Chapter 8 - DNA, genes and protein synthesis Flashcards
what is a gene
a gene is a sequence of DNA bases that code for either a polypeptide or RNA
how are genes involved in making proteins
the order of dna bases on a gene determines the order of amino acids in a particular polypeptide. this polypeptide then determines the primary structure of a protein
How many bases code for one amino acid
three
what is functional RNA
RNA molecules other than mRNA that perform special tasks during protein synthesis
what is a cells genome
the complete set of genes in a cell
what is a cells proteome
the full range of proteins a cell is able to produce
what are most amino acids coded by
between two and six triplets
what will all chains of amino acids start with
methionine the start codon
what will all chains of amino acids include
a stop codon
what does the term non overlapping mean
each base is read only once
what are introns
non coding parts of dna
what is a dna molecule in a prokaryotic cell like
the dna molecules are carries as chromosomes but are shorter are circular
the dna supercoils to fit in the cell
what is eukaryotic dna like
it is a linear molecule that exists as chromosomes
the dna molecule is so long that it must be wound around proteins called histones to fit in the nucleus
this creates compact chromosomes
which organelles in eukaryotic cells also have their own dna
mitochondria and chloroplasts but it is shorter than other dna in the nucleus
what are homologous pairs
pair of matching chromosomes which are the same size and have the same genes
what are alleles
different forms of genes
what is the diploid number
the total number of chromosomes in an organism
how do alleles differ
they contain different base sequences so code for different proteins which create different versions of the same polypeptide
what are exons
sections of genes that code for amino acids
what are non coding repeats
sections of dna that are repeating but don’t code for amino acids
how many different amino acids are there
20
why is dna degenerate
most amino acids are coded for by more than one triplet
why is the genetic code describes as universal
the same triplet codes for the same amino acid in all organisms
how do you get the mRNA sequence from a dna sequence
you use the complimentary base pairs but always switch t for u
what does t stand for
thymine
what does a stand for
adenine
what does g stand for
guanine
what does c stand for
cytosine
what does u stand fo
uracil
what is a codon
a triplet of bases that code for one amino acid
how do you work out tRNA from mRNA
the complimentary pairs
tRNA contains uracil not thymine
how do you work out the sequence of amino acids from a section of mRNA
break it down into codons and use information in the table
how are di nucleotides formed
two nucleotides join together in a condensation reaction between the sugar on one nucleotide and the phosphate on another
what bond is formed in polynucleotides
phosphodiester
what are the purine bases
guanine and adenine
what are the pyrimidine bases
thymine uracil and cytosine
what is RNA made from
a single polynucleotide strand in which each nucleotide is made from a ribose sugar a base a c g u and a phosphate group
function of mRNA
after it is formed through transcription it exits the nucleus through nuclear pores where it travels to the ribosome
it acts as a template for protein synthesis
structure of tRNA
a single stranded molecule which is folded into a clover leaf shape held in place by strong hydrogen bonds between complementary bases
at one end there is an anticodon which is complementary to the triplet on the mRNA and at the other there is an amino acid bonding side
function of tRNA
it carries amino acids used to make proteins to the ribosome
what is transcription
the formation of pre mRNA from dna through complementary base pairing
what is translation
mRNA and tRNA are used to convert the genetic code into the polypeptide chains needed to form proteins
process of transcription
dna helices breaks the hydrogen bonds between nucleotides
this causes the double helix to unravel
one of the strands acts as a template strand
using this ran polymerase attaches
complementary nucleotides form the cytoplasm to the exposed strans
as the polymerase moves through the molecule and assembles the pre mRNA the double helix rejoins behind it and hydrogen bonds reform
when the polymerase reaches a stop codon it stops and detaches
why does pre mRNA need to be spliced in prokaryotes
there are no introns in prokaryotes dna
how are introns removed form eukaryotic dna
splicing
what happens to pre mRNA to make mRNA
it is spliced introns are removes and exons are joined together
what happens to a polypeptide chain after it has been made
it is coiled to form the secondary structure
the secondary structure is coiled to form the tertiary structure
different polypeptide chains are linked to form the quaternary structure
process of translation
a ribosome becomes attached to the mRNA
a trna molecule carrying an amino acid with a complementary anticodon to the codon on the mRNA sequence attaches itself to the mRNA by completmentary base pairing
a second trna molecule attaches to the mRNA in the same way
two amino acids attached to the trna molecules join together with a peptide bond
the first trna molecule moves away leaving the amino acid behind
a third trna molecule attaches to the mRNA
by the same process its amino acid joins to the two amino acids already there
the second trna molecule moves away
this continues until the codon is reached
the polypeptide chain moves away from the ribosome
translation is complete
what differs between amino acids
the r group
do trna molecules have hydrogen bonds
yes
which molecules are made form a single polypeptide strand
mRNA and trna
