Biology Chapter 14: Gene to Protein

Questions and Answers

What is a polyribosome?

A group of several ribosomes attached to, and translating, the same messenger RNA molecule.

What are some of the things that will result in a final-form functional protein?

Modifications such as protein folding, chemical modification of amino acids, enzymatic removal or rearrangement of amino acids, or the formation of quaternary-level proteins.

Describe at least three types of post-translational modifications.

Chemical modification of amino acids. 2. Enzymes may remove amino acids from the amino end of the polypeptide. 3. Polypeptides may come together to form a protein with quaternary structure.

How are proteins targeted for the ER?

Polypeptide synthesis begins on a free ribosome in the cytosol, an SRP binds to a receptor protein in the ER membrane, and after the polypeptide synthesis resumes, it translocates across the membrane where the signal peptide is cleaved. Signup and view all the answers

Define a mutation in terms of molecular genetics.

A change in the nucleotide sequence of an organism's DNA or in the DNA or RNA of a virus. Signup and view all the answers

Define point mutations.

A change in a single nucleotide pair of a gene. Signup and view all the answers

What are frameshift mutations?

Mutations occurring when nucleotides are inserted in or deleted from a gene, resulting in an improper grouping of subsequent nucleotides into codons. Signup and view all the answers

What is the difference between a nonsense and missense mutation?

A nonsense mutation changes an amino acid codon to a stop codon, resulting in a nonfunctional protein, while a missense mutation substitutes one amino acid for another. Signup and view all the answers

How can a nucleotide-pair substitution result in a silent mutation?

It may change one codon into another that codes for the same amino acid, having no observable effect on the phenotype. Signup and view all the answers

What are the two categories of mutagens?

Physical and chemical. Signup and view all the answers

Describe the action of different types of chemical mutagens.

<ol> <li>Chemicals similar to normal nucleotides that pair incorrectly. 2. Chemicals that insert themselves into DNA and distort it. 3. Chemicals that cause changes in base pairing properties.</li> </ol> Signup and view all the answers

Describe two important ways in which bacterial and eukaryotic gene expression differ.

<ol> <li>Transcription termination differs. 2. Bacterial cells can simultaneously transcribe and translate genes, while eukaryotic cells separate these processes.</li> </ol> Signup and view all the answers

What is a gene?

A region of DNA that can be expressed to produce a final functional product that is either a polypeptide or an RNA molecule. Signup and view all the answers

What is gene expression?

Gene expression is the process by which information encoded in DNA directs the synthesis of proteins or RNAs that function as RNAs. Signup and view all the answers

What situation did Archibald Garrod suggest caused 'inborn errors of metabolism'?

A person's inability to make a particular enzyme. Signup and view all the answers

Describe one example Garrod used to illustrate his hypothesis.

Garrod used the hereditary condition called alkaptonuria as an example. Signup and view all the answers

State the hypothesis formulated by George Beadle while studying eye color mutations in Drosophila.

The hypothesis stated that each mutation affecting eye color blocks pigment synthesis at a specific step. Signup and view all the answers

What strategy did Beadle and Tatum adopt to test their hypothesis?

They bombarded the bread mold Neurospora with X-rays and looked for mutants that differed in nutritional needs. Signup and view all the answers

Which organism did Beadle and Tatum use in their research?

Neurospora. Signup and view all the answers

How were Neurospora spores treated to increase the mutation rate?

Neurospora spores were treated with X-rays. Signup and view all the answers

Cite two significant findings that resulted from the research of Beadle and Tatum.

<ol> <li>Metabolic defects are linked to defective genes. 2. Support for the one gene-one enzyme hypothesis.</li> </ol> Signup and view all the answers

What revision of detail did the one gene-one enzyme hypothesis undergo?

The hypothesis was revised to the one gene-one polypeptide hypothesis. Signup and view all the answers

Find three ways in which RNA differs from DNA.

<ol> <li>RNA contains ribose instead of deoxyribose. 2. RNA has uracil instead of thymine. 3. RNA is usually single-stranded while DNA is double-stranded.</li> </ol> Signup and view all the answers

What are the monomers of DNA and RNA? Of proteins?

