Bio- Chapter 12- Transcription and Translation

What happened to Gregor Mendel's work in the early 1900s?

Mendel's work on genetics, originally published in 1865, was rediscovered and finally understood in the early 1900s.

Who was Archibald Garrod, and what did he study?

Archibald Garrod was a British physician who studied the inheritance of a disease called Alkaptonuria.

What connection did Archibald Garrod propose in 1908?

He proposed that genes are connected to the production of enzymes.

What did biochemists understand about metabolic pathways by 1908?

Metabolic pathways consist of a series of enzymes, with each enzyme converting one chemical into another.

How did Garrod connect genes to metabolic pathways?

He applied Mendel's theory of inheritance to the breakdown of Phenylalanine and the disease Alkaptonuria. He proposed that defective genes could prevent normal enzyme production.

How did Garrod believe Alkaptonuria was inherited?

He believed Alkaptonuria occurred when an individual inherited defective recessive genes from both parents.

What was Garrod's major contribution to genetics?

He was the first to connect genes with enzyme production, showing that inherited genetic defects can affect metabolic pathways.

What did Garrod mean by "Inborn Errors of Metabolism"?

He used this term to describe inherited defects that interfere with normal metabolism because of defective genes.

What field did Garrod's research help establish?

Human Genetics, also called Medical Genetics.

Who were Beadle and Tatum, and what did they investigate?

Beadle and Tatum were scientists who studied the nutritional needs of a mold called Neurospora in 1941.

How did Beadle and Tatum produce mutations in Neurospora?

They exposed mold spores to X-rays to produce mutations.

What happened after Beadle and Tatum exposed Neurospora spores to X-rays?

They isolated mutant strains of mold that could no longer produce certain nutrients.

What were Beadle and Tatum investigating with their mutant mold strains?

They were investigating the inheritance and genetics of the mutant strains to understand how genes affect an organism's ability to produce nutrients.

What was known about the metabolic pathway for Arginine production?

Arginine production was controlled by three different enzymes, with each enzyme responsible for a different step in the pathway.

What did Beadle and Tatum discover about their Neurospora strains?

They had several mutant strains of Neurospora that could not produce Arginine.

Why did different Neurospora strains fail to produce Arginine?

Different strains had mutations in different genes. Each mutation disrupted a different step in the Arginine production pathway.

What did Beadle and Tatum originally propose based on their experiments?

They proposed the One Gene–One Enzyme Theory, which stated that each gene controls the production of a separate enzyme.

What does the One Gene–One Enzyme Theory mean?

Each gene provides the instructions for producing a particular enzyme that performs a specific function in a metabolic pathway.

Why was the One Gene–One Enzyme Theory modified?

Scientists discovered that not all genes code for enzymes, and some enzymes are made of multiple polypeptides produced by different genes.

Do all genes code for enzymes?

No. Genes can code for other types of proteins and functional RNA molecules, not just enzymes.

Why don't all enzymes follow the One Gene–One Enzyme Theory?

Some enzymes contain multiple polypeptides. Each polypeptide is produced by a different gene, and the polypeptides combine to form one complete enzyme.

What is the One Gene–One Polypeptide Theory?

It is the modified version of the One Gene–One Enzyme Theory. It states that each gene codes for one polypeptide rather than necessarily coding for an entire enzyme.

What occurs when one gene's RNA is spliced in different ways to produce multiple versions of a protein?

alternative splicing

How can one gene produce multiple proteins?

Through alternative splicing, different combinations of RNA segments are joined together, allowing one gene to produce multiple protein versions.

How many human genes are estimated to produce approximately 500,000+ proteins?

Approximately 20,000 human genes can produce 500,000+ proteins, partly because of alternative splicing.

What is the Central Dogma of Biology?

It describes the flow of genetic information within cells: DNA → RNA → Protein.

What are the three main stages of information flow in the Central Dogma?

DNA stores genetic information.

Transcription copies DNA into RNA.

Translation uses RNA to make proteins.

