Genetic information, variation and relationships between organisms Flashcards
what is the genetic code?
the sequence of base triplets/codons in mRNA that code for specific amino acids
what are the features of the genetic code?
- it is non-overlapping so each triplet is only read once
-it is degenerate so more than one triplet can code for the same amino acid
-it is universal so same bases and same sequences used by all the same species
-it is one direction so triplets always read in one direction
define gene
a sequence of bases on a DNA molecule that codes for a specific sequence of amino acids to make a polypeptide chain
define proteome
the full range of proteins that a cell is able to produce at a given time
define locus
the fixed position on a DNA molecule occupied by a gene
define allele
different version of the same gene found on the same locus of a chromosome
describe transcription
-dna helicase breaks hydrogen bonds between the complimentary bases so the double DNA double helix is unwound
-RNA nucleotides align next to their complementary bases on the template strand
-RNA polymerase joins adjacent nucleotides through condensation reactions foring phosphodiester bonds
-when RNA polymerase reaches the stop codon the pre-mRNA detaches from the DNA
-mRNA leaves the nucleus through the nuclear pores
describe splicing
in eukaryotic cells, pre-mRNA must undergo splicing in order to remove introns (Non coding regions) and leave only the exons (coding regions) which are joined back together through condensation reactions
describe translation
-after the mRNA is transcribed it travels through nuclear pores to a ribosome
-the ribosome attaches the start codon of mRNA
-tRNA with the complimentary anti-codon pairs with the codon on the mRNA . this tRNA has a specific amino acid attached
-the ribosome moves along the mRNA, allowing another tRNA to attach to the next codon along.
-the two amino acids which are attached to the tRNA molecules are joined by peptide bonds using an enzyme to catalyse the reaction and ATP which is hydrolysed to supply energy
-the tRNa detaches without its amino acid and the ribosome moves along the mRNA to the next codon
-it continues until a stop codon is reached
what is tRNA?
-tRNA is involved in translation as it carries amino acids to the ribosomes which are then used to make polypeptides
-tRNA is a single polynucleotide
-tRNA is folded into a clover shape
-there are hydrogen bonds between specific base pairs
-it has a specific sequence of three bases at the end called an anticodon and an amino acid binding site at the other end
compare and contrast structure of mRNA and tRNA
-mRNA does not have hydrogen bonds but tRNA does
-mRNA is a linear chain whilst tRNA has a coverleaf shape
-mRNA does not have an amino acid binding site but tRNA does
-mRNa has codons and tRNA has anticodons
define population
-all of the organisms of a particular species that live in the same place
define community
-all of the populations of various species that live in a habitat
define genetic diversity
the number of different alleles of genes in a population
what are the sources of diversity in meiosis?
-crossing over
-independent segregation of homologous chromosomes
outline the steps of crossing over
- non-sister chromatids wrap around each other and join up at the chiasmata
-chromosomes break up at the chiasmata and sections of the chromosomes are exchanged
-final chromatids have the same genes but a different combination of alleles