topic 4A - DNA, RNA and protein synthesis Flashcards
(18 cards)
how is DNA structured in nuclear eukaryotic cells
1) eukaryotic cells contain linear DNA molecules that exists as chromosomes - thread like structures each made up of one long molecules of DNA. chromosomes are found in the nucleus.
2) the DNA molecules is really so, it has to be wound up so it can fit into the nucleus.
3) the DNA molecule is wound around proteins called histones
4) histone proteins also help to support the DNA
5) the DNA (and protein) is then coiled up very tightly to make a compact chromosome
6) the mitochondria and chloroplasts in eukaryotic cells also have their own DNA. this is pretty similar to prokaryotic DNA because its circular and shorter than DNA molecules in the nucleus. its not associated with histone proteins
how is prokaryotic DNA structured?
1) prokaryotes also carry DNA as chromosomes - but the DNA molecules are shorter and circular
2) the DNA isn’t wound around histones - it condenses to fit in the cell by supercoiling
what is a gene?
a sequence of DNA bases that codes for either a polypeptide or functional RNA
what is the primary structure of a protein?
the sequence of amino acids in a polypeptide
how do you determine the polypeptide?
different polypeptides have a different number and order of amino acids. its the order of bases in a gene that determines the order of amino acids in a particular polypeptide.
whats a triplet?
each amino acid is coded for by a sequence of three bases in a gene
what do genes code for if its not a polypeptide?
they code for functional RNA instead. functional RNA is RNA molecules other than mRNA, which perform special tasks during protein synthesis e.g. tRNA and ribosomal RNA which forms part of the ribosomes
what is a cells genome
this is the complete set of genes in a cell.
what’s a cells proteome?
the full range of proteins that the cell is able to produce
what are introns?
non-coding DNA.
99% of human DNA is non-coding meaning it is not directly involved in protein synthesis.
even some sequences of DNA within a gene do not code for amino acids.
whats an exon?
the parts of genes that do code for amino acids
when are introns removed and why?
introns are removed during protein synthesis - so they dont affect the amino acid order. (prokaryotic DNA doesnt have introns
what is a homologous pair?
pair of matching chromosome. they are the same size and have the same gene, although they have different alleles. alleles coding for the same characteristic will be found at the same fixed position (locus)
What is mRNA?
carried out during transcription.
carry’s out the genetic code from the DNA to the ribosomes, where its used to make a protein during translation.
mRNA is a single polynucleotide strand
in mRNA, groups of three adjacent bases are usually called codons (triplets)
what is tRNA?
involved in translation
carries the amino acids that are used to make proteins to the ribosomes.
tRNA is a single polynucleotide strand that’s folded into a clover shape. hydrogen bonds between specific base pairs hold the molecule in this shape.
every tRNA molecule has a specific sequence of three bases at one end called anticodon. they also have an amino acid binding site at the other end.
what is the process of protein synthesis?
1) DNA - transcription (splicing) in the nucleus
mRNA
2) translation - ribosome
protein
what happens in the first stage of protein synthesis?
Transcription takes place in the nucleus
1) hydrogen bonds between two DNA strands (nucleotides) are Broken by DNA helicase. this separates the strands and the DNA molecule uncoils at that point, exposing the bases
2) RNA nucleotides (strand separated from the DNA) form complimentary base pairs with template DNA strand (base T is replaced with U).
3) RNA polymerase joins the RNA nucleotides so they are joined back together with hydrogen bonds and coil back up into a double helix
4) pre- mRNA is separated from DNA (the remaining strand)
5) pre-mRNA is sliced to remove introns which forms mRNA
what is the second part of protein synthesis?
translation:
1) following the removal of introns the mRNA moves out through a nuclear pore and attaches to a ribosome.
2) a tRNA molecule with an anticodon complementary to the first mRNA codon binds to the mRNA, bringing its specific amino acid
3) A tRNA with an anti-codon complementary to the second mRNA codon binds to the second codon of mRNA, bringing a specific amino acid
4) the two amino acids are joined by a peptide bond, formed by a condensation reaction
5) the tRNA leaves the ribosome, and the ribosome moves along the mRNA to the next codon
6) the process repeats along the length of the mRNA, until a stop
