62-64; 238-239; 304-305; 307-315 Flashcards
antiparallel
one strand of DNA that runs in the 5’ -> 3’ direction while the other strand was oriented 3’ -> 5’.
double helix
when the antiparallel strands are twisted together. The coiled sugar-phosphate backbones end up on the outside of the spiral and the nitrogenous bases on the inside.
For the bases from each backbone to fit in the interior of the 2.0-nm-wide structure
they have to form purine-pyrimidine pairs. The pairing allows hydrogen bonds to form between certain purines and pyrimidines. Adenine forms hydrogen bonds with thymine, and guanine forms hydrogen bonds with cytosine.
The A-T and G-C bases were said to be complementary
Two hydrogen bonds form when A and T pair, and three hydrogen bonds form when G and C pair. A-C and G-T pairs allowed no or only one hydrogen bond.
Complementary base pairing
also known as Watson-Crick pairing. A-T and G-C.
The nitrogenous bases in the middle of the molecule
are hydrophobic. Twisting into a double helix minimizes contact between the bases and surrounding water molecules.
van der Waals interactions
in addition to hydrogen bonding; between the tightly stacked bases in the interior further contribute to the stability of the helix.
DNA
as a whole is hydrophilic and water soluble because the backbones contain negatively charged phosphate groups that interact with water.
Outside of the helical DNA molecule
molecule forms two types of grooves. The larger of the two is known as the major groove and the smaller one is known as the minor groove.
DNA is stabilized by
hydrophobic interactions in its interior and by hydrogen bonding between the complementary base pairs A-T and G-C.
DNA carries the information required
for the organism’s growth and reproduction.
Theory of chemical evolution
holds that life began once a molecule emerged that could make a copy of itself.
DNA’s primary structure serves as a
mold or template for the synthesis of a complementary strand. DNA contains the information required for a copy of itself to be made.
(1) Copy of DNA:
Heating or enzyme-catalyzed reactions can cause the double helix to separate.
(2) Copy of DNA:
Free deoxyribonucleotides form hydrogen bonds with complementary bases on the original strand of DNA – also called a template strand. As they do, their sugar-phosphate groups form phosphdiester linkages to create a new strand – also called a complementary strand. The 5’ -> 3’ directionality of the complementary strand is opposite that of the template strand.
(3) Copy of DNA:
Complementary base pairing allows each strand of a DNA double helix to be copied exactly, producing two identical daughter molecules.
gene expression
the process of converting archived information into molecules that actually do things in the cell.
Beadle and Tatum
idea was to knock out a gene by damaging it and then infer what the gene does by observing the phenotype of the mutant individual.
Knock-out, null, or loss-of-function alleles
alleles that do not function.
One-gene, one-enzyme hypothesis
claimed that each gene contains the information needed to make an enzyme.
Metabolic pathway
organisms synthesize arginine in these series of steps.
Genetic screen
any technique for picking certain types of mutants out of many randomly generated mutants.
Pyrimidines
thymine and cytosine.
Purines
adenine and guanine.
Crick
DNA was only an information-storage molecule and the instructions it contained would have to be read and then translated into proteins. Proposed that different combinations of bases could specify the 20 amino acids.
Jacob and Monod
suggested that RNA molecules act as a link between genes and the protein-manufacturing centers. Predicted that short-lived molecules of RNA, which they called messenger RNA (mRNA), carry information out of the nucleus from DNA to the site of protein synthesis.
RNA polymerase
È catalyzes the synthesis of RNA; polymerizes ribonucleotides into strands of RNA. Synthesizes RNA molecules according to the information provided by the sequence of bases in a particular stretch of DNA. Does not require a primer.
central dogma
summarizes the flow of information in cells. States that DNA codes for RNA, which codes for proteins.
The sequences of bases in DNA specifies the
sequence of bases in an RNA molecule, which specifies the sequence of amino acids in a protein. In this way, genes ultimately code for proteins.
proteins
enzymes, motors, structural elements, transporters, and molecular signals.
central dogma steps
(1) DNA is transcribed to RNA by RNA polymerase. Transcription is the process of copying hereditary information in DNA to RNA.
