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Questions and Answers
Beadle and Tatum's experiment with Neurospora crassa led to which initial hypothesis about the relationship between genes and enzymes?
Beadle and Tatum's experiment with Neurospora crassa led to which initial hypothesis about the relationship between genes and enzymes?
- Multiple genes code for one enzyme.
- Genes directly synthesize amino acids without enzymes.
- One gene codes for one enzyme. (correct)
- One gene codes for multiple enzymes.
The central dogma of molecular biology states that RNA is directly replicated to produce DNA.
The central dogma of molecular biology states that RNA is directly replicated to produce DNA.
False (B)
Which of the following is a key difference between DNA replication and transcription?
Which of the following is a key difference between DNA replication and transcription?
- Replication synthesizes in the 3’→5’ direction, while transcription synthesizes in the 5’→3’ direction.
- Replication copies both DNA strands, while transcription copies only one DNA strand. (correct)
- Replication uses RNA polymerase, while transcription uses DNA polymerase.
- Replication copies only some DNA fragments, while transcription copies the entire DNA molecule.
During transcription, RNA polymerase starts its synthesis next to regions on the DNA called _______.
During transcription, RNA polymerase starts its synthesis next to regions on the DNA called _______.
If a gene sequence is typically given as the coding strand in the 5' to 3' direction, what does this imply about the template strand used for transcription of that gene?
If a gene sequence is typically given as the coding strand in the 5' to 3' direction, what does this imply about the template strand used for transcription of that gene?
What is a gene defined as, in terms of its function?
What is a gene defined as, in terms of its function?
Which class of eukaryotic RNAs is typically NOT processed after transcription?
Which class of eukaryotic RNAs is typically NOT processed after transcription?
What is the significance of alternative splicing in eukaryotic cells?
What is the significance of alternative splicing in eukaryotic cells?
The number of genes in an organism is directly proportional to its complexity.
The number of genes in an organism is directly proportional to its complexity.
Match the enzyme with its function in either DNA replication or transcription:
Match the enzyme with its function in either DNA replication or transcription:
Flashcards
One gene - one enzyme hypothesis
One gene - one enzyme hypothesis
Each gene encodes one enzyme. (Later found to be oversimplified)
Central Dogma
Central Dogma
DNA -> RNA -> Protein. The flow of genetic information in cells.
Replication
Replication
Copying the entire DNA molecule.
Transcription
Transcription
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Coding Strand
Coding Strand
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Template Strand
Template Strand
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Gene
Gene
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Promoters
Promoters
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Alternative Splicing
Alternative Splicing
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One gene yields many polypeptides
One gene yields many polypeptides
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Study Notes
- In 1940 Beadle and Tatum found that a deficiency in an enzyme in Neurospora crassa resulted in the fungi not being able to synthesize an amino acid was inherited.
- They proposed the "one gene → one enzyme hypothesis", which turned out to be incorrect.
- In the 1950s and 60s, Ochoa, Brenner, Jacob, and Meselson determined that RNA was an intermediate molecule in the central dogma.
- The central dogma describes how DNA is transcribed into RNA, which is then translated into protein.
Replication vs Transcription
- Replication copies the complete DNA molecule, while transcription copies only some DNA fragments.
- Replication copies both DNA strands; transcription copies only one of the DNA strands, and it is not always the same strand for a given DNA molecule.
- DNA polymerase is used in Replication; RNA polymerase is used in Transcription.
- DNA polymerase needs a template and a primer, additionally, it uses dNTPs as substrates.
- RNA polymerase needs a template but does not need a primer and uses NTPs as substrates.
- Both replication and transcription synthesize in the 5' → 3' direction.
- Replication starts at origins of replication, whereas transcription starts next to promoters.
Coding Strand
- When only a single strand is given for the sequence of a gene, that sequence is the coding strand in the 5' to 3' direction from left to right.
Promoters
- Promoters are located upstream of the transcribed region.
- The promoter sequences are DNA sequences that have all the information necessary for the synthesis of RNA.
Eukaryotic vs Bacterial cells
- Bacterial and eukaryotic process genes differently.
- Bacterial cells contain DNA and RNA in their cell, along with ribosomes.
- Inside eukaryotic cells the DNA in is the nucleus.
Pre-mRNA Processing
- Pre-mRNA undergoes processing that includes multiple steps.
- Capping occurs adding protection of mRNA molecule and binding of mRNA to ribosomes.
- Cleavage and polyadenylation also occurs.
- Polyadenylation signals are present.
- PAP adds new adenines to the 3' end.
- Poly-A tails help also increase the rate of polyadenylation
Splicing
- Splicing is the removal of introns and joining of exons
- Capping is present.
- All mRNA's are spliced except for histones.
Alternative Splicing
- Alternative splicing results in more than on polypeptide from on gene.
- Alternative splicing results in more proteins from the pre-mRNA and therefore can result in more proteins and more specific functions without increasing the amount of DNA in the genome.
- Genome sequencing of organisms does not correspond with the complexity of an organism.
- Humans have about 20,000-25,000 genes
- Fruit flies have about 14,000 genes
- The alternative splicing mechanisms allows production for more protein.
- Calcitonin/CGRP are alternative splicing patterns.
- Present in neuronal cells as CGRP
- Present in thyroid cells as Calcitonin
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Description
The central dogma outlines the process of DNA transcription into RNA, followed by RNA translation into proteins. Beadle and Tatum's experiment with Neurospora crassa led to the initial one gene → one hypothesis. Key differences exist between replication and transcription regarding strands copied and enzymes used.