The monomers of DNA and RNA are nucleotides, and the monomers of proteins are amino acids. Signup and view all the answers

Define transcription.

Transcription is the synthesis of RNA using a DNA template. Signup and view all the answers

Define translation.

Translation is the synthesis of a polypeptide using the genetic information encoded in an mRNA molecule. Signup and view all the answers

What is the primary transcript in eukaryotes?

Primary transcript. Signup and view all the answers

Write the central dogma of molecular genetics.

DNA to RNA to protein. Signup and view all the answers

How many nucleotide bases are there? How many amino acids?

4 nucleotide bases; 20 amino acids. Signup and view all the answers

How many nucleotides are required to code for these 20 amino acids?

3 nucleotides. Signup and view all the answers

How many unique triplets exist in the genetic code?

64 unique triplets. Signup and view all the answers

What is the coding strand of DNA called when transcribing to mRNA?

Template strand. Signup and view all the answers

Assemble the complementary mRNA strand from the DNA template: 3'A C G A C C A G T A A A 5'.

5' U G C U G G U C A U U U 3'. Signup and view all the answers

How many codons are in the mRNA strand above? Label one codon.

4 codons. Signup and view all the answers

Describe Nirenberg's experiment in which he identified the first codon.

Nirenberg synthesized an artificial mRNA by linking identical RNA nucleotides containing uracil. Signup and view all the answers

What was the first codon-amino acid pair to be identified?

UUU (poly-U)-phenylalanine. Signup and view all the answers

Of the 64 possible codons, how many code for amino acids?

61 codons. Signup and view all the answers

What event is coded for by UAA, UAG, and UGA?

Stop. Signup and view all the answers

What is the start codon?

AUG. Signup and view all the answers

Why is the genetic code said to be redundant but not ambiguous?

More than one codon may specify a particular amino acid, but no codon specifies any other amino acid. Signup and view all the answers

Explain the concept of reading frame.

On an mRNA, the reading frame is the triplet grouping of ribonucleotides used during polypeptide synthesis. Signup and view all the answers

Name the enzyme that uses the DNA template strand to transcribe a new mRNA strand.

RNA polymerase. Signup and view all the answers

Which enzyme does not require a primer to begin synthesis?

RNA polymerase. Signup and view all the answers

What is a transcription unit?

A transcription unit is a region of DNA that is transcribed into RNA. Signup and view all the answers

Name the three stages of transcription and briefly describe each stage.

<ol> <li>Initiation 2. Elongation 3. Termination.</li> </ol> Signup and view all the answers

List three important facts about the promoter.

<ol> <li>It includes the transcription start point. 2. It typically extends upstream from the start point. 3. RNA polymerase binds in a precise location and orientation.</li> </ol> Signup and view all the answers

What is the TATA box?

The TATA box is a DNA sequence in eukaryotic promoters crucial for initiation. Signup and view all the answers

What comprises a transcription initiation complex?

The completed assembly of transcription factors and RNA polymerase bound to a promoter. Signup and view all the answers

What happens at the 5' end of mRNA processing?

The 5' end receives a 5' cap, a modified guanine nucleotide. Signup and view all the answers

What happens at the 3' end of mRNA processing?

The 3' end receives a poly-A tail, adding 50-250 adenine nucleotides. Signup and view all the answers

What are three important functions of the 5' cap and poly-A tail?

<ol> <li>Facilitate mRNA export from the nucleus. 2. Protect mRNA from degradation. 3. Help ribosomes attach to the mRNA.</li> </ol> Signup and view all the answers

Distinguish between introns and exons.

Introns are noncoding segments that are removed, and exons are coding segments that are expressed. Signup and view all the answers

What are snRNPs?

snRNPs are small nuclear ribonucleoproteins made of RNA and protein. Signup and view all the answers

What type is the RNA in a snRNP?

Small nuclear RNA. Signup and view all the answers

How do spliceosomes work?

The spliceosome interacts with intron sites, releasing the intron and joining two exons. Signup and view all the answers

What is a ribozyme?

An RNA molecule that functions as an enzyme. Signup and view all the answers

What idea was rendered obsolete by the discovery of ribozymes?

