Nucleic Acids II
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What is the purpose of the start codon AUG in protein synthesis?

  • It codes for Glycine
  • It initiates the translation of all proteins
  • It terminates protein synthesis
  • It codes for Methionine (correct)

The genetic code is nonoverlapping, meaning that codons overlap with one another.

False (B)

How many codons are responsible for terminating protein synthesis?

3

In eukaryotic ribosomes, the two subunits are ____ and ____.

<p>60S and 40S</p> Signup and view all the answers

Match the components required for protein synthesis with their roles:

<p>Amino acids = Building blocks of proteins tRNA = Transfers specific amino acids to the ribosome mRNA = Carries genetic information from DNA Ribosomes = Sites of protein synthesis</p> Signup and view all the answers

Which of the following codons are termination codons recognized by releasing factors?

<p>UGA (B), UAA (C)</p> Signup and view all the answers

Antibiotics can only affect eukaryotic ribosomes due to their size.

<p>False (B)</p> Signup and view all the answers

What is the function of releasing factors in protein synthesis?

<p>To promote the hydrolysis of the bond between peptide and tRNA.</p> Signup and view all the answers

The structure that consists of one mRNA and multiple ribosomes is called a __________.

<p>polysome</p> Signup and view all the answers

Match each antibiotic with its corresponding action:

<p>Streptomycin = Distorts ribosome structure Tetracycline = Prevents tRNA recognition of codons Chloramphenicol = Inhibits peptidyl transferase Puromycin = Incorporates into growing peptide chain</p> Signup and view all the answers

What is the role of the P site in protein synthesis?

<p>Carry the growing polypeptide chain (B)</p> Signup and view all the answers

The A site is responsible for the assembly of components before peptide bond formation.

<p>False (B)</p> Signup and view all the answers

What is the significance of the initiator tRNA?

<p>It carries methionine and recognizes the start codon AUG.</p> Signup and view all the answers

Protein synthesis translates the codons on mRNA into _____ that constitute the protein.

<p>amino acids</p> Signup and view all the answers

Match the following steps of protein synthesis with their descriptions:

<p>Initiation = Assembly of components before peptide bond formation Elongation = Addition of amino acids to the growing polypeptide chain Termination = Final step when a termination codon is reached Translocation = Movement of ribosomes along the mRNA</p> Signup and view all the answers

During which step of protein synthesis does peptidyl transferase enzyme act?

<p>Elongation (D)</p> Signup and view all the answers

The ribosomes move three bases toward the 5’ end of mRNA during translocation.

<p>False (B)</p> Signup and view all the answers

What happens during the termination step of protein synthesis?

<p>The ribosome encounters a termination codon in the A site and stops translation.</p> Signup and view all the answers

What is released when a new nucleotide is added to the growing RNA chain?

<p>Pyrophosphate (PPi) (B)</p> Signup and view all the answers

The presence of palindromes in the termination region on DNA is irrelevant for RNA polymerase.

<p>False (B)</p> Signup and view all the answers

What is the role of the 7-methylguanosine triphosphate in mRNA processing?

<p>It facilitates the initiation of translation and protects the 5' end from exonucleases.</p> Signup and view all the answers

The process of adding a chain of 40-250 adenine nucleotides to the 3' end of mRNA is known as __________.

<p>polyadenylation</p> Signup and view all the answers

Match the following steps of mRNA post-transcriptional modifications with their descriptions:

<p>5' Capping = Addition of 7-methylguanosine to the 5' end Poly-A tail = Addition of a chain of adenine nucleotides to the 3' end Splicing = Removal of introns and ligation of exons</p> Signup and view all the answers

What is the function of the Rho factor in RNA termination?

<p>To bind with RNA polymerase and cause termination (B)</p> Signup and view all the answers

Codons are the sequences of 4 nucleotide bases on mRNA.

<p>False (B)</p> Signup and view all the answers

What is the genetic code?

