Biology: Genetics: Transcription and Translation
From DNA instructions to proteins
Biology: Genetics: Transcription and Translation
From DNA instructions to proteins
Biology - Grade 9-12
- 1
State the central dogma of molecular biology and explain what information is transferred at each step.
Focus on the order of the molecules involved.
The central dogma is DNA to RNA to protein. During transcription, information in DNA is copied into RNA. During translation, the information in mRNA is used to build a protein from amino acids. - 2
Transcribe this DNA template strand into mRNA: TAC GGA CTT AAG ACT.
Use base-pairing rules: A pairs with U, T pairs with A, C pairs with G, and G pairs with C.
The mRNA sequence is AUG CCU GAA UUC UGA. RNA uses A, U, C, and G, and it pairs U with A instead of using T. - 3
A DNA coding strand has the sequence ATG TTT CCG TAA. Write the mRNA sequence that would be produced from this gene segment.
The mRNA sequence is AUG UUU CCG UAA. The mRNA matches the coding strand except that uracil replaces thymine. - 4
Translate this mRNA sequence into an amino acid chain using the codon information given: AUG = methionine, GCU = alanine, UUU = phenylalanine, GGA = glycine, UAA = stop. Sequence: AUG GCU UUU GGA UAA.
Read the mRNA in groups of three bases called codons.
The amino acid chain is methionine, alanine, phenylalanine, and glycine. Translation stops at UAA because it is a stop codon and does not code for an amino acid. - 5
Identify the start codon and the stop codon in this mRNA sequence: CCA AUG AAC UGC UGA GGU.
The start codon is AUG, and the stop codon is UGA. Translation begins at AUG and ends when the ribosome reaches UGA. - 6
Explain the role of RNA polymerase during transcription.
Think of RNA polymerase as the enzyme that makes the RNA copy.
RNA polymerase binds to a promoter region of DNA, separates the DNA strands, and builds a complementary RNA strand using one DNA strand as the template. - 7
Describe what happens to pre-mRNA in a eukaryotic cell before it leaves the nucleus.
Pre-mRNA is processed before leaving the nucleus. Introns are removed, exons are joined together, a 5 prime cap is added, and a poly-A tail is added to help protect and export the mRNA. - 8
For the mRNA codon GCU, write the complementary tRNA anticodon.
Anticodons pair with codons using RNA base-pairing rules.
The complementary tRNA anticodon is CGA. The bases pair G with C, C with G, and U with A. - 9
A DNA template strand changes from TAC AAA CCG ATT to TAC AAG CCG ATT. Transcribe both versions into mRNA and determine whether the amino acid changes. Use this codon information: AUG = methionine, UUU = phenylalanine, UUC = phenylalanine, GGC = glycine, UAA = stop.
Transcribe first, then compare the amino acids coded by UUU and UUC.
The original mRNA is AUG UUU GGC UAA, which codes for methionine, phenylalanine, and glycine. The changed mRNA is AUG UUC GGC UAA, which codes for methionine, phenylalanine, and glycine. The amino acid sequence does not change, so this is a silent mutation. - 10
A DNA template strand is TAC GGA CTT ACT. A single base is inserted after the first three bases, making it TAC AGG ACT TAC T. Explain why an insertion mutation can have a large effect on the protein.
An insertion mutation can shift the reading frame, which changes how the mRNA is divided into codons. This frameshift can change many amino acids after the insertion and may create an early stop codon. - 11
Compare where transcription and translation occur in a eukaryotic cell.
Eukaryotic cells have a nucleus that separates DNA from most ribosomes.
In a eukaryotic cell, transcription occurs in the nucleus where the DNA is located. Translation occurs at ribosomes in the cytoplasm or on the rough endoplasmic reticulum. - 12
Explain the functions of the ribosome's A site, P site, and E site during translation.
The A site holds the incoming tRNA carrying the next amino acid. The P site holds the tRNA attached to the growing polypeptide chain. The E site is where the empty tRNA exits the ribosome. - 13
A coding DNA sequence changes from GAG to GTG. The mRNA codon changes from GAG to GUG. Use this codon information: GAG = glutamic acid and GUG = valine. Identify the type of mutation and explain its effect.
A missense mutation changes one amino acid in the protein.
This is a substitution mutation because one DNA base is replaced by another. It is a missense mutation because the codon changes from coding for glutamic acid to coding for valine. - 14
A gene segment has the DNA template strand TAC CGT TTA ATC. Transcribe it into mRNA, then identify the codons.
The mRNA sequence is AUG GCA AAU UAG. The codons are AUG, GCA, AAU, and UAG. - 15
Explain why the sequence of bases in mRNA determines the sequence of amino acids in a protein.
Connect codons to amino acids and amino acid order to protein structure.
The mRNA sequence is read in codons, and each codon specifies an amino acid or a stop signal. Because ribosomes read codons in order, the order of mRNA bases determines the order of amino acids in the protein.