The idea that all biological catalysts are proteins. Signup and view all the answers

What are three properties of RNA that allow it to function as an enzyme?

<ol> <li>RNA's single-stranded structure allows it to form specific three-dimensional shapes. 2. Some bases in RNA can participate in catalysis. 3. RNA can hydrogen-bond with other nucleic acids.</li> </ol> Signup and view all the answers

What is the consequence of alternative splicing of identical mRNA transcripts?

The number of different protein products can be much greater than the number of genes. Signup and view all the answers

What are the three types of RNA needed for protein synthesis?

<ol> <li>mRNA - messenger RNA, carries genetic material. 2. tRNA - transfer RNA, delivers amino acids. 3. rRNA - ribosomal RNA, makes up ribosomes.</li> </ol> Signup and view all the answers

What is an anticodon?

A nucleotide triplet at one end of a tRNA molecule that base-pairs with a complementary codon on mRNA. Signup and view all the answers

Transfer RNA has two attachment sites. What binds at each site?

A specific anticodon binds at one end, and a corresponding amino acid binds at the other. Signup and view all the answers

How many different aminoacyl-tRNA synthetases are there?

<ol start="20"> <li></li> </ol> Signup and view all the answers

How does wobble explain why scientists found fewer aminoacyl-tRNA synthetases than expected?

Wobble is flexibility in base-pairing rules, allowing one tRNA to match multiple codons. Signup and view all the answers

Explain the process of a specific amino acid being joined to a tRNA.

Aminoacyl-tRNA synthetase binds the amino acid and ATP, then attaches the amino acid to tRNA. Signup and view all the answers

Describe the structure of a eukaryotic ribosome.

A ribosome consists of a large subunit and a small subunit, made of proteins and rRNA. Signup and view all the answers

How does a prokaryotic ribosome differ from a eukaryotic ribosome?

Eukaryotic ribosomes are larger and differ in molecular composition. Signup and view all the answers

Explain the functions of the A, P, and E sites on a ribosome.

The A site holds the tRNA with the next amino acid; the P site holds the growing polypeptide; the E site is where discharged tRNA exits. Signup and view all the answers

What are the three stages of translation?

<ol> <li>Initiation 2. Elongation 3. Termination.</li> </ol> Signup and view all the answers

Summarize the events of translation initiation.

The small ribosomal subunit binds to mRNA, and the initiator tRNA carrying Met pairs with the start codon. Signup and view all the answers

What is always the first amino acid in the new polypeptide?

Methionine. Signup and view all the answers

Summarize the events of elongation during translation.

tRNA in the A site pairs with mRNA codon, peptide bonds form, and tRNA moves along the ribosome. Signup and view all the answers

What is a release factor?

A release factor is a protein that binds to the stop codon in the A site, triggering termination. Signup and view all the answers

What is a polyribosome?

A polyribosome is a cluster of ribosomes translating the same mRNA simultaneously. Signup and view all the answers

Study Notes

Gene Expression and Protein Synthesis

Gene expression involves synthesizing proteins or functional RNAs from DNA information.
Archibald Garrod linked "inborn errors of metabolism" to a person's inability to produce specific enzymes.
Alkaptonuria is a condition illustrating Garrod's hypothesis, leading to black urine due to alkapton accumulation.

Beadle and Tatum's Research

George Beadle hypothesized that eye color mutations in Drosophila inhibit pigment synthesis by blocking enzyme production.
Beadle and Tatum used Neurospora to identify mutants with altered nutritional needs after bombarding it with X-rays.

Organisms and Mutations

Wild-type Neurospora can grow on minimal media, allowing the identification of mutants unable to synthesize essential molecules.
X-ray treatment increased mutation rates in Neurospora spores.
Significant findings from Beadle and Tatum included connections between metabolic defects and defective genes, supporting the one gene-one enzyme hypothesis, later revised to one gene-one polypeptide due to protein structure complexities.

RNA vs. DNA

RNA differs from DNA: ribose sugar vs. deoxyribose, uracil vs. thymine, and typically single-stranded vs. double-stranded.
Monomers of nucleic acids are nucleotides; proteins are comprised of amino acids.

