4A-DNAS, RNA and Protein synthesis Flashcards
(45 cards)
describe DNA storage in eukaryotic organisims
- contains linear DNA molecules existing as chromosomes found in the nucleus
-DNA is very long but condensed to fit
-DNA is wound by histones (proteins)
how is DNA able to be condensed
wound around histone proteins which is coiled repeatedly into a chromosome
describe DNA storage in prokaryotes
circular and shorter
does not have non coding DNA
DNA in the nucleus are not associated with histones
what is a gene
a sequence of DNA bases that code for a polypeptide (proteins) or functional RNA
how many complementary base pairs form an amino acid
three/ DNA triplet
what do genes code for if not polypeptides
functional RNA
what is functional RNA
RNA molecules other than mRNA
name for non coding sections of DNA
introns
name for coding DNA
exons
allele defenition
a different version of a gene
what is a locus
a fixed position where alleles coding for the same characteristic are found
what is mRNA
-RNA made during transcription
-carries genetic code from DNA to the ribosomes for protein production during translation
-a single polynucleotide strand
what is tRNA
-RNA involved in translation
-carries the amino acids used to make proteins to the ribosomes
-single strand that folds onto itself to make a t shape
-carries anticodons that bind to codons (through the amino acid site on the codons of mRNA)
describe transcription
-RNA polymerase binds to DNA at the start of the gene
-DNA helicase attached to the RNA breaks hydrogen bonds between the two DNA strands, causing DNA to strands to separate and DNA to uncoil
-exposing some bases
-one of the two strands is used as a template for mRNA
-RNA polymerase lines up free RNA nucleotides along exposed bases
-mRNA strands end up being complementary copies of the DNA template
-RNA moves along the DNA separating strands and making mRNA strands
-Hydrogen bonds between the two DNA strands re-form once RNA polymerase moves past and DNA re-coils
-when RNA reaches a stop triplet the made mRNA detaches from DNA
mRNA moves out of the nucleus and attaches to ribosome in the cytoplasm.
what occurs in eukaryotes before translation
splicing
describe translation
-mRNA attaches itself to ribosome and tRNA carries amino acids to it
-tRNA carries an anti-codon which is complementary to the codon on mRNA
-they attach
-two amino acids join by peptide bonds, the first molecule then moves away and the third joins
-this process continues producing a chain of linked amino acids until the stop signal on mRNA is reached
-completed polypeptide chain moves away from the ribosome and translation is complete
why does DNA need to replicate 4
growth
repair
reproduction
cell division/replication
what are the two main enzymes in DNA replication and what do they do
DNA helicase: breaks hydrogen bonds between nitrogenous bases, helping to unwind the DNA
DNA polymerase: catalyses condensation reaction between the phosphate and deoxyribose sugar forming phosphodiester bonds of the sugar-phosphate backbone and joining nucleotides together
what is the function of strong double helix with sugar phosphate backbone on the outside
provides strength and stability and protects bases/hydrogen bonds in the middle
describe semi-conservative replication
-DNA molecule unwinds
-DNA helicase breaks hydrogen bonds between nitrogenous bases causing the two strands to separate
-free nucleotides in the nucleoplasm are attracted to their complementary bases pairs
-the sugar phosphate backbone is re-joined by DNA polymerase that catalyses the condensation reaction and forms phosphodiester bonds
-now two strands of double stranded DNA are made
-because each strand contains half the original DNA this is semi-conservative
-2 identical strands are formed
who proved semi-conservative replication
Meselson and Stahl
who validated DNA structure
Watson and Crick
3 attributes of the genetic code
- it is universal
-it is degenerate (there is repeating)
-non-overlapping