<p>The dictionary that relates the sequence of bases in DNA and mRNA to a sequence of amino acids in a protein.</p> Signup and view all the answers

What is the primary role of mRNA in a cell?

<p>To carry genetic information from DNA to the cytosol for protein synthesis (D)</p> Signup and view all the answers

Ribosomal RNA (rRNA) makes up 15% of the total RNA in the cell.

<p>False (B)</p> Signup and view all the answers

What are the three main steps of transcription?

<p>Initiation, Elongation, Termination</p> Signup and view all the answers

The ___________ region in prokaryotic cells is recognized by the RNA polymerase during initiation.

<p>promoter</p> Signup and view all the answers

Match the following RNA types with their primary functions:

<p>mRNA = Carries genetic information for protein synthesis tRNA = Transfers specific amino acids to the ribosome rRNA = Makes up the structural framework of ribosomes small RNA = Performs regulatory functions in the cell</p> Signup and view all the answers

Which RNA polymerase in eukaryotic cells is responsible for synthesizing mRNA?

<p>RNA polymerase II (B)</p> Signup and view all the answers

All types of RNA in prokaryotes are synthesized by multiple RNA polymerases.

<p>False (B)</p> Signup and view all the answers

How many base pairs are found between the Pribnow box and the second nucleotide sequence in prokaryotic promoters?

<p>19</p> Signup and view all the answers

The building blocks of RNA are ribonucleotides, which consist of a nitrogenous base, sugar __________, and phosphate.

<p>ribose</p> Signup and view all the answers

Which of the following statements regarding the anticodon region of tRNA is correct?

<p>It is complementary to the codons on mRNA. (C)</p> Signup and view all the answers

Flashcards

Specificity of Genetic Code

A specific codon always codes for only one amino acid.

Degeneracy of Genetic Code

Multiple codons can code for the same amino acid.

Non-overlapping Genetic Code

The genetic code is read continuously from a fixed starting point, three bases at a time.

Universality of Genetic Code

The genetic code is mostly universal across all living organisms, with a few exceptions.

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Translation (Protein Synthesis)

The process of protein synthesis where mRNA codons are recognized by tRNA anticodons, leading to the assembly of a polypeptide chain.

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Stop codons

These are UAA, UAG, and UGA and signal the end of protein synthesis.

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Releasing factors

Proteins that bind to stop codons in the A site of the ribosome, triggering the release of the newly synthesized polypeptide chain.

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Polysome

A complex of multiple ribosomes translating the same mRNA molecule simultaneously, enabling efficient protein production.

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Antibiotics

These molecules interfere with bacterial protein synthesis, targeting specific ribosomal components.

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Diphtheria toxin

A toxin that halts translation by inactivating eEF-2, a crucial protein responsible for translocation during protein synthesis.

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Codon

A sequence of three nucleotides on mRNA that specifies a particular amino acid or a start or stop signal during protein synthesis.

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Termination Region

A region on the DNA template that signals the end of transcription, leading to the release of the newly synthesized RNA molecule.

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Palindrome

A DNA sequence that reads the same backwards and forwards on opposite strands. It often leads to the formation of hairpin structures in RNA that can trigger termination of transcription.

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Rho Factor

A protein that binds to the RNA polymerase during transcription and helps to terminate transcription in rho-dependent termination.

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mRNA Post-Transcriptional Modifications

The process of modifying a pre-mRNA molecule into a mature mRNA molecule. This includes adding a 5' cap, a poly-A tail, and removing introns.

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5' Cap

A modified guanine nucleotide that is added to the 5' end of a pre-mRNA molecule. Helps protect the mRNA from degradation and facilitates translation.

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Poly-A Tail

A string of adenine nucleotides added to the 3' end of a pre-mRNA molecule. Protects the mRNA from degradation and helps with translation.

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Introns

Segments of RNA that are removed from the pre-mRNA molecule during splicing. They are not translated into protein.

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Transcription

The process of copying genetic information from DNA to mRNA, creating a 'working copy' for protein synthesis.

