Protein Synthesis, Repression, & Mutations

Transcription

DNA transcribed to make RNA 📝

Where does transcription occur in eukaryotes vs. prokaryotes?

• Eukaryotes=Nucleus

• Prokaryotes=Cytoplasm

What are the 3 steps of transcription?

• Initiation 🟢

• Elongation 🟡

• Termination 🔴

What is the “promoter” region called and its sequence?

TATA Box (TATAAA) 

What are the 4 steps of transcription initiation? 🟢 

• RNA Polymerase binds to TATA Box Promoter

• helps unwind DNA H+ bonds

• → transcription bubble formed 🫧

• RP reads DNA template in bubble

How is RNA synthesized during initiation?

• thru complementary base pairing of nucleotides

• use DNA template

  • (e.g., TATAAA → AUAUUU).

• What do upstream/downstream mean in transcription?

• which direction does RNA Polymerase move?

• Upstream = left of promoter;

• Downstream= right of promoter

  • down, it moves 5’→3’

What are the 4 steps of transcription elongation? 🟡

• RNA Polymerase moves downstream

• it adds nucleotides to the 3’ end

• → mRNA transcript elongated

• previous DNA rewinds back to double helix 🧬

What are the 3 steps of transcription termination 🔴

• RNA Polymerase reaches DNA terminator sequence

• RNA polymerase & mRNA released

• DNA fully re-winds to its helix 🧬

What happens specifically to mRNA in termination? 🔴

• mRNA is released ◝(ᵔᗜᵔ)◜

• so it travels nucleus → attaches to a ribosome

Translation

mRNA carries gene to be translated into amino acid chain to make protein💌

Where does translation occur?

ribosome in cytoplasm

3 functions occurring in ribosome in translation:

• reads mRNA sequence codons 💌

• pairs mRNA codons to tRNA codons

• links amino acids to build polypeptide chain 

What holds amino acid chains together? ⛓

Peptide bonds 

Define a codon and give an example 

• mRNA triplet bases that code for 1 amino acid

  • DNA’s TAC → mRNA’s AUG 

How many mRNA bases code for 1 amino acid 

3 bases = 1 codon = 1 amino acid.

• What is the start codon

• amino acid it codes for?

• AUG signals start of translation

• Methionine.

Function of stop codons & what are the 3

• signal end of translation:

  • UAA

  • UAG

  • UGA

How many total codons exist in the genetic code?

64 triplet codons.

Why is the genetic code described as “redundant”/“degenerate”?

bc multiple codons can code for same amino acid.

• How many ‘sense’ codons

• & what do they code for

• 61 sense codons

• amino acids

• How many ‘nonsense’ codons are there

• what do they code for

• 3 nonsense codons

• stop signals

how tRNA and mRNA work tchugetha in translation

• tRNA carries amino acids from cytoplasm→ ribosome 🚛

• mRNA directs message for these amino acids

tRNA

• how long

• shape

• ~80 nucleotides

• H+ bonds twist into 3D L-shape (🍀)

Ribosome A site function

Holds tRNA carrying next amino acid to be added to chain

Ribosome P Site function

Holds tRNA carrying growing polypeptide chain ⛓

Ribosome E site function

where tRNA exits ribosome 

What are constitutive genes?

housekeeping genes always on expressed at fixed rate 🏡💡

Two regulated genes only expressed when needed

inducible & repressible genes 

Catabolite Repression function

• What does it prevent? 

• prefers+metabolizes glucose🍰 for energy efficiency

• expression of other genes to not waste energy 

• What is an operon & where mostly found?

• how it functions

• A cluster of genes mostly in prokaryotes

• regulatory protein binds near promoter to switch gene on/off 🎛

2 Functions of regulatory promoter gene?

• turn promoter & operators on/off,

• → controlling gene expression 

Lac Operon🍼

• default state

• turns operon on/off if _

• using _ 

• OFF (lactose absent)

• tuns ON if lac present 

• using Lac Operon Inducer, Allolactose

5 steps of how LAC operon is induced

1. Allolactose binds to the ACTIVE repressor protein

2. repressor changes shape → INACTIVE

3. INACTIVE repressor can’t bind to !OPERATOR

4. RNA polymerase now free to bind to operator

5. Transcribes lacA, lacY, lacZ,

lacZ, lacY, lacA

enzymes that break down lactose

Tryptophan Operon 🦃

• default state

• turns operon on/off if _

• using _ 

• ON (tryp absent)

• turns OFF if tryp is in excess

• using a corepressor 

5 steps of how Tryp operon is repressed

1. Tryptophan binds to INACTIVE repressor protein,

2. changes its shape→ ACTIVE

3. ACTIVE repressor binds to !OPERATOR  

4. RNA Polymerase now blocked,

5. cant transcribe genes E-D-C-B-A anymore 

Function of genes E-D-C-B-A

synthesize/make tryptophan 

In Catabolite Repression, what 5 steps occur if:

• glucose is absent but lactose is present?

• cAMP levels rise ↑

• cAmp binds to CAP→ cAmp-CAP complex

• complex binds near !PROMOTER

• RNA polymerase binds so

• Lac operon turns on for lactose metabolism.

In Catabolite Repression, what 5 steps occur if:

• glucose is present?

• cAMP levels drop ↓

• prevents cAMP–CAP complex 

• complex cant bind near !PROMOTER!

• RNA polymerase cant bind

• → Lac operon stays off.

Change in genetic material (*neutral, beneficial or harmful*)

Mutation

• Agent that causes mutation

• 2 examples

• Mutagens🐢

  • chemicals

  • radiation 🧪☢

What are the two main types of mutations & what they change 

• Frameshift Mutation: inserts or deletes 1/+ nucleotide

• Point/Base Pair/Substitution Mutation: changes 1 base pair

What happens in frameshift mutation

• 1+ nucleotide inserted/deleted

• → shifts whole sequence after

What are the 3 types of point mutations & describe

• Silent – No change (ex: UUU → UUC, phe → phe)

• Missense – Changes to a diff amino acid (ex: UUU → UUA, phe → leu)

• Nonsense – changes to a stop codon (ex: UAC → UAG, phe → stop)

2-aminopurine:

• replaces _

• pairs w _

• Replaces adenine

• cytosine instead of thymine (ex: AT now AC)

5-bromouracil

• is a _

• mistaken for __ by __

• pairs with _

• anticancer drug

• thymine by enzymes

• cytosine instead of adenine (ex AT now AC)

ionizing radiation:

• 2 examples

• cause __

• X-rays & gamma rays

• ions to damage nucleotides & DNA’s sugar-phosphate backbone