transcription of dna to rna

transcription

DNA is located in the nucleus. Proteins are made on ribosomes in the cytoplasm. Remember that information in a gene is converted into mRNA, which carries the information to the ribosome. In the nucleus, mRNA is created by using the DNA in a gene as a template. A template is a model provided for others to copy. The process of constructing an mRNA molecule from DNA is known as transcription ( Figure 1.1 and Figure of double stranded DNA. In transcription, only one strand of DNA is used as a template. First, the double helix of DNA unwinds and an enzyme, RNA Polymerase, builds the mRNA using the DNA as a template. The nucleotides follow basically the same base pairing rules as in DNA to form the correct sequence in the mRNA. This time, however, uracil (U) pairs with each adenine (A) in the DNA. For example, a DNA sequence ACGGGTAAGG will be transcribed into the mRNA sequence UGCCCAUUCC. In this manner, the information of the DNA is passed on to the mRNA. The mRNA will carry this code to the ribosomes to tell them how to make a protein. As not all genes are used in every cell, a gene must be "turned on" or expressed when the gene product is needed by the cell. Only the information in a gene that is being expressed is transcribed into an mRNA. Transcription is when RNA is created from a DNA template. Each gene (a) contains triplets of bases (b) that are transcribed into RNA (c). Every triplet in the DNA, or codon in the mRNA, encodes for a unique amino acid. Base-pairing ensures the accuracy of transcription. Notice how the helix must unwind for transcription to take place. The new mRNA is shown in green.

textbook_image

textbook_image

instructional diagrams

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questions

transcription occurs in a ribosome in the nucleus.

a. true

-->  b. false

all genes in a cell are transcribed into mrna.

a. true

-->  b. false

if a gene sequence is acgtttacaa, what will be the corresponding mrna sequence?

a) tgcaaatgtt

-->  b) ugcaaauguu

c) agcuuuacaa

d) agcuuuagaa

what is one significant difference between transcription and dna replication?

a) the dna unwinds during transcription.

-->  b) in transcription, u pairs with a instead of t pairing with a.

c) the new dna moves to the ribosome.

d) all of the above are significant differences.

which of the following is incorrect?

a) dna does not leave the nucleus.

b) dna provides a template for transcription.

-->  c) all genes are transcribed in each cell.

d) uracil base pairs with adenine.

which best describes a codon?

a) a codon is a triplet of three bases in the gene sequence.

b) a codon is a triplet of three bases in the mrna that codes for a specific gene.

-->  c) a codon is a triplet of three bases in the mrna that codes for a specific

d) a codon is a triplet of three bases in the dna that codes for a specific amino acid.

which best defines an mrna molecule?

-->  a) a molecule that carries the instructions in the dna to the ribosome.

b) a molecule that carries the instructions in the rna to the ribosome.

c) a molecule that carries the instructions in the dna to the nucleus.

d) a molecule that carries the instructions in the mrna to the gene.

diagram questions

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