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Translation

The process of creating proteins from mRNA instructions, using the genetic code to build amino acid chains.

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Messenger RNA (mRNA)

A single-stranded polynucleotide molecule responsible for carrying genetic information from DNA to ribosomes.

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Transfer RNA (tRNA)

A small RNA molecule that acts as an adaptor, bringing specific amino acids to ribosomes during protein synthesis.

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Ribosomal RNA (rRNA)

A type of RNA that forms the structural and functional core of ribosomes, the protein synthesis machinery.

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Promoter Region

A specific DNA sequence that signals the RNA polymerase enzyme where to begin transcription.

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Termination Unit

A DNA sequence that signals the RNA polymerase enzyme to stop transcription.

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RNA polymerase

An enzyme responsible for reading DNA and creating RNA during transcription.

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Initiation (Transcription)

The first step of transcription, where RNA polymerase binds to the promoter and unwinds the DNA double helix.

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Elongation (Transcription)

The second step of transcription, where RNA polymerase reads the DNA template and adds RNA nucleotides to build the RNA chain.

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What are the three sites on a ribosome?

The three sites on a ribosome that are involved in protein synthesis: the A site (aminoacyl site) binds incoming aminoacyl-tRNAs, the P site (peptidyl site) holds the tRNA carrying the growing polypeptide chain, and the E site (exit site) releases uncharged tRNAs.

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What is protein synthesis?

Protein synthesis is the process of translating the genetic information encoded in mRNA into a polypeptide chain, which then folds into a functional protein.

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What happens during the initiation phase of protein synthesis?

The initiation phase of protein synthesis involves assembling the ribosome, mRNA, and the initiator tRNA (carrying methionine) at the start codon (AUG).

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What happens during the elongation phase of protein synthesis?

The elongation phase of protein synthesis involves the sequential addition of amino acids to the growing polypeptide chain, guided by the codon-anticodon interaction between mRNA and tRNAs.

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How does the ribosome move during elongation?

In the elongation phase, ribosomes move along the mRNA in a 5' to 3' direction, ensuring that amino acids are added in the correct order to the growing polypeptide chain.

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What happens during the termination phase of protein synthesis?

The termination phase of protein synthesis occurs when the ribosome encounters a stop codon (UAG, UAA, or UGA) on the mRNA, signaling the end of the protein.

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Why is protein synthesis important?

The process of protein synthesis ensures that the genetic information stored in DNA is ultimately used to create functional proteins that perform diverse roles in the cell.

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What is peptidyl transferase?

Peptidyl transferase is an enzyme that catalyzes the formation of peptide bonds between amino acids during protein synthesis.

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Study Notes

Nucleic Acids II

  • Nucleic acids are single-stranded polynucleotides.
  • The central dogma describes the flow of genetic information from DNA to RNA to protein.
  • DNA is the master plan, containing the genetic information of an organism.
  • mRNA is the working copy of DNA, expressing the master plan.
  • Transcription is the process of copying DNA to create mRNA.
  • Translation is the process of converting mRNA into protein.
  • RNA types include mRNA, tRNA, rRNA, and small RNA molecules.
  • mRNA carries genetic information from DNA to the cytoplasm for protein synthesis.
  • mRNA makes up about 5% of the total RNA in a cell.
  • Each three consecutive nucleotides in mRNA form a codon, which codes for a specific amino acid.
  • tRNA is an adaptor molecule carrying amino acids.
  • tRNA makes up about 15% of the total RNA.
  • tRNA has three loops and two free ends.
  • tRNA has an anticodon region that is complementary to codons on mRNA.
  • rRNA is found in association with proteins in ribosomes, serving as sites for protein synthesis.
  • rRNA makes up about 80% of the total RNA.
  • Prokaryotic ribosomes are 70S with subunits 50S and 30S.
  • Eukaryotic ribosomes are 80S with subunits 60S and 40S, differences in ribosomal subunit composition.
  • RNA consists of a nucleotide compound with nitrogenous bases, a ribose sugar, and a phosphate group.
  • RNA's nucleotides are linked by phosphodiester bonds.
  • RNA exists as single strands capable of complex folding.
  • The most common nitrogenous bases in RNA include adenine, guanine, cytosine, and uracil (instead of thymine).

