dna Flashcards
nucleotide
monomer of nucleic acid
What are the components of a nucleotide?
Pentose sugar, phosphate plus organic base which contains nitrogen.
pentose sugar in dna vs rna
dna=deoxyribose
rna=ribose
nucleotide bases are either
purine(two rings)
pyrimidine(one ring)
pyrimidine bases
thymine
cytosine
uracil(rna)
purine bases
adenine
guanine
how are nucleotide bases linked to other molecules
by condensation reactions to form polymers
dna structure
composed of 2 chains linked by base pairs which are complementary
forms a double helix which is only 2nm in diameter
in a chromosome how long is dna
85mm long
dna antiparallel
one srand goes from 5’ to 3’, another goes from 3’-5’, this makes the double helix
functions of dna
replication- has two complementary strands; if two separate 2 more form and each is a template
protein synthesis-sequence of bases represents dna info and determines aa sequence
cell division , daughter cell
dna replication allows
accurate copying for cell division, each daughter cell has an exact copy of genetic info
semi conservative replication
dna is unwound and nucleotides are separated by dna helicase
nucleotide opposite complementary bases on template, hydrogen bonds form and nucleotides link by dna polymerase
each replica is a hybrid of parent and new strand
meselson and stahl
ecoli cultured in 15n and amino acids providing evidence for semi conservative replication
meselson and stahl first gen
dna produced 14n and 15n as it divided once
band produced of a mixture of 14 and 15, but rose a bit because of this
meselson and stahl second gen
two bands produced as the relative abundance of the 14n increases
meselson and stahl third and fourth gen
lighter band gets stronger
hybrid band gets fainter
DNA is a store of
genes, genetic info coded into bases
how does amino acid sequence determine characteristics of an organism
sequences direct amino acids which determine proteins and enzymes which direct reactions which make up characteristics of an organism
dna is a triplet code
it comes in 3s which code foe specific amino acids
how many dna codes are possible
4^3= 64
dna code is non overlapping
each base only is in one triplet, and you read it separately
dna code is degenerate
more than one triplet can encode each amino acid
dna code is unambiguous
same codon does not code for 2+ amino acids
dna code is universal
all organisms have the same triplet codes
dna code is punctuated
there are 3 codons not for amino acids but for STOP CODONS
codons vs triplet of bases
codons is in mrna
triplet of bases is in dna
exons
regions of dna that code for proteins/are expressed
introns
regions of non coding dna that contain blocks of repeated nucleotides
mrna function
transcribes instructions in dna and carries these to ribosomes
trna
clover shape, provides linkage between mrna and amino acids
transfers amino acids to ribosomes
most prokaryotes are continuous
they have no introns/non coding sequences
their entire gene is transcribed and translated
one gene one polypeptide argument
one gene can have a variety of polypeptides because various exons produced by splicing can be cut and stuck in many ways
gene
portion of dna that codes for a polypeptide chain
post translational modification
modification of a polypeptide- can be modified by combination with non proteins
carbohydrates
lipids
phosphates
glycoproteins
lipoproteins
phospho-proteins
example of post translational modification
haemoglobin
has secondary, tertiary and quaternary structure
