B1.4.2 - Transcription and Translation
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Define genome
complete set of genes in the cell
Define proteome
The full range of proteins that a cell can make
Define codon
Three bases on mRNA that code for an amino acid
Define anti-codon
Three bases on tRNA that are complementary to the codon on mRNA
Name the process that removes base sequences from pre-mRNA to form mRNA.
Splicing
Give some ways in which the structure of an mRNA molecule is different from the structure of a tRNA molecule.
• mRNA is a single helix where as tRNA is a clover shaped molecule • mRNA do not contain hydrogen bond where as tRNA do • mRNA do not have base pairing where as tRNA do • mRNA has codons where as tRNA has anti-codons • mRNA don’t have an amino acid binding site where as tRNA do
Explain the difference between pre-mRNA and mRNA.
• Pre-mRNA contains introns where as mRNA contains only exons; • mRNA has undergone splicing, pre-mRNA has not.
What is the role of RNA polymerase during transcription?
To join RNA nucleotides together (by forming phosphodiester bonds) to form mRNA
Name the three steps involved in protein synthesis
Transcription Splicing Translation
Describe how mRNA is produced in the nucleus of a cell.
• DNA helicase breaks the hydrogen bonds holding complementary base pairs • One DNA strand acts as a template • Free RNA nucleotides are attracted to DNA template strand. • RNA nucleotides bind to their complementary base pair on the template strand - A>U; C>G • RNA polymerase joins RNA nucleotides together • Pre-mRNA is spliced to remove the introns
Explain the role of the anticodon in protein synthesis.
Anticodons on the tRNA bind to codons on the mRNA Anticodons are complementary to those on the codon So the correct amino acid is brought to the ribosome
Name the organelle involved in translation.
Ribosomes
Describe the role of tRNA in the process of translation.
• Anticodons on tRNA are complementary to specific codons on mRNA • A specific amino acid is bound to the tRNA • This amino acid is carried to the ribosome • Ribosome moves along mRNA. • Peptide bond forms between adjacent amino acids. • Via condensation reaction • Requires ATP. • Ribosome detaches from mRNA when STOP codon reached.
Starting with mRNA, describe how the process of translation leads to the production of a polypeptide.
• The mRNA attaches to a ribosome • Anticodons on tRNA are complementary to specific 3. codons on mRNA • A specific amino acid is bound to the tRNA • This amino acid is carried to the ribosome • Ribosome moves along mRNA. • Peptide bond forms between adjacent amino acids. • Via condensation reaction • Requires ATP. • Ribosome detaches from mRNA when STOP codon reached.
What is a histone?
A protein that DNA forms a complex with to allow it to be condensed into a chromosome.
When chromosomes become visible at the start of cell division, they appear as 2 threads joined at a central point called a…
centromere
The 2 condensed ‘threads’ of DNA that are joined at a centromere and make up a chromosome are called…
sister chromatids
Describe how DNA is packed into a chromosome.
• DNA molecule combines with histones. • DNA-Histone complex begins to coil and fold to form loops. • Loops coil further and pack together to form the chromosome.
What is meant by homologous chromosomes?
• A pair of corresponding maternal and paternal chromosomes. • Their genes (are the same) are at the same loci so they determine the same characteristics.
The total number of maternal AND paternal chromosomes in an organism is called its…
diploid number
If a tRNA is involved what stage of protein synthesis are we looking at?
translation
what shape does a tRNA have?
clover shape
The codon on mRNA is AUG - what will be the complementary DNA and anti-codon?
DNA - TAC anti-codon - UAC
How do new alleles come about?
• Random mutations alter coding sequences. • This leads to changes in the amino acid sequence. • This leads to a different polypeptide with a possibly different function/non-functional.