Protein synthesis Flashcards
What is a gene?
A length of DNA at a certain locus that carries the code for one or more specific polypeptides.
What is an allele?
A version of a gene
What are the features of the genetic code?
Triplet- read in 3s = 1 codon
Universal - same 3 = same amino acid for all organisms
Non-overlapping- 1st 3 bases read then 2nd 3 read
What is the genetic code?
Universal, non-overlapping, degenerate order of bases in DNA with each triplet coding for a particular Amino Acid known as a codon.
Can you distinguish between the DNA in prokaryotic cells and the DNA in eukaryotic cells?
Comparisons:
Both have polynucleotides
Both joined by phosphodiester bonds
Both contain deoxyribose joined to phosphate
Contrasts:
Eukaryotic DNA is longer
Eukaryotic DNA contains introns. Prokaryotic DNA Doesn’t.
Eukaryotic DNA is linear
Prokaryotic DNA is circular.
Eukaryotic DNA is associated with histones Prokaryotic DNA is not.
Can you describe how a DNA molecule and its associated proteins form a chromosome?
DNA Wraps around histones to form a nucleosome.
A chain of nucleosomes is called chromatin (compacted).
Chromatin is wound up to form a single chromosome.
What is the structure of RNA?
One polynucleotide chain, single stranded, ribose sugar with phosphate group and A/U/C/G, Helical shape, shorter than DNA.
Can you explain what is meant by homologous chromosomes?
Homologous chromosomes are maternal and paternal chromosomes joined at a centromere that contain genetic information.
What is meant by the terms genome and proteome?
Genome: all the genes present in the cell including those in organelles.
The complete Proteome: full range of proteins produced by the genome
Proteome: The range of proteins produced by a cell during a specific set of circumstances.
Can you describe the structure and function of transfer RNA (tRNA)?
2 binding sites AA and anti-codon.
Function: brings correct, specific AA to the ribosome in a sequence to synthesise a protein.
tRNA complementary to mRNA not identical.
Hairpin loop, clover-leaf
Can you explain that the mitochondria and chloroplasts of eukaryotic cells also contain DNA?
Endosymbiotic theory, originally prokaryotes as they contain circular DNA
Can you describe the structure and function of messenger RNA (mRNA)?
Complementary copy of a gene.
Carries the code for assembling the protein.
mRNA is longer
mRNA is straight
mRNA has no H bonds
Where would you find ribosomal RNA (rRNA)?
Nucleolus
Can you explain what happens during transcription?
(Nucleus)
DNA Helicase unzips breaking H bonds causing 2 strands to separate and expose the sensical strand.
Free mRNA bases join to exposed DNA bases on the template strand, complementary base pairing.
Catalysed by RNA polymerase, produces pre-mRNA.
DNA strands rejoin
RNA Polymerase recognises stop codon and releases pre-mRNA.
Introns removed and mRNA leaves the nucleus via a nuclear pore and attaches toa. ribosome in the cytoplasm.
How might a protein be assembled?
DNA transcribed to mRNA
Translated to primary structure.
Folding continues…
Can you explain what happens during splicing? Remember this does not occur in prokaryotes!
Non-coding regions of DNA - Introns are removed and exons are joined together.
Can you explain what happens during translation?
(Cytoplasm)
Ribosome moves along the mRNA strand reading the code 3 bases at a time.
Attached to start codon AUG
tRNA molecules contain an anticodon at one end and an AA specific to the anticodon at the other end. tRNA anticodons bind with complementary mRNA codons.
This brings the AA together in correct sequence to produce primary structure of a protein.
Peptide bonds form between AA in a condensation reaction producing water and tRNA molecules are released (ENZYME AND ATP REQUIRED HERE)
Ribosome moves onto third codon allowing a third AA attached to tRNA to form a peptide bond.
As this happens the first tRNA is released and the ribosome moves past the first codon in the chain.
Can you describe the roles of ribosomes, tRNA, and ATP?
Ribosomes - convert an mRNA sequence into AA sequence
tRNA - Courier of AA specific to an anticodon
ATP - Required for translation, provided by mitochondria
What is a gene mutation?
Change in base sequence or quantity of DNA
How and when do gene mutations arise?
During replication of DNA Randomly/spontaneously
Addition, deletion, substitution of nucleotides
Inversion, Duplication, Translation of a section of a gene
Can you describe the effect of mutagenic agents?
Increase the rate of mutation: ionising , NOX, Tar and polycyclic hydrocarbons in smoke from cigarettes.
What is a substitution mutation and what could the possible effects be?
A change in the base may alter the AA sequence and produce a non-function protein and change its shape.
Often a change in base sequence will produce the same aa sequence due to DNA Degeneracy, this is called a silent mutation, having no effect.
Could change a base to make a stop cordon and terminate the polypeptide chain prematurely, leading to a loss of function.
What is a deletion mutation and what could the possible effects be?
Complete loss of a base resulting in a frame shift
Affecting AA sequence from the point of mutation
What is a chromosome mutation?
Non-disjunction: daughter cells with too many chromosomes fail to separate bivalent in metaphase 1 or homologous chromosomes in metaphase 2.
Down syndrome= non-disjunction of chromosome 21.
