2.1. Chemical Basis of Heredity Flashcards
• DNA as the Genetic Material • DNA Structure • DNA Organization in Chromosomes • RNA as Genetic Material
what characteristics should a molecule possess for it to serve as the genetic material?
(1) replication
(2) storage of information
(3) expression of information
(4) variation by mutation
what is replication?
a fundamental property of all living organisms; part of cellular reproduction
explain what storage of information is about
the molecule acts as a repository of genetic information wherein it has the ability to encode diverse information
true or false: a molecule always expresses the genetic information it stores.
false. information may or may not be expressed. while most cells contain a complete copy of the organism’s genome, they express only a part of this genetic potential at any point in time. example: bacteria “turn on” specific genes in response to specific environmental conditions; when conditions change, they “turn it off”
what is considered to be the underlying basis of the process of information flow within cells?
expression of (stored genetic) information
detail the process of information flow in cells
(1) transcription of DNA
(2) three main types of RNA are synthesized:
🔸messenger RNA (mRNA)
🔸ribosomal RNA (rRNA)
🔸transfer RNA (tRNA)
(3) translation : mRNA directs the construction of a chain of amino acids, called a polypeptide, which then folds into a protein
explain variation by mutation
🔸mutation, a change in the chemical composition of DNA, is the source of variability among organisms
🔸alterations may be reflected during genetic expression (transcription and translation)
🔸if mutation is present, it may be passed to future generations and with time, become distributed throughout the population
🔸genetic variation provides the raw material for the process of evolution
how are the evidences that DNA is the genetic material classified?
direct
indirect
direct evidences that DNA is the genetic material
(1) avery-mcleod-mccarty experiment
(2) hershey-chase experiment
(3) recombinant dna technology
(4) phage DNA-mediated infection
explain the avery-mcleod-mccarty experiment. how is it a direct evidence?
(1) heat-killed IIIS were used to see if they could transform non-virulent IIR cells into virulent ones
(1) the filtrate was treated with enzymes: DNAse, RNAse, and protease
(2) protease and RNAse treatment: when the heat-killed IIIS cells were treated with protease and RNAse respectively and then mixed with IIR cells, transformation still occurred.
(2) DNAse Treatment: when the heat-killed IIIS cells mixed with IIR cells were treated with DNAse, no transformation occurred.
conclusion : dna is the transforming substance given that no transformation occurred when the dna from the s strain was broken down during the DNAse treatment
species: streptococcus pneumoniae
explain the hershey-chase experiment. how is it a direct evidence?
(1) DNA of the T2 bacteriophages was labeled with radioactive phosphorus-32 (^32P), since DNA contains phosphorus
(2) the protein coat was conversely labeled with radioactive sulfur-35 (^35S), since proteins contain sulfur
(3) the labeled bacteriophages were allowed to infect ecoli. during infection, the phages attach to the bacterial cell and inject their genetic material into it.
(4) after the injection, the mixture was agitated in a blender to separate the phage coats from the bacterial cells and was centrifuged to separate the heavier bacterial cells from the lighter phage coats
(5) radioactive DNA (^32P) was found in the bacterial pellet, indicating that DNA had entered the bacterial cells
(6) radioactive protein (^35S) was found only in the surface, indicating that the protein coats did not enter the bacterial cells
conclusion : the genetic material in T2 phage is DNA
explain how recombinant DNA technology is a direct evidence of DNA being the genetic material
recombinant DNA technology involves splicing together DNA sequences from different organisms. for example, a recombinant DNA molecule is produced when u combine the DNA coding for human insulin with bacterial DNA. when introduced into bacteria, the recombinant dna is replicated and expressed, leading to the production of human insulin. this is a concrete evidence that DNA carries genetic information and codes for specific genes.
explain how phage DNA-mediated infection directly illustrates that DNA is the genetic material
the phage DNA carries all the genetic information needed to produce new phages. this shows that DNA is the genetic material responsible for heredity. for example: hershey-chase experiment
what are the indirect evidences that DNA is the genetic material?
(1) DNA absorbs at the wavelength shown to be mutagenic : (mutagenesis)
(2) DNA is found only where the primary genetic function is known to occur : (distribution of DNA)
explain how mutagenesis (DNA absorbs wavelength shown to be mutagenic) is an indirect evidence of DNA being the genetic material
UV light induces mutations in the genetic material. by irradiating simple organisms like yeast and fungi with UV light at different wavelengths, an action spectrum can be created that shows the mutagenic effectiveness of UV light at various wavelengths. when the action spectrum was compared with the absorption spectrum (shows the amount of light a molecule absorbs strongly), it was found that the wavelengths causing the most mutation (around 260 nm) matched the wavelengths where DNA absorbs the most light, in comparison to protein, which absorbs most strongly at 280 nm
explain how the distribution of DNA (DNA is found only where primary genetic function is known to occur) indirectly shows that DNA is the genetic material
DNA is found only in locations where genetic functions occur (nucleus, mitochondria, chloroplasts), whereas proteins are found throughout the cell, supporting DNA as the genetic material.
a long polymer composed of nucleotides
nucleic acid
true or false: DNA is a nucleic acid
true
what are the building blocks of DNA?
2-deoxyribonucleotides
what are the three components of 2-deoxyribonucleotides?
(1) nitrogenous bases
(2) pentose sugar
(3) phosphate group
two kinds of nitrogenous bases
(1) purines (nine-member-double-ring)
(2) pyrimidines (six-member-single-ring)
types of purines and pyrimidines
purines : adenine and guanine
pyrimidines : cytosine, thymine, and uracil in RNA
what are the pentose sugars in RNA and DNA respectively?
ribose; deoxyribose
differentiate ribose and deoxyribose/2-deoxyribose
ribose has a hydroxyl group in carbon 2 whereas deoxyribose only has a hydrogen atom in carbon 2 (hence, 2-deoxyribose)
structure : cytosine vs uracil vs thymine vs adenine vs guanine
cytosine : NH2 at carbon 4
uracil : carbon 4 is double bonded to oxygen
thymine : methyl group at carbon 5
adenine : NH2 at carbon 6; H at carbon 2
guanine : carbon 6 is double bonded to oxygen; NH2 at carbon 2
what is a nucleoside?
nitrogenous base + pentose sugar
what is a nucleotide?
nitrogenous base + pentose sugar + phosphate group
describe the bonding (n-glycosidic bond) between components of a nucleotide when the base is purine and pyrimidine
purine (double ring) : N-9 atom is covalently bonded to the C1 atom of the sugar
pyrimidine (single ring) : N-1 atom is bonded to the C1 atom of the sugar
in deoxyribonucleotides, the phosphate group is usually bonded to what carbon?
carbon 5
nucleotides are also described by the term ____.
nucleoside monophosphate (NDM); the addition of one or two phosphate groups results in nucleoside diphosphate (NDP) and triphosphate (NTP)
what kind of bond is formed when a nitrogenous base is bonded to a phosphate sugar (C1)?
n-glycosidic bond
what kind of bond is formed when a phosphate group is bonded to only one sugar molecule (C5)?
phosphoester bond