What is the process of using DNA as a template to produce RNA. Also called DNA-directed RNA synthesis?

Transcription

What enzyme is primarily responsible for transcription?

RNA Polymerase. It builds an RNA molecule using DNA as a template.

What is a specific region of DNA where RNA Polymerase attaches to begin transcription of a gene?

Promoter

What is the role of RNA Polymerase binding to a promoter?

It helps identify where transcription begins so the correct gene can be transcribed.

Which DNA strand is used during transcription?

Only the template strand is used as the guide to make RNA.

Does transcription occur across the entire DNA molecule at once?

No. Transcription occurs one gene at a time.

What happens when RNA Polymerase attaches to the promoter?

RNA Polymerase attaches to the promoter and unwinds (denatures) the DNA, separating the two strands.

What does it mean when DNA is denatured during transcription?

The DNA double helix unwinds, and its two strands separate so RNA Polymerase can access the template strand.

What helps RNA Polymerase attach to DNA in eukaryotes?

Special proteins called Initiation Factors and Transcription Factors help RNA Polymerase attach to the promoter.

What are proteins that help regulate transcription and assist RNA Polymerase in recognizing and attaching to the promoter?

Transcription factors

What is the building blocks used to make RNA during transcription?

Ribonucleoside Triphosphates

How do Ribonucleoside Triphosphates line up during transcription?

They line up opposite their complementary bases on the DNA template strand.

What is the role of RNA Polymerase during RNA synthesis?

RNA Polymerase connects the Ribonucleoside Triphosphates together to form an RNA strand.

In which direction does RNA Polymerase build RNA?

RNA is always synthesized in the 5′ → 3′ direction.

What are the precursors (building blocks) used to make RNA during transcription?

Ribonucleoside Triphosphates

What happens to Ribonucleoside Triphosphates during RNA synthesis?

Pyrophosphate is removed, allowing the nucleotide to be added to the growing RNA chain.

Where is a new nucleotide added to the growing RNA strand?

To the 3′ end of the growing RNA chain.

What is the role of pyrophosphate removal during transcription?

It releases energy that helps drive the joining of nucleotides to form the RNA strand.

What is the stage when transcription stops and RNA Polymerase stops producing the RNA strand?

termination

Does transcription termination happen the same way for all RNAs?

No. Termination occurs in different ways depending on the type of RNA.

What is the initial RNA molecule produced during transcription before it undergoes processing?

pre-RNA

Is the primary transcript the finished RNA product?

No. The primary transcript (pre-RNA) must undergo additional processing before becoming mature, functional RNA.

What is messenger RNA carries genetic instructions from DNA to the ribosome, where proteins are made?

mRNA

What is ribosomal RNA that is a component of ribosomes and helps make up their structure?

rRNA

What carries (escorts) amino acids to the ribosome during protein synthesis!?

tRNA

How are mRNA, rRNA, and tRNA produced?

All three types are produced through transcription using DNA as a template.

Within a single chromosome, can different genes use different DNA strands as the template strand?

Yes. Different genes can use different strands of the double-stranded DNA as their template strand during transcription.

What are changes made to RNA molecules after transcription is completed. These modifications help prepare RNA for its final function?

post-transcriptional modifications

Are post-transcriptional modifications limited to mRNA?

No. All three main types of RNA (mRNA, rRNA, and tRNA) undergo post-transcriptional modifications.

What is the purpose of studying post-transcriptional modifications?

To understand the different ways RNA is modified after it is made

Which type of RNA receives the 5′ 7-methylguanosine cap?

mRNA only. The 5′ 7-methylguanosine cap is added to the 5′ end of mRNA during post-transcriptional processing.

Which type of RNA receives a Poly-A tail?

mRNA only. A Poly-A tail is added to the 3′ end of mRNA after transcription.

What are the functions of the Poly-A tail?

Helps mRNA leave the nucleus and enter the cytosol.

What is the process of removing introns (intervening, noncoding regions) from an RNA transcript?

RNA splicing

What are sections of RNA that are removed during splicing rather than retained in the final RNA product?

