DNA Synthesis, Gene Expression, and Mutation Flashcards
Page 227 Pages 250-258
What is the central dogma of genetics?
genetic information flows in one direction:
1. from DNA
2. transcripted into RNA
3. translation to amino acids and then proteins
What are the four characteristics of genetic material?
- replication
- storage of information
- expression of information
- variation by mutation
What is recombinant DNA technology?
- splicing together DNA sequences from different organisms
What are the components of nucleotides or nucleic acid molecules?
a nitrogenous base, pentose sugar, and phosphate group
What differentiates purines from pyrimidines?
Name the 4 nucleic bases and classify them.
- purines have nine double rings (Adenine and Guanine)
- pyrimidines have six single rings (Cytosine, thymine, and uracil - RNA only)
What is the difference in the chemical makeup of DNA vs RNA?
- DNA contains deoxyribose
- RNA contains ribose
What is semiconservative replication?
DNA is produced by semiconservative replication, which means each new DNA molecule consists of one old and one new strand
* the unwound helix attracts its complementary nucleotide
what is a replication fork?
- the point along the chromosome where replication is occurring
- strands are unwound
- appears at the point of origin of synthesis, then moves along the DNA duplex as replication proceeds
What is a replicon?
the length of DNA that is replicated following one initiation event at a single origin
Is replication unidirectional or bidirectional?
- one direction or in both directions away from the origin?
- DNA replication is bidirectional
- creates two replication forks that move in opposite directions away from the origin of synthesis
What can be used to relax supercoiling during the unwinding process of DNA?
Define supercoiling
- supercoiling: added twists and turns of DNA, caused by coiling tension ahead of the replication fork during unwinding
- DNA gyrase is an exyme that makes single- or double-stranded cuts and catalyzes localized movments that undo the twists and knots that are created during supercoiling
What is the role of DNA helicase?
recruits the holoenzyme to bind to the newly formed replication fork to intiate replication
- then it proceeds to move along the ssDNA (single-stranded), opening up the helix as it progresses
What is the DNA Polymerase III Holoenzyme?
- made up of polypeptide subunits
- the subunits each have different jobs:
- DNA synthesis along template strands
- proofreading
- contains a sliding DNA clamp: encircles the duplex DNA, binds to the DNA polymerase and clamps them together
What is primase?
- an RNA primer
- does not require a 3’-end to initaite synthesis
- builds a primer of RNA to the DNA template for polymerase III to add deoxyribonucleotides
- the RNA primer is later clipped out and replaced with DNA
What is the difference between a lagging and leading strand in DNA synthesis?
- leading strand is the newly synthesized DNA, runs in the 3’ to 5’ direction
- lagging strand runs on the opposite strand, and needs multiple primers to continue running in the 3’ to 5’ direction
What enzyme joins fragments of DNA once RNA primers are removed and Okazaki fragments are united?
Occurs on the lagging strand.
DNA ligase
What are DNA polymerases?
DNA polymerases are enzymes (proteins) involved in DNA synthesis (elongation or polymerization).
What do DNA polymerases I, II, and III require to elongate a DNA strand?
Apart from the appropriate temperature and environment, DNA polymerases require:
all four bases (in the form of deoxyribonucleoside triphosphates: dATP, dTTP, dGTP, and dCTP) and
a DNA template.
What is the role of RNA in DNA synthesis?
None of the DNA polymerases I, II, or III can initiate synthesis although they can elongate an already existing strand, called a primer. The strand they use is, in fact, an RNA strand copied from the DNA template by the enzyme RNA primase, an RNA polymerase that does not require a free 3’ end to initiate synthesis, as do DNA polymerases.
What is the template and coding strand in RNA transcription?
- the template strand is the DNA strand that serves as a template for RNA polymerase
- the coding strand is the complementary DNA strand.