(2) Messenger RNA is translated to proteins in ribosomes. Translation is the process of using the information in nucleic acids to synthesize proteins.
process??? idkt he name srry
DNA (info storage) -> (transcription) mRNA (info carrier) -> (translation) proteins (active cell machinery)
An organism’s genotype is determined by
the sequence of bases in its DNA, while its phenotype is a product of the proteins it produces.
Alleles of a gene differ in their DNA sequence.
As a result, the proteins produced by different alleles of the gene may differ in their amino acid sequence.
Changes to central dogma:
(1) Many genes code for RNA molecules that do not function as mRNAs – they are not translated into proteins.
(2) In some cases, information flows from RNA back to DNA.
Reverse transcriptase
specialized viral polymerase; synthesizes a DNA version of the RNA genes. In these viruses, information flows from RNA to DNA.
genetic code
rules that specify the relationship between a sequence of nucleotides in DNA or RNA and the sequence of amino acids in a protein.
triplet code
three-base code.
codon
group of three bases that specifies a particular amino acid.
reading frame
sequence of codons.
Nirenberg and Matthaei
developed a method for synthesizing RNAs of a known sequence. Later devised a system for synthesizing specific codons.
start codon
AUG; signals that protein synthesis should begin at that point on the mRNA molecule. Specifies the amino acid methionine.
stop codon
UAA, UAG, UGA; also called termination codons. Signal that the protein is complete, they do not code for any amino acid, and they end translation.
RNA contains uracil instead of
thymine.
All amino acids except methionine and tryptophan are coded by
more than one protein.
A single codon never
codes for more than one amino acid.
Once the ribosome locks onto the first codon
it then reads each separate codon one after another.
With a few minor exceptions, all codons specify
the same amino acids in all organisms.
When several codons specify the same amino acid
the first two bases in those codons are almost always identical.
If a mutation in DNA or an error in transcription or translation affects the third position in a codon
it is less likely to change the amino acid in the final protein.
Using the genetic code and the central dogma, biologists can:
(1) Predict the codons and amino acid sequence encoded by a particular DNA sequence.
(2) Determine the set of mRNA and DNA sequences that would code for a particular sequence of amino acids.
mutation
any permanent change in an organism’s DNA. Modification in a cell’s information archive – a change in its genotype. Creates new alleles.
point mutation
single-base change.
missense mutations
when the change of a single base pair causes the substitution of a different amino acid in the resulting protein
silent mutation
point mutation that does not change the amino acid sequence of the gene product.
frameshift mutation
point mutations that disrupt major portions of a protein.
nonsense mutation
È occur when a codon that specifies an amino acid is changed by mutation to one that specifies a stop codon. Causes early termination of the polypeptide chain and often results in a non-functional protein.
mutations are divided into three categories:
(1) Beneficial – some mutations increase the fitness of the organism in certain environments.
(2) Neutral – mutation that has no effect on fitness. Silent mutations are usually neutral.
(3) Deleterious – mutations that lower fitness.
Majority of point mutations are
slightly deleterious or neutral.
If point mutations alter DNA sequences that are important for gene expression
they can have important effects on phenotype even though they do not change the amino acid sequence of a protein.
polyploidy
increase in the number of each type of chromosome.
aneuploidy
addition or deletion of individual chromosomes. Result from moving chromosomes into daughter cells during meiosis or mitosis. Doesn’t change DNA sequences, but alter the number of chromosome copies.
inversion
when chromosome segments become detached when accidental breaks in the chromosomes occur. The segments may be flipped and rejoined.
translocation
when chromosome segments become attached to a different chromosome.
deletion
when a segment of chromosome is lost.
duplication
when additional copies of a chromosome segment are present.
Chromosomes of cancer cells exhibit
deleterious chromosome mutations that include aneuploidy, in- versions, translocations, deletions, and duplications.
karyotype
complete set of chromosomes in a cell.
