Ch.8 Microbial Genetics Replication and Protein Synthesis

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Questions and Answers

What are the three parts of a nucleotide?

Phosphate, Sugar, Amino Acid

Amino Acid, Phosphate, Nitrogenous Base

Sugar, Amino Acid, Nitrogenous Acid

Phosphate, Sugar, Nitrogenous Base (correct)

Which nitrogenous base pairs with Adenine (A) in DNA replication?

Guanine (G)

Uracil (U)

Thymine (T) (correct)

Cytosine (C)

What term describes the nature of DNA strands running in opposite directions?

Antiparallel (correct)

Counteractive

Bilateral

Conformational

What is the first step of DNA replication?

DNA strands relax and separate Signup and view all the answers

What is the outcome of semiconservative replication?

Two identical DNA molecules, each with one original and one new strand Signup and view all the answers

Which enzyme is responsible for unwinding the DNA during replication?

Helicase Signup and view all the answers

Which sequence correctly represents the base pairing rules?

A-T, C-G Signup and view all the answers

Which component of the DNA structure is reversed in one of the strands?

Sugar orientation Signup and view all the answers

What is the role of nucleotides in DNA?

They serve as templates for DNA replication Signup and view all the answers

What role does lactose play in the lac operon of E. coli?

It binds to the repressor protein, allowing transcription. Signup and view all the answers

Which type of mutation results from a single base being replaced in the DNA sequence?

Point mutation Signup and view all the answers

What is the result of a frameshift mutation in DNA?

All subsequent codons are disrupted. Signup and view all the answers

Which type of mutation results in the introduction of a stop codon in the protein sequence?

Nonsense mutation Signup and view all the answers

What can be the consequence of a harmful mutation?

Reduced survival rate leading to its elimination from the population. Signup and view all the answers

In DNA replication, what can lead to a permanent alteration in an organism's DNA?

Errors during DNA replication or mutagen exposure. Signup and view all the answers

What is the primary function of DNA polymerase during DNA replication?

To add nucleotides and proofread the DNA strand Signup and view all the answers

What characteristic describes the direction of nucleotide addition during DNA replication?

Nucleotides are added only in the 5' to 3' direction Signup and view all the answers

Which enzyme is responsible for sealing the spaces between Okazaki fragments?

DNA Ligase Signup and view all the answers

During bacterial DNA replication, what is the orientation of the leading strand?

Opens in a 5' to 3' direction Signup and view all the answers

What energy supply is utilized during DNA replication?

Nucleotide triphosphates hydrolysis Signup and view all the answers

What is the purpose of helicase in DNA replication?

To unwind and separate the DNA double helix Signup and view all the answers

What problem arises during the replication of the lagging strand?

It must be added in small sections due to the antiparallel nature Signup and view all the answers

How do topoisomerase and gyrase assist in DNA replication?

By preventing DNA supercoiling Signup and view all the answers

What distinguishes bacterial DNA replication from that of eukaryotes?

Bacterial cells undergo faster replication processes Signup and view all the answers

What role does DNA ligase perform during replication?

Seals the sugar/phosphate backbone of DNA Signup and view all the answers

What is the primary function of the P-site during translation?

Binds peptidyl tRNA with amino acid chain Signup and view all the answers

Which step of translation involves the ribosome moving one codon down the mRNA?

Elongation Signup and view all the answers

Which of the following statements about the start codon is true?

It always codes for Methionine. Signup and view all the answers

In which site does the incoming aminoacyl tRNA bind during translation?

A-site Signup and view all the answers

What happens during the termination step of translation?

The ribosome reaches a stop codon. Signup and view all the answers

What role does the large ribosomal subunit play in translation initiation?

It binds to the start codon after the small subunit. Signup and view all the answers

Which amino acid does the start codon AUG specify?

Methionine Signup and view all the answers

What occurs to the tRNA once it has transferred its amino acid in the P-site?

It exits the ribosome. Signup and view all the answers

During which step is the polypeptide chain formed?

Elongation Signup and view all the answers

What is the primary role of transfer RNA (tRNA) during protein synthesis?

To transport amino acids to the ribosome Signup and view all the answers

Which of the following describes a codon?

A three-base sequence in mRNA that encodes a specific amino acid Signup and view all the answers

What is referred to as the 'degenerate code' in relation to genetic coding?

One amino acid is encoded by multiple codons Signup and view all the answers

What is the significance of the anticodon in tRNA?

It binds to the mRNA codon sequence Signup and view all the answers

Which type of ribosome is characteristic of eukaryotic cells?

80s ribosome Signup and view all the answers

Which of the following structures plays a catalytic role in the ribosome's function?

Ribosomal RNA (rRNA) Signup and view all the answers

What happens to the ribosomal subunits after translation is completed?

