Protein Synthesis + Homeostasis Flashcards
What is a gene?
Genes are sections of the DNA molecule which codes for proteins and RNA
How do genes express themselves (gene expression)?
Expressed in terms of the proteins they produce.
What is a chromosome composed of?
A DNA molecule which is wrapped around histone proteins.
What will happen if a gene is faulty?
It will create the wrong substance.
What are the properties of the DNA triplet code?
- Degenerate (redundant): More than one code can code for the same amino acid. If one code malfunctions, other code can compensate.
- Unambiguous: A particular code can code for only ONE amino acid.
- Non-overlapping: The code is read in groups of 3.
- Universal: The codes code for the same amino acid in almost all living cells.
What are the 2 stages of protein synthesis?
1) Transcription- the base sequences in the DNA (triplet codes) are transcribed onto an mRNA molecule as codons.
2) Translation- the base sequence (codons) of the mRNA is used to produce the amino acid sequence of a polypeptide chain which folds to become a protein.
What happens during transcription?
- Sections of the DNA containing the required genes unwind exposing a group of nucleotides.
- Nucleotides containing the complementary bases assemble opposite the exposed bases of the template (transcribing) strand.
- The pre-mRNA that is synthesized contain both exons (expressed) and introns (interruptions). The introns are spliced off and the exons combine to form the final mRNA which travels to the ribosomes via a nuclear pore.
- The exposed part of the DNA rewinds.
- The enzyme involved in transcription is RNA polymerase.
- Transcription takes place from the 5’ to the 3’ end of the m-RNA
What happens during translation?
- The m-RNA travels towards the ribosomes via nuclear pores to be ‘read’.
(Ribosomes are composed of proteins and r-RNA). - The instructions on the m-RNA carry:
a. codons for respective amino acids
b. start and stop codons.
(The start codon AUG codes for methionine but the three stop codons UAA, UAG, UGA, do not code for an amino acid.)
- t- RNA molecules in the cytoplasm contain an anti-codon at one end and a specific amino acid attachment site at the other end (the 3’ end).
- When the codons are ‘read out’ the t-RNA with the complementary anti-codon brings the respective amino acid to the site of synthesis.
- t-RNA returns to the cytoplasm to gather more amino acids.
- The amino acids which are brought to the site form peptide bonds with each other which results in a polypeptide chain.
How does transcription and translation occur in prokaryotes?
- Since Prokaryotes do not have a nucleus, transcription and translation occur SIMULTANEOUSLY in the cytoplasm.
- The process is faster than in the Eukaryotes.
Where does protein synthesis take place?
In the ribosomes which are found either in the cytoplasm or on the Rough Endoplasmic Reticulum.
What enzyme catalyses the unwinding of the section of the DNA that contains genes?
DNA Helicase.
What happens once DNA is unwound?
RNA nucleotides assemble opposite the complementary nucleotides of the template DNA strand. In this manner, the DNA triplet codes are copied onto mRNA molecule. This process is called transcription.
What is the junk that is copied onto the mRNA and then spliced off called?
Introns.
How does pre-mRNA and functional mRNA differ?
Pre-mRNA contains both introns and exons whereas the functional mRNA contains only exons with the addition of a methylated cap and a poly-A tail.
What is the difference between a polypeptide chain and a protein?
A polypeptide chain is formed during translation whereas a protein is a folded polypeptide chain.