Transcription and Translation Processes

Transcription creates RNA from a DNA template; translation synthesizes polypeptides from mRNA.
Transcription occurs in the nucleus, while translation occurs in the cytoplasm.
Pre-mRNA in eukaryotes is known as the primary transcript.
The central dogma of genetics is DNA to RNA to protein.

Codons and Genetic Code

Four nucleotide bases exist but code for 20 amino acids.
It takes three nucleotides to code for each amino acid, resulting in 64 unique triplets (61 code for amino acids, 3 serve as stop signals).
The start codon is AUG, while UAA, UAG, and UGA are stop codons.
The genetic code is redundant yet unambiguous.

Ribosomes and Protein Synthesis

Ribosomes consist of large and small subunits made of rRNA and proteins.
Prokaryotic ribosomes are smaller and structurally different from eukaryotic, allowing antibiotics to target bacterial synthesis without affecting eukaryotic cells.
The ribosome has A, P, and E sites for tRNA attachment: A site for new tRNA, P site for growing polypeptide, E site for discharged tRNA.

Stages of Translation

Translation involves initiation, elongation, and termination.
Initiation begins with the small ribosomal subunit binding to mRNA, with the initiator tRNA carrying methionine (Met) binding to the start codon AUG.
Elongation involves tRNA base-pairing with mRNA codons, forming peptide bonds between amino acids.
Termination occurs when a release factor binds to the stop codon, releasing the completed polypeptide.

Post-Translational Modifications

Proteins undergo modifications post-translation, including folding, chemical modifications, and assembly into quaternary structures.
Types of modifications involve chemical alterations, removal of initial amino acids, and subunit assembly for multi-chain proteins like hemoglobin.

Splicing and mRNA Processing

RNA processing involves adding a 5' cap and a poly-A tail, promoting mRNA stability and ribosome attachment.
Introns are noncoding sequences, while exons are coding sequences that are expressed.
snRNPs and spliceosomes play crucial roles in recognizing splice sites and removing introns.
Ribozymes are RNA molecules that can catalyze reactions, showcasing that not all biological catalysts are proteins.

Mutations

A mutation is a change in nucleotide sequence in DNA or RNA.
Point mutations involve a single nucleotide change, while frameshift mutations insert or delete nucleotides, altering the reading frame. ### Frameshift Mutation
A frameshift mutation occurs due to insertion or deletion of nucleotides in a gene.
The number of nucleotides involved is not a multiple of three.
This mutation causes improper grouping of the remaining nucleotides into codons, impacting protein synthesis.

Nonsense vs. Missense Mutation

Nonsense mutation converts an amino acid codon into a stop codon, leading to a truncated and often nonfunctional protein.
Missense mutation results from a nucleotide-pair substitution, resulting in a codon that codes for a different amino acid.

Silent Mutation Mechanism

Nucleotide-pair substitution can create a codon that translates to the same amino acid.
Silent mutations do not produce any observable changes in phenotype.

Categories of Mutagens

Mutagens are classified into two main types: physical and chemical.

Action of Chemical Mutagens

Some chemical mutagens resemble normal DNA nucleotides but mispair during DNA replication.
Certain chemicals integrate into DNA, distorting the double helix structure and hindering replication.
Additional chemicals can chemically alter bases, changing their pairing properties and potentially leading to mutations.

Differences in Gene Expression: Bacteria vs. Eukaryotes

Transcription termination varies between bacterial and eukaryotic cells.
Bacteria can concurrently transcribe and translate genes due to the absence of a nucleus, allowing swift protein function.
Eukaryotic gene expression is separated by the nuclear envelope, which segregates transcription from translation and facilitates extensive RNA processing, enhancing cellular regulation.

Definition of a Gene

A gene is defined as a DNA region capable of being expressed to yield either a polypeptide or an RNA molecule, expanding on the previous notion that one gene codes solely for one polypeptide.

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Description

This quiz focuses on key concepts from Chapter 14 of biology regarding gene expression and its role in protein synthesis. Test your knowledge on important terms and theories presented in this chapter, including insights from Archibald Garrod on metabolism. Prepare to explore the mechanisms that bridge DNA and functional proteins.