DNA, genes and chromosomes Flashcards
in prokaryotic cells
DNA molecules are short, circular and not associated with proteins
in the nucleus of eukaryotic cells
DNA molecules are very long, linear and associated with proteins called histones
together a DNA molecule and its associated proteins form a chromosome
mitochondria and chloroplasts of eukaryotic cells
contain DNA, like the DNA of prokaryotes - short, circular and not associated with proteins
a gene
a gene is a base sequence of DNA that codes for:
the amino acid sequence of a polypeptide
a functional RNA - rRNA and tRNA
it occupies a fixed position called a locus on a particular DNA molecule
a triplet
a sequence of 3 DNA bases - codes for a specific amino acid
the genetic code is universal, non-overlapping and degenerate
nuclear DNA coding in eukaryotes
much of the nuclear DNA does not code for polypeptides
for example - non-coding multiple repeats of base sequences between genes
even within a gene - only some sequences called exons code for amino acid sequences
within the gene, these exons are separated by one or more non-coding sequences called introns
gene
a sequence of DNA bases at a specific locus which codes for a specific polypeptide or a functional RNA
locus
location / position on the chromosomes
allele
an alternative form of a gene
promoter
promoter sequence to indicate start of the gene
introns
are base sequences within the gene that do not code for amino acids
exons
are base sequences that code for amino acids
what are the three components of nucleotides
a pentose sugar
a phosphate group
an organic base
describe the structure of DNA
made up of a deoxyribose sugar, a phosphate group and one of the four organic bases A C G T
it is double stranded
hydrogen bonds between bases form a helix shape
describe the role of DNA
carries genetic information, determines our inherited characteristics
describe the structure of RNA
made up of ribose sugar, a phosphate group and one of four organic bases A C G U
it is single stranded
describe role of RNA
transfers genetic information from DNA to ribosomes for protein synthesis
which bases are purine and which are pyrimidine
purine (double ring) - adenine, guanine
pyrimidine (single ring) - cytosine, thymine, uracil
how is DNA in eukaryotic cells different from in prokaryotic cells
eukaryotic cells = found in nucleus, long and linear, associated with proteins called histones to form chromosomes, mitochondria and chloroplasts contain prokaryotic like DNA
prokaryotic cells = short and circular, not associated with proteins
what is genetic code
the order of bases on DNA
consists of codons (triplets of bases that code for a particular amino acid)
identify features of the genetic code
non-overlapping = each triplet is only read once
degenerate = more than one triplet codes for the same amino acid (64 possible triplets for 20 aa)
universal = same bases and sequences used by all species
what is a gene
a sequence of bases on a DNA molecule that codes for a specific sequence of amino acids to make a polypeptide
can also code for functional RNA
what is a locus
the fixed position on a DNA molecule occupied by a gene
what is an allele
different versions of the same gene, found at the same locus on a chromosome