Introns

What are complexes made of RNA and proteins that carry out RNA splicing by removing introns?

spliceosomes

Can splicing occur in all types of RNA?

Yes. According to the lecture, intron removal can occur in any type of RNA.

How does RNA splicing affect the length of an RNA transcript?

Removing introns makes the RNA transcript much shorter than the corresponding DNA gene.

What is a process where different combinations of exons are included in the final mRNA, allowing one gene to produce different mRNA molecules?

alternative splicing

Are all exons always included in the final mRNA during alternative splicing?

No. Different exons can be included or skipped, creating different combinations of exons.

How can alternative splicing allow one gene to produce different proteins?

Different combinations of exons create different mRNA molecules. These mRNAs can be translated into different proteins in different cells or tissues.

How many human genes produce approximately 500,000+ proteins?

Approximately 20,000 genes can produce over 500,000 proteins, partly because of alternative splicing.

What can happen to a primary/pre-RNA transcript during RNA processing?

The primary transcript can be cut into more than one separate RNA molecule.

Which types of RNA can undergo cleavage of the primary transcript?

All types of RNA can undergo this modification, but it always occurs in rRNA.

What does it mean when a primary RNA transcript is cut into more than one RNA?

One long initial RNA molecule is divided into multiple smaller, separate RNA molecules.

Which types of RNA undergo nucleotide removal from their 5’ or 3’ ends?

All three types: mRNA, rRNA, and tRNA.

What happens during removal of nucleotides from RNA ends?

Extra nucleotides are trimmed from the beginning (5′ end), the end (3′ end), or both ends to produce mature RNA.

What is added to the 3′ end of some tRNA molecules?

The sequence CCA (cytosine, cytosine, adenine) is added if it is not already present.

Which type of RNA receives the CCA sequence?

tRNA only.

What is a process where the nitrogenous bases in an RNA molecule are chemically changed after transcription?

Chemical modification

Which type of RNA undergoes chemical modification of its bases?

tRNA only.

What is a process where one or more nucleotides in an RNA molecule are changed, added, or removed after transcription?

RNA editing

What are the two main types of RNA editing?

Substitution editing

Insertion/deletion editing

What occurs when one nucleotide is chemically changed into another nucleotide?

Substitution editing

What enzyme converts cytidine (C) into uracil (U)?

Cytidine deaminase converts C into U.

What enzyme converts adenosine (A) into inosine (I)?

Adenosine deaminase converts A into inosine (I).

How does the ribosome interpret inosine (I) during translation?

The ribosome reads inosine similarly to guanine (G).

What occurs when nucleotides are added to or removed from an RNA molecule?

Insertion/deletion editing

What are guide RNAs used for during insertion/deletion editing?

Guide RNAs bind to specific RNA molecules and help identify where nucleotides should be added or removed.

Which types of RNA can undergo RNA editing?

All RNA’s

What can happen if RNA editing contains errors?

Errors in RNA editing have been associated with neurological and mental disorders, including schizophrenia.

What are the three types of RNA involved in translation?

mRNA, tRNA, and rRNA.

What is the role of mRNA during translation?

Carries the genetic instructions from DNA to the ribosome, telling it the order of amino acids.

What is the role of tRNA during translation?

Transfers amino acids to the ribosome so they can be joined together to make a protein.

What is the role of rRNA during translation?

rRNA is a structural and functional component of ribosomes, where proteins are made.

What are aminoacyl-tRNA synthetases?

Enzymes that attach the correct amino acid to its corresponding tRNA molecule.

What is the genetic code uses groups of three nucleotide bases to communicate instructions during translation?

Triplet code

What is a sequence of three bases on mRNA that codes for an amino acid or a stop signal?

Codon

How many bases make up one codon?

Three bases

What is the initiation/start codon?

AUG is the start codon that signals where translation begins.

Which amino acid does AUG code for?

Methionine (Met).

What are the three stop codons?

UAA

UAG

UGA

What is the function of stop codons?

They signal the ribosome to stop translation rather than add another amino acid.