Chapter 8 Flashcards
What is a gene, and what does it code for?
A gene is a segment of DNA that codes for functional products.
What are chromosomes, and what do they physically carry?
Chromosomes are structures containing DNA that physically carry hereditary information.
What is the genetic material in bacteria, and what is its structure?
The genetic material in bacteria is a singular circular chromosome, and it contains short tandem repeats (STRs), which are repeating sequences of noncoding DNA.
What are the three parts of a nucleotide?
A nucleotide consists of three parts: a sugar molecule (deoxyribose in DNA or ribose in RNA), a phosphate group, and a nitrogenous base.
What are the two types of nucleic acid?
The two types of nucleic acids are DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).
What are the four types of nitrogenous bases used in DNA?
The four nitrogenous bases used in DNA are adenine (A), thymine (T), cytosine (C), and guanine (G).
In RNA, Thymine is replaced with Uracil. Uracil binds with adenine(A).
What is the leading strand in DNA replication, and how is it synthesized?
The leading strand is synthesized continuously by DNA polymerase in the 5’ to 3’ direction.
What is semiconservative replication?
Semiconservative replication is a process in which each newly synthesized DNA molecule consists of one original (parental) strand and one newly synthesized strand. This ensures that the genetic information is preserved during replication.
What is the lagging strand in DNA replication, and how is it synthesized?
The lagging strand is synthesized discontinuously, with initiation by an RNA primer. This process creates Okazaki fragments, which are later joined by DNA polymerase and DNA ligase.
What is RNA, and how does it differ from DNA in terms of structure?
RNA is a single-stranded nucleotide that contains a 5-carbon ribose sugar. It contains uracil (U) instead of thymine (T) found in DNA.
What is transcription, and what are its stages?
- Transcription is making mRNA from DNA.
- The stages are initiation (start), elongation (making mRNA), and termination (stop).
Where does transcription happen in eukaryotes, and what happens to mRNA before it leaves the nucleus?
In eukaryotes, transcription occurs in the nucleus. Before leaving, mRNA is processed to remove non-coding parts (introns) and join the coding parts (exons).
In prokaryotes, transcription occurs in the cytoplasm.
How is genetic information encoded in mRNA, and what are codons?
- mRNA uses codons (groups of three letters) to carry genetic information.
- There are 64 codons for 20 amino acids due to degeneracy, where multiple codons can mean one amino acid.
What is the first amino acid? What is the codon for this amino acid?
The first amino acid is Methonine. The codon is AUG. This is the start codon.
What are the three stop codons? Why do these codons cause translation to end?
- UAA
- UAG
- UGA
They are known as nonsense codons and cause translation to stop because the ribosome reads the nonsense codon and releases it, forming a protein.
What are the types of base subsitutions (point mutation)?
- Missense mutation: base substitution results in change in amino acid
- Nonsense mutation: base substitution results in a nonsense (stop) codon
- Frameshift mutation: Insertion or deletion of one or more nucleotride pairs
Where does translation happen, and how is the mRNA code turned into proteins?
- Translation occurs in ribosomes.
- It reads mRNA codons, adds amino acids, and builds a protein chain.
- tRNA molecules with anticodons bring the right amino acids. In bacteria, translation can start before transcription is done.
What is a mutation in DNA?
A mutation is a change in the DNA’s base sequence.
How can a mutation in a gene affect the enzyme it encodes?
A gene mutation can make the enzyme inactive, less active, or even enhance its activity.
What is a base substitution mutation, and what are the types of such mutations?
A base substitution mutation is when one base in DNA changes. Types include:
Missense mutation: Changes an amino acid.
Nonsense mutation: Creates a stop codon.
Frameshift mutation: Inserts or deletes nucleotide pairs, shifting the reading frame.
What are silent mutations, and why might they not affect protein function?
Silent mutations change DNA but may not impact protein function because:
The genetic code’s redundancy may still code for the same amino acid.
