Chapter 1.1 - DNA And Protein Synthesis Flashcards
Define a gene and a genome
A gene is a length of DNA that codes for a specific polypeptide.
A genome is all of the genes in the human body
Compare the structural differences between DNA and RNA. 3 marks
DNA had a deoxyribose sugar whereas RNA only has a ribose sugar.
DNA has the nitrogenous base Thymine present whereas RNA has the base Uracil
DNA has a double helix and RNA only has a single helice
What does triplet code mean and what types are there?
The DNA sequence is a triplet code meaning 3 bases code for one amino acid. There are 64 possible arrangements of the triplet code but only 20 amino acids to code for.
If there are only 20 amino acids but 64 possible arrangements of the triplet code what does it mean?
It means that there are multiple codes for each amino acid. Some triplet codes do not code for an amino acid but rather act as a stop code indicating the end of a polypeptide for the ribosome
What is transcription?
Transcription is the making of mRNA from DNA. mRNA is single stranded and therefore able to leave the nucleus through the nuclear pores and into the cytoplasm to ribosomes. The transcribed mRNA strand is identical to the coding strand of DNA except uracil replaces thymine as bases. The template strand of DNA provides the base sequence for mRNA.
Outline the process of transcription in order.
1) before transcription takes place the DNA strand double helix unzips at the gene to be expressed as a polypeptide
2) the hydrogen bonds between the complementary base pairs of the DNA break and the DNA double helix become two separate helices.
3) there are now 2 strands of DNA: the coding strand is the one which will be copied and sent to the ribosome, and the template strand is used as a template for mRNA.
4) activated mRNA nucleotides free in the nucleus bind to their exposed complementary base pairs of the template strand.
5) the mRNA strand generated moves out of the nucleus via the nuclear pore into the cytoplasm to travel to the ribosomes
What is the second step of protein synthesis?
Translation
What is translation?
Translation is providing information for the correct sequence of amino acids to form a specific polypeptide
Where can the ribosomes be found in a cell
Free in the cytoplasm or on the rough endoplasmic reticulum.
What is tRNA and why is it important?
tRNA is transfer RNA and it is the binding site for both an amino acid and nucleotide bases on the mRNA strand
What is a codon? What is an anticodon?
A codon is 1 base triplet (3bases) which codes for an amino acid and is on the mRNA strand.
An anticodon are the 3 complementary base pairs to the codon on the tRNA molecule
How many tRNA molecules can fit into a ribosome at one time? How many bases is that?
2 tRNA molecules and therefore 6 bases
What is the first codon that for a polypeptide and what is the first anticodon to form hydrogen bonds with it?
The first codon for any polypeptide chain is alway AUG (think August) and therefore the first anticodon on the tRNA will always be UAC and hydrogen bonds will form between the two.
Outline the steps of translation in order
1) A 70-a ribosome consists of 2 sub units. The mRNA molecule attaches itself to the smaller subunit leaving the codons exposed to the larger subunit. The first codon is alway AUG. The appropriate tRNA molecule with the correct anticodon, UAC, arrives and enters the first of 2 spaces in the ribosome, bringing with it the amino acid.
2) the second space in the ribosome allows another tRNA molecule with the correct anticodon for the next codon on the mRNA into the ribosome and bind together with hydrogen bonds. A peptide bond form between the two amino acids present and the first disassociates from the tRNA.
3) the ribosome move along the strand of mRNA one codon and the first tRNA leave the site leaving it’s amino acid behind. The next tRNA molecule arrives and hydrogen bonds form between the complementary bases and peptide bonds form between the new and previous amino acids. The peptide bond formations are catalysed by an enzyme.
4) the ribosome continues to move along the mRNA strand until a stop codon is reached.
