variation and selection Flashcards
what does DNA stand for
deoxyribonucleic acid
where is DNA found
the nucleus of a cell, in the chromosomes
gene
a small section of DNA that determines a particular feature/ codes for a particular protein
does this by instructing cells to produce a particular protein
genome
the entire DNA of an organism
the nitrogenous bases
adenine, thymine, cytosine, guanine
what is DNA made up of
two strands of nucleotides - each containing a sugar molecule, phosphate group and linked by a series of paired nitrogenous base- coiled into a double helix
a sugar-phosphate backbone with complementary nitrogenous bases
DNA replication
- polynucleotide DNA strands separate
- each strand is used as a template for the formation of a new DNA strand
- DNA polymerase assembles the strands into two new strands according to the base pairing rule
- two IDENTICAL DNA molecules are formed -each containing a strand from the parent DNA and the new complementary strand
template strands
actually codes for the manufacture of proteins in a cell
triplet code
the DNA code is a triplet code, a sequence of 3 bases codes for one amino acid e.g TGT codes for the amino acid cysteine
differences between DNA and RNA
- RNA is single strand, DNA is double helix
- RNA contains ribose, DNA contains deoxyribose
- RNA contains the base uracil instead of thymine
two types of RNA
mRNA (messenger RNA): forms a copy of the DNA code
tRNA (transfer RNA): carries amino acids to the ribosomes to make the protein
the two stages of protein synthesis
- transcription
- translation
transcription
enzyme unwinds and unzips a section of the DNA helix, allowing RNA polymerase to create a complementary strand of mRNA
The mRNA carries this copied genetic information out of the nucleus to the ribosomes where proteins are assembled based on this code
translation
takes place in the ribosomes, the code consists of sets of 3 bases in the mRNA called codons. each codon codes for a particular amino acid
the mRNA molecule attaches to a ribosome. the tRNA molecules each have an anticodon of three bases at one end of their molecule, which is complementary to a particular codon on the mRNA. at the other end of the tRNA molecule is a site where a specific amino acid can attach. the tRNA molecule carries its amino acid to the ribosome where its specific anticodon pairs up with the three bases of the corresponding mRNA codon
mutation
a mutation is a rare, random change in genetic material that can be inherited
types of mutations
- duplication
- deletion
- substitution
- inversions
duplication mutation
nucleotide is inserted twice instead of once, entire base sequence is altered, whole gene is different and will now code for an entirely different protein
deletion mutation
a nucleotide is missed out, entire base sequence is altered, whole gene is different and will now code for an entirely different protein
substitution mutation
a different nucleotide is used, triplet of bases in which the mutation occurs is changed and it may code for a different amino acid
inversions mutation
the sequence of the bases in a triplet is reversed, similar effects to substitution, only one triplet is affected
mutagens
agents which increase the rate of gene mutations
examples of mutagens
- ionising radiation (UV light, X-rays, and gamma rays)
- chemicals e.g mustard gas, nitrous oxide, chemicals in cigarette smoke
natural selection
process where certain individuals in a population survive because they are better adapted to their environment. they are more likely to pass on their genes to their offspring
the structure of chromosomes
each chromosome contains one double-stranded DNA molecule. The DNA is folded and coiled so that it can be packed into a small space. the DNA is coiled around proteins called histones
