B8 Flashcards
what is a gene
a section of DNA that contains the coded information for making polypeptides and functional mRNA
features of genetic code (3)
degenerate, non overlapping, universal
DNA in prokaryotes vs eukaryotes
prokaryotes:
- shorter
- circular
- not associated with histones
homologous pair
two chromosomes that carry the same genes in the same position, but not necessarily the same alleles for the gene
allele
one of many alternative forms of a gene
chromosomes vs chromatin
chromosomes:
tightly packed DNA
only during cell division
DNA not being used in macromolecular synthesis
chromatin:
unwound DNA
found throughout interphase
DNA= being used for macromolecular synthesis
change in 1 base in sequence of an enzyme…
change in base sequence
different triplet
different amino acid coded for
different primary structure
(different polypeptide chain)
different bonds form/ bonds form in diff places
different secondary and tertiary structure
active site has different shape
no longer complementary to substrate
no enzyme substrate complexes made
DNA in chloroplast vs nucleus
DNA is shorter
fewer genes
DNA is circular not linear
DNA is not associated with histones like nuclear DNA
introns are absent but present in nuclear DNA
role of mRNA
transfers DNA code from nucleus to cytoplasm
what is a codon
the sequence of 3 bases on mRNA that code for a single amino acid
genome
the complete set of genes in a cell, including mitochondria/chloroplasts
proteome
the full range of proteins produced by the genome
the structure of mRNA is suited to its function…
it posesses information in the form of a codon (3 bases that are complementary to a triplet in DNA)
the sequence of codons determines the amino acid sequence on a specific polypeptide that will be made.
DNA structure
double polynucleotide chain
largest molecule of the three
double-helix molecule
pentose sugar is deoxyribose
A, T, C, G
mostly found in nucleus
quantity is constant for all cells of a species (except gametes)
chemically very stable
mRNA
single polynucleotide chain
molecule is smaller than DNA but larger than tRNA
single helix (except in a few viruses)
pentose sugar is ribose
A, U, C, G
manufactured in nucleus but found throughout cell
quantity varies from cell to cell and with level of metabolic ability
less stable than DNA or tRNA
individual molecules are usually broken down in cells within a few days
has codons
does not have hydrogen bonds
no amino acid binding site
tRNA
single polynucleotide chain
smallest molecule of the three
clover shaped molecule
pentose sugar is ribose
A, U, C, G
manufactured in nucleus, found throughout cell
quantity varies from cell to cell and with level of metabolic activity
chemically more stable than mRNA but less stable than DNA
has anticodon
has hydrogen bonds
has amino acid binding site
advantage of DNA being stable
DNA needs to pass from generation to generation unchanged
it therefore allows offspring to be similar to their parents
any change in DNA is a mutation and is normally harmful
advantage of mRNA being unstable
mRNA is produced to help manufacture a protein
it would be wasteful to produce the protein continuously when it is needed periodically
mRNA therefore breaks down once used and produced only when next required.
describe how mRNA = formed by transcription in eukaryotes
hydrogen bonds between DNA bases break
one DNA strand acts as a template
free RNA nucleotides align by complementary base pairing
A-U, T-A, C-G, G-C
in RNA, Uracil base pairs with Adenine
RNA polymerase catalyses the condensation reaction, joining adjacent RNA nucleotides
forming phosphodiester bonds
pre-mRNA = spliced to form mRNA
describe how a polypeptide is formed by translation of mRNA
mRNA binds to ribosome
ribosome moves to find start codon
ribosome reads 2 codons at a time- can fit around 2 codons
codons attach to anticodons on tRNA by complementary base pairing
tRNA carries specific amino acid, complementary to mRNA codon
peptide bonds form between amino acids using ATP in condensation reaction
tRNA = released after amino acid joined to polypeptide
the ribosome moves along the mRNA to form the polypeptide
so the process is repeated