The mutation may occur in a non-critical part of the protein.
The changed amino acid may be chemically similar to the original.
What are chemical mutagens, and how do they cause mutations?
- Chemical mutagens:
Nitrous acid and nucleoside analogs, induce mutations by altering base pairing/ replacing normal bases, leading to base pairing errors. - Frameshift mutagens, such as benzopyrene, can also cause mutations.
How does radiation cause DNA mutations, and what’s an example?
Radiation, particularly ionizing radiation (like X-rays and gamma rays), can damage DNA by forming ions that oxidize nucleotides and break DNA strands.
How does UV radiation induce mutations, and what are thymine dimers?
UV radiation causes mutations by creating thymine dimers, where adjacent thymine bases bind together, disrupting DNA structure.
What are two ways DNA can be mutated?
- Spontaneous mutations (DNA polymerase didn’t do a great job proofreading)
- Mutagens (environmental factors like radiation and certain chemicals).
What are the enzymes that can repair mutation damage?
- Photolyases: separate thymine dimers (repairs UV damage)
- Nucleotide excision repair: Enzymes cut out incorrect bases and fill in correct bases
What is the baseline error rate for DNA polymerase?
1/1 Million (10^6)
What is the error rate for DNA polymerase once mutagens are added into the picture?
Increases rate to 1/1 Thousand
What is the difference between horizontal and vertical gene transfer?
- Vertical gene transfer: transfer of genes from an organism to its offspring
- Horizontal gene transfer: transfer of genes between cells of the same generation
The difference is that vertical gives genes to its “kids” whereas horizontal gives genes to “brothers” or “sisters”
Which type of gene transfer
can humans do?
Humans can do vertical gene transfer.
Where does DNA come from in transformation? Do cells need to be in contact for transformation?
In transformation, DNA comes from lysed or dead cells. The cell does not need to be in contact for transformation. It picks up the “naked” DNA from lysed/dead cells.
Genetic Recombination
What is genetic recombination, and what role does it play?
Genetic recombination contributes to genetic diversity within populations and can introduce new functions into organisms.
Genetic Recombination
When does genetic recombination typically occur in a cell?
Genetic recombination occurs after foreign DNA has entered a cell.
Genetic Recombination
What are the four mechanisms of genetic recombination?
- Transformation (DNA from lysed/dead cells make its way into another cell)
- Transduction
- Conjugation (Plasmid replicates from a F+ cell, then gives replicated plasmid to a F- cell)
- Transposons
Genetic Recombination
Explain how transduction works.
- Transduction involves the transfer of DNA from a donor cell to a recipient via a bacteriophage.
- There are two types: generalized transduction and specialized transduction.
Genetic Recombination
What is conjugation, and what is required for it to occur?
Conjugation is the transfer of plasmids from one bacterium to another, requiring cell-to-cell contact via sex pili and compatibility of mating types.
Genetic Recombination
In conjugation, which cell structure transfers the plasmid from one cell to another?
The sex pilli
Genetic Recombination
What happens to the recipient cell after conjugation is complete with a Hfr cell?
When an Hfr donor passes a portion of its chromosome into an F– recipient, a recombinant F– cell results.
Genetic Recombination
What is transferred during conjugation with an Hfr cell?
A portion of the Hfr chromosome is transferred to the recipient cell.
Genetic Recombination
What is a transpon?
- Transposons are segments of DNA that can move within the genome. They contain insertion sequences (IS) that code for transposase, allowing them to cut and reseal DNA.
- Complex transposons may carry additional genes, including those related to antibiotic resistance.
DNA uses what enzyme for replication?
During the process of transcription, what enzyme does RNA use?
- DNA uses DNA polymerase
- Transcription uses RNA polymerase
What is constitutive gene expression? What is inducible gene expression?
- Constitutive gene expression is when we always need to make enzymes no matter the scenerio. (We are always making proteins.)
- Inducible gene expression is when we make enzymes for specific situations.