What are introns?
nucleotide sequences that intervene between sequences that code for amino acids
(do not code for anything)
What are exons?
sequences that are expressed in RNA
some are coding, some are non-coding
What is RNA splicing?
the process of remvoing introns form a pre-mRNA and joining together exons
What do the abbreviations STR and VNTR stand for?
STR: Simple tandem repeat.
VNTR: Variable number tandem repeat.
Name three disorders found in humans and due to an abnormal increase in the number of trinucleotide repeats.
Fragile X syndrome, Huntington disease, Myotonic dystrophy, and Kennedy disease.
What is a point mutation?
a change of one base pair to another
a.k.a base substitution
What is a missense mutation?
a change of one mucleotide of a tripelt within a protein-coding portion of a gene that results in the creation of a new triplet that codes for a different amino acid in the protein product
What is a nonsense mutation?
When a nucleotide changes in a triplet that codes for a stop codon, resulting in the termination of translation of the portein
What is a silent mutation?
a point mutation that alters a codon but does not change the amino acid at that position in the protein
What is a transition? What is a transversion?
transition: when a pyrimidien replaces a pyrimidine or a purine replaces a purine
transversion: when a purine replaces a pyrimidine or vice versa.
What is a frameshift mutation?
the insertion or deletion of one or more nucleotides at any point within the gene
- causes the frame of triplet reading during translation to be alteted
What is a null mutation?
a mutation that results in a complete loss of function
What is a recessive mutation?
- results in a wild-type phenotype when present in a diploid organism and the other allele is wild type
- most loss-of-function mutations are recessive
What is a dominant mutation?
- results in a mutant phenotype in a diploid organism, even when the wild-type allele is present
What is a dominant negative mutation?
- can interfere with the function of the product of the wild-type allele
- can reuslt from haploinsufficiency: occurs when one allele is inactivated by mutant, leading the individual with only one functional copy of a gene
What is a suppressor mutation?
Can be intragenic or intergenic - describe both
- a second mutation that either reverts or relieves the effects of a previous mutation
- intragenic mutations are suppressor mutations that occur within the same gene that suffered the first mutation
- intergenic mutations are suppressor mutations that occur elsewhere in the genome
What is the difference between spontaneous and induced mutations?
- spontaneous mutations occur naturally. There are no specific agents associated with their occurance
- induced mutations may be the result of natural or artificial agents (radiation, mineral sources etc.)
What are mutation hot spots?
DNA sequences that appear to be highly susceptible to mutation
What is a polygenic disease?
Variations caused by several genes
What is a monogenic disease
caused by single-gene mutations
Give an example of disorders for the following types of mutations:
- missense
- nonsense
- insertion
- deletion
- trinucleotide repeat expansions
- achondroplastia
- Marfan syndrome
- Familial hypercholesterolemia
- Cystic fibrosis
- Huntington disease
What is a trinucleotide repeat?
- 3 nucleotides consecutively repeated
- they are fragile sites
- recognized in many disorders
What are endonuclease and exonuclease enzymes?
they are repair enzymes that removed incorrect nucleotides and insert the correct one.
endonuclease: creaks a nick in the backbone of the newly synthesized DNA strand
exonuclease: unwinds and degrades the nicked strand until the regio of the mismatch is reaches
What are transposable elements?
- known as “jumping genes”
- DNA sequences that can move or transpose within and between chromosomes
- range from 50 to 10,000 base pairs in length
What are DNA transposons?
they move from one location to another without going through an RNA intermediate stage
* abundant in many organisms including humans and bacteria
What is Crick’s wobble hypothesis?
the prediction that the intitial two ribonucleotides of triplet codes are more critical than the third in attracting the correct tRNA during translation
- makes for a flexible set of base-pairing rules at the third position of the codon
- e.g. GCU, GCA, GCC, GCG all code for Ala
What is the “new dogma”?
sequence implies structure, and structure implies function
What is the protein structure?
B-pleated sheet
* single polypeptide chain folds back on itself, or several chains run in either parallel or antiparallel fashion next to one another
* each structure is stablized by H bonds
