ACTUAL Lecture 1 LMAO

What did Garrod’s 1902 experiment show?

Genes are linked to enzymes and metabolic diseases  

What disease did Garrod study? 

Alkaptonuria (black urine disease)  

What did Garrod propose about affected patients?

They lacked a specific enzyme 

What did Beadle and Tatum discover?

Each gene codes for a specific enzyme  

What is the modern version of their hypothesis?

One gene → one polypeptide (protein)  

How does DNA determine phenotype?

DNA → protein → protein function produces traits  

What is gene expression?

The process by which DNA directs protein synthesis  

What are the two stages of gene expression? 

Transcription and translation  

What is transcription?

DNA → mRNA  

What is translation? 

mRNA → protein  

Where does transcription occur (eukaryotes)?

Nucleus

Where does translation occur?

Cytoplasm (ribosomes)  

What is a codon?

 A 3-nucleotide sequence that codes for one amino acid  

Why are codons needed?

Because 4 nucleotides must code for 20 amino acids  

How many nucleotides are in one codon?

3

What strand is used in transcription?

The template DNA strand  

In what direction is mRNA built?

5’ → 3’  

What replaces thymine (T) in RNA?

Uracil (U)  

What enzyme performs transcription? 

RNA polymerase  

What does RNA polymerase do?

Unwinds DNA and builds mRNA  

What happens in transcription initiation?

RNA polymerase binds promoter and unwinds DNA  

What happens in transcription elongation?

RNA strand is extended as polymerase moves along DNA  

What happens in transcription termination?

mRNA is released and polymerase detaches  

What is RNA splicing?

Removal of introns and joining of exons  

What are introns?

 Non-coding regions removed from RNA  

What are exons?

Coding regions kept in RNA  

What is the role of tRNA?

Brings amino acids to the ribosome  

What is an anticodon?

 A tRNA sequence complementary to an mRNA codon  

What is a ribosome made of?

rRNA and proteins  

What are the 3 ribosome sites?

A site, P site, E site  

What happens at the A site?

Incoming tRNA brings next amino acid  

What happens at the P site? 

Holds growing polypeptide chain  

What happens at the E site?

Empty tRNA exits  

What is the start codon?

AUG (codes for methionine)  

What are stop codons? 

UAA, UAG, UGA  

What happens in translation initiation?

Ribosome assembles at start codon with first tRNA  

What happens in translation elongation?

Amino acids are added and peptide bonds form  

What happens in translation termination?

Stop codon reached → protein released  

What are polyribosomes?

Multiple ribosomes translating one mRNA at once  

What does “coupled transcription and translation” mean?

 Both happen at the same time in prokaryotes  

What do free ribosomes produce? 

Proteins that function in the cytoplasm  

What do rough ER ribosomes produce?

Secreted or membrane proteins  

What is a mutation?

A change in DNA sequence  

How do mutations affect phenotype?

They can change protein structure/function  

What is a point (missense) mutation?

One base is substituted for another  

What is a nonsense mutation?

Mutation creates a stop codon  

What is a frameshift mutation

Insertion/deletion shifts reading frame  

Why can frameshift mutations be severe?

They change all downstream amino acids  

Why are mutations important evolutionarily?

They create genetic variation