Protein synthesis continued
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What is a polypeptide?
A polypeptide is a chain of amino acids linked together by peptide bonds. Polypeptides are coded for by genes.
What is a gene?
A gene is a sequence of nucleotides that forms part of a DNA molecule. Genes contain the instructions for protein synthesis, coding for specific polypeptides.
Describe the universal genetic code.
The universal genetic code refers to the fact that the same codons code for the same amino acids in almost all organisms. This provides evidence for a common ancestor and allows for gene transfer between species.
What is the role of a codon?
A codon is a sequence of three nucleotides (a triplet) that codes for a specific amino acid during protein synthesis. There are also start codons (initiate translation) and stop codons (terminate translation).
Explain the significance of 'start' and 'stop' codons in protein synthesis.
Start codons signal the beginning of translation of mRNA into a polypeptide chain. Stop codons signal the end of translation, causing the ribosome to release the mRNA and the newly synthesized polypeptide.
What does it mean for the genetic code to be 'degenerate'?
The genetic code is degenerate because more than one codon can code for the same amino acid. This provides some protection against mutations as some base changes will still result in the same amino acid being incorporated into the polypeptide.
What enzyme catalyzes the synthesis of mRNA during transcription?
RNA polymerase is responsible for synthesizing mRNA by using a DNA template. It binds to a promoter region on the DNA and moves along the template strand, adding complementary RNA nucleotides.
Describe the roles of mRNA, tRNA, and ribosomes in translation.
mRNA carries the genetic code from DNA to the ribosome. tRNA brings specific amino acids to the ribosome, matching its anticodon to the mRNA codon. Ribosomes provide the site for polypeptide synthesis, catalyzing peptide bond formation between amino acids.
What is a codon, and what does it specify?
A codon is a sequence of three nucleotides on mRNA that specifies a particular amino acid or a stop signal during translation.
What is the function of an anticodon?
An anticodon is a sequence of three nucleotides on tRNA that is complementary to a specific codon on mRNA. It ensures the correct amino acid is added to the polypeptide chain during translation by matching the tRNA to the appropriate codon.
Differentiate between the transcribed (template) strand and the non-transcribed strand of DNA.
The transcribed (template) strand is the DNA strand that RNA polymerase uses as a template to synthesize mRNA. The non-transcribed strand is the DNA strand that has the same sequence as the mRNA (except T is replaced by U) and is not directly involved in transcription.
Describe the process of RNA splicing in eukaryotes.
In eukaryotes, RNA splicing involves the removal of non-coding sequences called introns from the primary transcript (pre-mRNA). The remaining coding sequences, called exons, are then joined together to form mature mRNA.
Define a gene mutation.
A gene mutation is a change in the sequence of base pairs within a DNA molecule. This alteration can lead to the production of an altered polypeptide, potentially affecting the protein's function.
Explain how substitution mutations can affect the polypeptide produced.
A substitution mutation involves replacing one nucleotide with another. This can result in a missense mutation (different amino acid), a nonsense mutation (premature stop codon), or a silent mutation (no change in amino acid).
Explain how insertion or deletion mutations can affect the polypeptide produced.
Insertion or deletion mutations involve adding or removing nucleotides, leading to a frameshift mutation. This alters the reading frame of the mRNA, causing a completely different amino acid sequence to be translated from the mutation onwards, potentially resulting in a non-functional protein.
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