Ch. 13 and 14 Flashcards
What are the four nitrogenous bases found in DNA?
- thymine
- guanine
- cytosine
- adenine
What are the four nitrogenous bases found in RNA?
- uracil
- gunaine
- cytosine
- adenine
What are the complementary bases in DNA?
- adenine + thymine (A+T)
- guanine + cytosine (G+C)
What are the complementary bases in RNA?
- adenine + uracil (A+U)
- guanine + cytosine (G+C)
What kind of bond holds nitrogenous base pairs together?
hydrogen bonds
What discovery was Chargaff best known for?
concluding that in natural DNA, the number of G=C and the number of A=T
What are purines?
one of two nitrogenous bases characterized by a 6-membered ring fused to a 5-membered ring
Which nitrogenous bases are purines?
adenine and guanine
What are pyrimidines?
one of two types of nitrogenous bases characterized by a 6-membered ring
Which nitrogenous bases are pyrimidines?
cytosine, thymine, and uracil
What is a semiconservative model?
a type of DNA replication in which the replicated double helix consists of one old strand and one newly made strand
What is helicase?
- an enzyme that untwists the double helix of DNA at replication forks
- separates the two strands and makes them available as template strands
- “scissors” that cut DNA in half
What is DNA polymerase?
- an enzyme that catalyzes the elongation of new DNA by the addition of nucleotides to the the 3’ end of an existing chain
- “builders” that assemble nucleotides on DNA molecules
What is DNA ligase?
- a linking enzyme that fills in the gaps made from Okazaki fragments to make on continuous strand
- “glue” that patches DNA together
What is a replication bubble?
a loop that is generated by the unwinding of the double helix
What is a replication fork?
a Y-shaped region on a replicating DNA molecule where the parental strands are being unwound and new strands are being synthesized
In what direction is DNA always synthesized?
5’-3’ direction
What is a leading strand?
the new complementary DNA strand synthesized continuously along the template strand toward the replication fork
5’-3’ direction
What is a lagging strand?
a discontinuously synthesized DNA strand that elongates by means of Okazaki fragments synthesized away from the replication fork
5’-3’ direction
What is a lagging strand?
a discontinuously synthesized DNA strand that elongates by means of Okazaki fragments synthesized away from the replication fork
5’-3’ direction
What are Okazaki fragments?
- short segments of DNA synthesized away from the replication fork on a template strand
- segments are joined together to make up the lagging strand of newly synthesized DNA
What is the flow of genetic information?
- the “flow” of genetic info from DNA to RNA to proteins
- through transcription and translation, info from genes is used to make proteins
“central dogma”
What is the flow of genetic information?
- the “flow” of genetic info from DNA and RNA
- through transcription and translation, info from genes is used to make proteins
“central dogma”
What are triplets in genetic code?
refers to a set of 3 nucleotide bases that code for a certain amino acid
read 3 at a time to account for all 20 possible amino acids
What is genetic code?
- refers to the instructions contained in a gene that tell a cell how to make a specific protein
- uses 4 nucleotide bases in various ways to create 3-letter codons that specify which amino acid must be made
What is transcription?
- the synthesis of RNA using a DNA template
- occurs in the nucleus of eukaryotes
What is RNA polymerase?
- an enzyme that links ribonucleotides into a growing RNA chain during transcription
- starts transcribing at the promoter
What are the 3 stages of transcription?
- initiation
- elongation
- termination
What is initiation?
transcription
- RNA polymerase binds to DNA’s promoter to begin transcription
- promoter tells RNA polymerase where to settle itself on DNA and begin transcribing
What is elongation?
transcription
- RNA strand gets longer due to the addition of new nucleotides
- RNA polymerase walks along the template strand in 3’-5’ direction
What is termination?
transcription
- the process of ending transcription in which RNA gets signals to stop transcribing
- happens once the polymerase transcribes a sequence of DNA known as the terminator
What is messenger RNA?
mRNA
a type of RNA whose job is to carry protein info from the nucleus to the cytoplasm, where polypeptides are formed
What is RNA splicing?
a process that removes introns from pre-RNA and joins exons together in order to enable translation
What are introns?
non-coding, intervening sequences within a primary transcript that is removed during RNA processing
What are exons?
sequences within a primary transcript that remains in the RNA after RNA processing
What is transfer RNA?
tRNA
- functions as a translator between nucleic acid and protein languages by picking up a specific amino acid and carrying it to the ribosome
- recognizes the appropriate codons in the mRNA
What is an anti-codon?
a group of 3 bases on a tRNA molecule that is complementary to an mRNA codon
What is translation?
- the synthesis of a polypeptide using the genetic info encoded in an mRNA molecule
- includes a change of “language” from nucleotides to amino acids
occurs in ribosomes
How many ribosomal subunits are there?
2; one big and one small
come from the cell’s nucleolus
What is the P site?
- holds the tRNA carrying the growing polypeptide chain
- peptidyl-tRNA
middle site
What is the P site?
- holds the tRNA carrying the growing polypeptide chain
- peptidyl-tRNA
middle site
What is the A site?
- holds the tRNA carrying the next amino acid to be added to the polypeptide chain
- aminioacyl tRNA
entrance site
What is the E site?
the place where the discharged tRNAs leave the ribosome
exit site
What are the 3 stages of translation?
- initiation
- elongation
- termination
What is initiation?
translation
ribosome gets together with the mRNA and the first tRNA so translation can begin
What is elongation?
translation
- amino acids are brought to the ribosome by tRNAs and linked together to form a chain
- composed of 3 steps: codon recognition, peptide bond formation, and translocation
What is termination?
the finished polypeptide is released to go and do its job in the cell
What are the 3 steps of elongation?
- codon regonition
- peptide bond formation
- translocation
What are mutations?
changes in the nucleotide sequence of an organism’s DNA (or in a virus)
What are the 2 types of small-scale nucleotide changes?
- substitution
- insertion/deletion
What is nucleotide-pair substitution?
a type of point mutation that replaces one nucleotide and its partner with another pair of nucleotides
What is insertion/deletion?
additions or losses of nucleotides in a gene
What are silent mutations?
substitutions that have no observable effect on the phenotype
ex: (in a gene) a codon that codes for the same amino acid
What are missense mutations?
substitutions that result in a codon that codes for a different amino acid
What are nonsense mutations?
mutations that change an amino acid codon to one of the 3 stop codons –> shorter and usually nonfunctional protein
What are mutagens?
anything capable of causing a mutation
