Exam 3 Study Guide Flashcards
(52 cards)
Explain the central dogma of molecular biology
the flow of genetic information
DNA—> RNA—> Protein
Define and explain the relationships between the following terms: genes, genetics, genome, chromosome
Genes: segments of DNA that encode functional products like proteins
Genetics: the study of heredity
Genome: all of the genetic info in a cell
Chromosome: larger pieces of DNA that store essential genetic info
Describe the molecular structure of DNA
two strands held together by hydrogen bonds between complementary bases (A-T, C-G), deoxyribose-phosphate backbone, anti-parallel strands
Explain why the complementary nature of DNA is essential for its replication
DNA is complementary in the sense that a template is needed to replicate DNA. It’s essential for DNA to be complementary because how else would the DNA polymerase know which base is supposed to be in a certain spot.
Explain why DNA replication is semi-conservative
Because new DNA has one strand from the DNA it was made from and one newly synthesized strand
Describe the roles of the following enzymes in DNA replication
o Helicase
o Primase
o DNA polymerase
o RNase
o Ligase
Helicase: “unzips” DNA so it can be used as a template for new DNA
Primase: after the strand has been unzipped RNA primase is used to synthesize an RNA primer that is complementary to the sequence of the template strand
DNA polymerase: adds nucleotides to the growing DNA strand in the 5’ to 3’ direction (reads the strand 3’-5’)
RNase: removes the RNA primer
Ligase: seals together Okazaki fragments on the lagging strand
Explain the occurrence of leading and lagging strands
One strand of DNA is synthesized continuously (Leading strand) and the other is synthesized in short patches (lagging strand)
Describe how replication forks move around a circular bacterial chromosome
One will move in a clockwise fashion while the other moves counter-clockwise
Explain how the cell accesses information stored within DNA
First transcription must occur where RNA polymerase binds to a promoter, then it adds RNA nucleotides to the 3’ end of the growing RNA strand. Lastly, the RNA polymerase and RNA must be released from the DNA. mRNA is a product of this process and will deliver the message created here to tRNA to translate.
Identify the difference between DNA nucleotides and RNA nucleotides
Thymine becomes Uracil in RNA, DNA is double helical while RNA is single stranded
Explain the role of the promoter in transcription
directs RNA polymerase to the start of a gene
Distinguish between DNA polymerase and RNA polymerase
DNA polymerase is involved in DNA replication while RNA polymerase is involved with transcription
Explain what is meant by ‘expression level’
expression level is based on the amount of RNA molecules produced. A highly expressed gene would mean there were many RNA molecules produced.
Explain how the genetic code is used to access information from DNA
The genetic code is used to access information from DNA via tRNA that translates the message within mRNA using codons.
Distinguish between sense codons and nonsense codons
Sense codons code for three complementary bases (an amino acid) while nonsense codons signal the end of a protein sequence.
Describe the structure of ribosomes
protein and RNA, 50S subunit + 30S subunit = 70S ribosome
Explain the role of tRNAs in translation
For each codon, tRNAs have a matching anticodon that transports the appropriate amino acid for incorporation into the growing polypeptide chain
Describe the purpose of the A, P, and E sites within ribosomes
locations for tRNAs to bind
Explain how and why transcription and translation is coupled in bacteria
Since both processes occur at the same time within a bacterial cell, if a change is made to one process, the other will be affected. The rate of transcription by RNA polymerase is coordinated with the rate of translation by the first ribosome
Explain why some, but not all, genes are constitutively expressed
Some genes are constitutively expressed because they are needed for the cell to remain alive and functional.
Explain the terms ‘induce’ and ‘repress’ in regards to gene expression
induce= increased expression of a gene
repress= decreased expression of a gene
Describe the purpose of an operon
Operons ensure that all genes are expressed at the same time and level
Describe the structure of an operon and the roles of the promoter, the operator, the regulatory gene, and the structural genes
Structure: a coding strand, promoter, operator, and structural genes
Promoter: region upstream of the gene where RNA polymerase binds
Operator: region upstream of the gene where the PROMOTER binds
regulatory gene: gene that codes for a regulatory protein (i.e. repressor)
In the case of an inducible operon, explain how the presence of an inducer results in
expression of the structural genes (be sure to include the role of the repressor)
In an inducible operon, its default state is off. This is because the repressor is bound to the operator preventing transcription of structural genes. When there is an inducer, it binds to the repressor and “pulls” the repressor off of the operator enabling the RNA polymerase to bind to the promoter and transcribe the structural genes.
