DNA pt2, translation and transcription, and triplet codes Flashcards
Give 4 differences between prokaryotic and eukaryotic DNA
prokaryotic-
-short with fewer genes
-circular
-not associated with proteins
-no non-coding DNA
eukaryotic-
-long with many genes
-linear
associated with proteins called histones
-non-coding DNA is present
What is a gene?
a base section of DNA that codes for the sequence of amino acids in a polypeptide chain
What is an allele?
a different form of the same gene, found at the same locus on homologous chromosomes
What is a locus?
a fixed position on a particular strand of DNA
What is a trait of homologous pairs?
same genes, same length, potentially different alleles
What is a karyotype?
an image of all chromosomes of an organism in a pair
Each unique gene has…
a unique sequence of bases
What does the unique sequence of bases determine?
the amino acid sequence in the polypeptide
What could happen if there are differences in the base sequences of alleles of a single gene?
potentially a non-functional protein
What is non-coding DNA?
DNA that does not code for polypeptides
What are introns?
a section of eukaryotic DNA that does not code for amino acids
What are exons?
a section of DNA that does code for amino acids
What are multiple repeats?
a section of repetitive DNA formed outside of genes which does not code for amino acids
Where else can DNA be found?
in chloroplasts and mitochondria
What is a genome?
the complete set of genes in a cell
What is a proteome?
the full range of proteins that a cell is able to produce under certain conditions
What are the two major processes involved in proteinsynthesis?
transcription and translation
What is proteinsynthesis?
involves the production of a chain of amino acids that forms the primary structure of a protein
What is splicing?
where the introns are removed by enzymes before the mRNA leaves the nucleus, just leaving the exons
What is the role of ATP in proteinsynthesis?
IN TRANSLATION-
-attaching amino acids to the tRNA
-amino acids are joined by peptide bonds using an enzyme and ATP, which is hydrolysed to provide the required energy
Explain what happens in transcription
-DNA helicase unwinds the DNA by catalysing the hydrolysis of the hydrogen bonds between the bases. one of these is used as the sense strand
-free RNA nucleotides in the nucleoplasm attach themselves to the sense strand by complementary base pairing. only one mRNA strand is made.
-the enzyme RNA polymerase join the nucleotides together
-mRNA strand detaches from sense strand, and the two original DNA strands join together again
-this pre-mRNA strand has lots of non-coding, junk DNA, so is spliced by the enzyme spliceosome, leaving a shorter, mature mRNA strand with only exons
-the mRNA diffuses out of the nucleus through a nuclear pore into the cytoplasm
Explain the process of translation
-tRNA carry SPECIFIC amino acids to the mRNA
-a ribosome attaches to the mRNA at a start codon (AUG). the ribosome encloses two codons (6 amino acids)
-met-tRNA diffuses to the ribosome and attaches to the mRNA start codon by complementary base pairing
-the next amino acid tRNA attaches to the adjacent mRNA codon, by binding it’s anticodon to the codon
-the bond between the amino acid and the tRNA is cut, and instead a peptide bond is formed between the two amino acids, which requires an enzyme and ATP
-the ribosome moves along one codon so that a new amino acid tRNA can attach. the free tRNA molecule leaves to collect another amino acid. the cycle repeats from step 3
-the polypeptide chain is built up one amino acid at a time, folding up the protein as it goes, until a stop codon is reached
What is the name for transcription and translation?
expression
State the 3 properties of the genetic code
universal
degenerate
non-overlapping
What does it mean by universal?
the same sequence of bases codes for the same amino acids in all organisms
What does it mean by degenerate?
each amino acid is coded for by more than one triplet
How do we know that you must read the genetic code in threes?
if it was in 1- only 4 possible amino acids
if it was in 2- only 16 possible amino acids
if it was in 3- 64 possible amino acids
and we know that there are 20 amino acids, so it must be in 3 because its the closest one with enough amino acids
What does it mean by non-overlapping?
it is read in 3s- each base is only part of one triplet/codon
What happens to a polypeptide chain after translation?
structural changes-
-amino acid chain is coiled/folded into secondary and tertiary structures
addition of a non-protein functional group
Why are post-translational modifications necessary?
modifications of the primary structure give the protein it’s specific secondary and tertiary structure that allows it to perform it’s function