They float separately in the cytoplasm Signup and view all the answers

What is the primary consequence of a faulty rRNA gene as seen in Treacher Collins Syndrome?

Defects in facial bone development Signup and view all the answers

Which statement best describes the ribosome's interaction with mRNA during protein synthesis?

Ribosomes bind mRNA and serve as a docking station for tRNA Signup and view all the answers

Which of the following roles does the small ribosomal subunit play?

Contains the P-site for amino acid binding Signup and view all the answers

Study Notes

DNA Replication

DNA is made of nucleotides, which are composed of a phosphate, a deoxyribose sugar, and a nitrogenous base (A, T, C, or G)
Two DNA strands are held together by hydrogen bonds between the nitrogenous bases.
The two DNA strands have opposite orientations, one running 5’ to 3’ and the other 3’ to 5’.
DNA replication is semiconservative - each new DNA molecule consists of one original strand and one new strand
DNA replication proceeds in a 5’ to 3’ direction.
Two DNA strands are unwound and separated by the enzymes topoisomerase, gyrase, and helicase.
DNA polymerase adds nucleotides to the new strand, proofreads the strand, and fixes any mistakes.
Energy for DNA replication comes from the hydrolysis of two phosphate groups from nucleotide triphosphate.
DNA helicase unwinds and separates the double helix.
DNA ligase seals the sugar/phosphate backbone of the nucleotide chain.
The leading strand is synthesized continuously, while the lagging strand is synthesized discontinuously in short fragments called Okazaki fragments.
DNA polymerase adds nucleotides in sections, removes RNA primers, and DNA ligase seals the Okazaki fragments.

Protein Synthesis

Protein synthesis involves two steps:
- Transcription: DNA to mRNA
- Translation: mRNA to protein
Prokaryotic protein synthesis can perform simultaneous transcription and translation.
mRNA carries the genetic code from DNA to ribosomes.
tRNA transports amino acids to the ribosome during protein synthesis.
Amino acids assemble at the ribosome to form proteins.
A codon is a three-base mRNA sequence that encodes a specific amino acid.
Anticodon is the complimentary tRNA sequence to the mRNA codon sequence.
There are three types of codons: start codons, stop codons, and amino acid-specific codons.

Translation

tRNA binds to mRNA at the ribosome and brings the correct amino acid to the growing polypeptide chain.
Ribosomes are composed of ribosomal RNA (rRNA) and protein. They have two subunits:
- Small subunit contains the P-site
- Large subunit contains the E and A sites
Ribosomes have three tRNA binding sites:
- E-site (Exit site)
- P-site (Primary site)
- A-site (Addition site)
Translation proceeds in three steps:
- Initiation: The small ribosome subunit binds to the mRNA, the tRNA with the first amino acid binds to the P-site, and the large subunit binds.
- Elongation: The polypeptide chain grows one amino acid at a time.
- Termination: The ribosome reaches a stop codon, and the polypeptide is released.
Translation involves a complex interplay of different components, including mRNA, tRNA, ribosomes, and amino acids.

Operons

Operons are a group of genes that are transcribed together.
The lac operon in E. coli is an inducible operon, meaning that the genes are not transcribed unless an inducer is present.
Lactose acts as an inducer for the lac operon, binding to the repressor protein and preventing it from binding to the operator.

Mutations

A mutation is a permanent alteration in an organism’s DNA.
Mutations can be caused by DNA replication errors or mutagens.
Mutations have three potential results:
- Harmful — reduces survival rate
- Neutral — no effect
- Beneficial — increases survival rate (adaptive)
Two main types of mutations are single-base substitution and frameshift.
Point mutation is a single-base substitution, resulting in a faulty codon.
Addition mutations insert an extra base, disrupting all downstream codons.
Deletion mutations, remove a base, disrupting all downstream codons.
Missense mutations result in a change in an amino acid.
Nonsense mutations result in a stop codon.

Bacterial Gene Transfer

Horizontal gene transfer is the transfer of genetic material between organisms that are not related by descent.
Vertical gene transfer is the transmission of genetic material from parent to offspring.
Three types of horizontal gene transfer:
- Transformation: uptake of free DNA from the environment.
- Transduction: transfer of DNA via a bacteriophage.
- Conjugation: transfer of DNA via direct contact between bacteria.

Plasmids

Plasmids are small, circular DNA molecules that are separate from the chromosomal DNA.
There are three types of plasmids:
- Resistance plasmids: carry genes for antibiotic resistance.
- Virulence plasmids: carry genes that make bacteria pathogenic.
- Fertility plasmids: called F-plasmids; allow the transfer of DNA via conjugation.

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Test your understanding of DNA replication processes with this quiz. It covers the components involved, the direction of synthesis, and the enzymes responsible for the unwinding and synthesis of DNA strands. Dive into the details to evaluate your knowledge of this essential biological process.