RNA Structure

  • RNA is a polynucleotide, building blocks of nucleotides.
  • A nucleotide is composed of a nitrogenous base, ribose sugar, and monophosphate.
  • Nucleotides are connected via phosphodiester bonds.
  • RNA exists as single strands that can fold into complex structures.

Messenger RNA (mRNA)

  • mRNA is the working copy of the DNA.
  • It carries genetic information from DNA to the cytosol for protein synthesis.
  • It comprises about 5% of total RNA.
  • mRNA codons specify particular amino acids.

Transfer RNA (tRNA)

  • tRNA is a molecule that carries amino acids.
  • tRNA comprises about 15% of total RNA in a cell.
  • tRNA has three loops and two free ends and an anticodon.
  • tRNA's anticodon sequence matches corresponding mRNA codons.

Ribosomal RNA (rRNA)

  • rRNA is found in ribosomes and is essential for protein synthesis.
  • rRNA makes up the majority (about 80%) of total RNA in a cell.
  • Prokaryotic rRNA has three types (5S, 23S, and 16S)
  • Eukaryotic rRNA has four types (5S, 5.8S, 28S, and 18S)
  • S refers to Svedberg units, a measure of sedimentation rate.

RNA Transcription

  • mRNA synthesis is known as RNA transcription.
  • Transcription requires a DNA template, ribonucleotides (phosphates A, G, C, U) and RNA polymerase.
  • DNA template consists of a promoter region, a transcription unit, and a termination unit.
  • Promoter region initiates transcription.
  • Transcription unit is the transcribed region.
  • Termination unit ends transcription.

Promoter Region

  • Prokaryotic promoters have a Pribnow box (-10 region) and a -35 region.
  • Eukaryotic promoters have a TATA box and a CAAT box.

Prokaryotic RNA Polymerase

  • One type of RNA polymerase synthesizes all types of RNA molecules.
  • RNA polymerase enzyme responsible for synthesis of RNA molecules.

Eukaryotic RNA Polymerases

  • Eukaryotes have three types of RNA polymerases: I, II, and III.
  • RNA polymerase I synthesizes rRNA.
  • RNA polymerase II synthesizes mRNA and has a promoter region.
  • RNA polymerase III synthesizes tRNA and small RNA.

Steps of Transcription

  • Initiation, elongation, and termination.

Steps of protein synthesis

  • Initiation, elongation, and termination.

Initiation

  • Ribosomes, mRNA, aminoacyl-tRNA specified by the first codon (AUG for methionine), and initiation factors are involved.
  • The initiator tRNA (carrying methionine) enters the P site. First codon recognized by a special initiator tRNA.

Elongation

  • Amino acids are added to the growing polypeptide chain.
  • The aminoacyl-tRNA whose codon appears next on mRNA will be delivered to the A-site.
  • The carboxyl group of aminoacyl-tRNA in the P site is transferred to the amino group of the new aminoacyl-tRNA in the A site.
  • Ribosomes move three bases along the mRNA.
  • The uncharged tRNA leaves the ribosome.

Termination

  • The ribosome reaches a termination codon (UAA, UAG, or UGA).
  • Release factors recognize termination codons.
  • The bond between peptide and tRNA is hydrolyzed.
  • The polypeptide is released.
  • Ribosome subunits dissociate.

Polysomes

  • Multiple ribosomes can translate the same mRNA simultaneously.
  • This complex of mRNA and ribosomes is called a polysome.

Inhibition of Protein Synthesis

  • Antibiotics target bacterial ribosomes (70S), which are different from eukaryotic ribosomes (80S).

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