end of the mRNA.
What is the function of capping?
It increases the stability of an mRNA strand helping to prevent its digestion by nucleic acid digesting enzymes (nucleases) that are present within the cytoplasm.
Removal of terminal segments of the mRNA and placing numerous adenin-containing ribonucleotides at the tail end of the mRNA.
What is the function of the polyA tail?
The polyA tail provides a means of producing more than one mature mRNA transcript, because the segment that is removed and the addition of the polyA tail can be done at different sites.
What other function does the polyA tail serve?
It measures age of the mRNA as an additional function. When only a certain amount of the tail remains, nuclease enzymes will destroy the mRNA.
When does the mRNA exit the nucleus?
After modification, when it becomes mature mRNA.
How does the mature mRNA leave the nucleus?
Through the nuclear pores.
Where does the mature mRNA go to after leaving the nucleus?
It goes to the ribosome for translation (the second event of protein synthesis).