provided earliest evidence that genes are made of DNA
showed DNA is genetic material of a virus
has 4 kinds of nucleotides due to 4 kinds of nitrogenous bases
adenine (A), thymine (T), cytosine (C), guanine (G)
4 kinds of nitrogenous bases in DNA
single-ring structures; nitrogenous bases, T and C
double-ring structures; nitrogenous bases, A and G
purine is always with _____; pyrimidine is always with _____
has OH group attached to the C
has uracil (U) instead of thymine (T)
James Watson and Frances Crick
worked out 3D structure of DNA
double-helix (Two polynucleotide strands wrapped around each other)
structure of DNA
hold strands together
hydrogen bonds between bases ...
a complementary partner
each base pairs with ...
starts with separation of DNA strands
enzymes use each strand as template to assemble new nucleotides into complementary strands
complicated process; some of the helical DNA must untwist
at specific sites on double helix
DNA replication begins ...
origins of replication
specific sites on double helix where DNA begins
each strand of double helix is oriented in ...
links nucleotides by adding 3' end
synthesizes one daughter strand as a continuous piece
connects other strand of double helix
its sequence of DNA bases
an organism's genotype is carried in ...
DNA of a gene is ___ into RNA which is ___ into a polypeptide
genes are codes for ...
protein synthesis takes place in ...
DNA is stored in ...
mRNA, rRNA, tRNA
three types of RNA
triplets of bases--codons
"words" of the DNA "language"
specify the amino acid sequence of a polypeptide
there are __ amino acids and __ nucleotides
adenine (A), Cytosine (C), Guanine (G), Uracil (U)
nucleotides in RNA
Where does transcription occur?
DNA helix unzips and RNA nucleotides line up along one strand of DNA
enzyme that links RNA nucleotides
initiation, elongation, termination
3 steps of transcription
unneeded parts of RNA are cut out
noncoding segments on mRNA
parts of a gene that are expressed
joined together to form continuous coding sequence
Where does translation occur?
ribosome attaches to mRNA and translates its message into a specific polypeptide aided by tRNA
structure allows for picking up appropriate amino acid and recognizing appropriate codon
a base triplet on one end of tRNA; complementary codon on mRNA; recognizes particular codon on mRNA
coordinates functioning of mRNA and tRNA to make polypeptide
consists of two subunits, each made of proteins and rRNA
hold tRNA and mRNA close together during translation
initiation, elongation, termination
3 steps of translation
mRNA, specific tRNA, and ribosome subunits assemble and determine where translation will begin
mRNA binds to small subunit and initiator tRNA binds to ...
codon recognition, peptide bond formation, translocation
3 steps of elongation (translation)
pairs with each codon, adding its amino acids to peptide chain
stop codon reaches A site
elongation continues until ...
any change in the DNA base sequence
causes of mutations
errors in DNA replication or recombination; mutagens
base substitutions, base insertions or deletions
two types of mutations
ultimate cause of diversity in living world
genes packed in protein
must have host cell to replicate
phage DNA enters bacterium and forms a circle; it is replicated, transcribed, and translated; new viral DNA and protein molecules assemble unto new phages, which burst from host cell
phage DNA enters bacterium and forms a circle; phage inserts into host chromosome; DNA is passed on to generations of daughter cells when bacteria divides
have RNA, not DNA as genetic material
have RNA genomes; enter hosts via wounds in outer layers