Chapter 4 - Nucleic Acids and the RNA World Flashcards
what are nucleic acids made of?
nucleotides (monomers)
what are the 3 components of a nucleotide?
1) phosphate group
2) a five-carbon sugar
3) a nitrogenous base (contains nitrogen)
what are two types of nucleotides?
1) ribonucleotides –> ribonucleic acid (RNA)
2) deoxyribonucleotides –> deoxyribonucleic acid (DNA)
what is the sugar component of ribonucleotides?
ribose
what is the sugar component of deoxyribonucleotides?
deoxyribose (deoxy means “lacking oxygen)
purines
type of nitrogenous base
- adenine
- guanine
pyrimidines
type of nitrogenous base
- cytosine
- uracil (RNA)
- thymine (DNA)
what type of nitrogenous base does RNA use?
pyrimidine (uracil)
what type of nitrogenous base does DNA use?
pyrimidine (thymine)
DNA primary structure
the sequence of deoxyribonucleotides
-bases are A,T,G,C
DNA secondary structure
2 DNA strands running in opposite directions held together by complementary base pairing, twisted into a double helix
- stabilized by hydrogen bonding between nitrogenous bases and hydrophobic interactions
- A = T
- G = C
RNA primary structure
sequence of ribonucleotides
-bases are A,U,G,C
RNA secondary structure
short regions of double helices and structures called “hairpins”
- -stabilized by hydrogen bonding between nitrogenous bases (complementary base pairing)
- RNA bases fold over and make hydrogen bond base pairings with bases on the SAME strand
what is more easily made, sugars/purines or pyrimidines/ribose?
sugars and purines are easily made. pyrimidines and ribose are not
what reaction occurs when nucleotides polymerize to form nucleic acids?
a condensation reaction
- this forms a phosphodiester bond
- between 5’ carbon and 3’ carbon of two different nucleotides
qualities of the sugar-phosphate backbone of nucleic acid
-they are directional (one end has an unlinked 5’ carbon/one end has unlinked 3’ carbon)
primary structure of nucleic acid
- the directional nucleotide sequence of the growing molecule
- goes from 5’ –> 3’ (only added to the 3’ end)
qualities of the polymerization of nucleotides
- endergonic (requires energy input, not spontaneous)
- catalyzed by enzymes
- energy used in this process comes from the “phosphorylation” of nucleotides
phosphorylation
- transfer of one or more phosphate groups to a substrate molecule
- raises the potential energy of the substrate
- enables endergonic reactions
why can polymerization take place in cells?
the potential energy of the nucleotide monomers is raised by reactions that add two phosphate groups to either ribonucleotides or deoxyribonucleotides
- this creates nucleoside triphosphates (3 phosphate groups)
** the addition of one or more phosphate groups raises the potential energy of substrate molecules enough to make the reaction possible)
ATP
adenosine triphosphate (“activated” nucleotide) with 3 phosphate groups
2 empirical rules of DNA
- total number of purines and pyrimidines are the same
- the number of A’s = T’s
- the number of G’s = C’s
describe the secondary structure of DNA
- antiparallel configuration, double helix
- hydrophilic sugar-phosphate backbone (exterior facing)
- nitrogenous base pairs (interior facing, A-T and G-C)
- two different sized grooves (major and minor)
what nitrogenous base pairings exist in DNA?
purines always pair with pyrimidines
-complementary base pairs include A-T and G-C
how many hydrogen bonds do A-T pairings have?
2
how many hydrogen bonds do G-C pairings have?
3
how is DNA stabilized?
- hydrophobic interactions in its interior
- hydrogen bonding between complementary base pairs
how does DNA contain biological information?
- language of nucleic acids is contained in the sequence of the bases
- DNA carries info for growth and reproduction of all cells
what makes DNA replication possible?
complementary base pairing (A-T and G-C)
-each strand serves as a template for the formation of a new complementary strand
steps of DNA replication
1) double helix separates
2) each existing strand of DNA serves as the template for a new strand to form. free nucleotides attach to existing 3’ ends according to complementary base pairing
3) polymerization - new strands come together/forms a sugar-phosphate backbone (secondary structure is restored)
is DNA stable? reliable? is it a good catalyst?
-DNA is extremely stable and reliable for storing information
-HOWEVER is it not a good catalyst because it is so stable
(because DNA is not a good catalyst, they think RNA composed the first life form, not DNA)
what are the two functions that the first living molecule would have needed to carry out?
1) carry information
2) catalyze reactions that promoted its own reproduction
how are DNA and RNA similar?
-both have same primary structure (phosphodiester linkages –> sugar-phosphate backbone + sequence of 4 nitrogenous bases extending from the backbone)
what are the two main differences between DNA and RNA?
1) RNA sugar = ribose
DNA sugar = deoxyribose
2) RNA = pyrimidine base is uracil
DNA = pyrimidine base is thymine
is RNA more or less stable than DNA?
less stable!
-OH makes ribose much more reactive and less stable than DNA
can RNA have tertiary and quaternary structures? if so, what are they?
tertiary- folds that form distinct 3 dimensional shapes
quaternary- associations between several RNA molecules
what are some capabilities of RNA?
- intermediate between DNA and proteins
- capable of storing information, self-replicating
- can function as catalytic molecule
ribozymes
enzyme-like RNA’s
RNA replicase
a type of ribozyme
-can catalyze the addition of ribonucleotides to a complementary RNA strand
