BBL BIO BOI

What is the minimum requirement for a phage to sucessfully replicate?

It’s genetic material must enter the host cell (DNA)

If a phage attaches, but no new viruses form, what step likely failed?

DNA injection

Why does the host cell burst in the lytic cycle?

It becomes filled with newly assembled phages → pressure → lysis

Why must A=T and C=G in DNA?

Complementary base pairing rules (h-bond specificity)

Why can species have different base ratios if A=T and C=G?

The sequence of the bases differs, but pairing rules stay constant

DNA structure why?

Antiparallel structure is important for replication → allows proper alignment for complementary base pairing + enzyme function.

What would happen if base pairing rules were violated?

Mutations -: incorrect DNA replication → faulty protiens

What does the template strand mean in replication?

The original strand used to build a complemntary strand

What type of replication is used and why?

Semiconservative : each new DNA molecule contains one old strand + one new strand

Why do Eukaryotes have multiple orgins of replication?

Their DNA is much longer → replication must occur simaltenously in many locations

How does DNA structue support its function as gentic material

Stable (h-bonds) yet seperable → allows storage + replicaiton

Hershey-Chase experiment concluded

Directly idenitifed DNA was entering cells and controlling functions (proteins never entered)

Enchancers vs. Silencers

Enhancers: DNA sequences that increase gene expression by binding activators 

Silencers: DNA sequences that decrease gene expression by binding repressors 

What affects RNA stability? 

3' and 5' untranslated regions (UTR's) 

What is X-inactivation (Lynonization) and when does it occur? 

Females randomly inactivate one X chromosome in each cell in early development 

All but 1 -> (Inactive X chromsome = Barr body) 

What is the differnce between heterochromatin vs euchromatin

Heterochromatin is tightly packed and transcriptonally silent 

Euchromatin is loosely packed and actively transcribed 

What makes enchancers and silencers unique comapred to other promoter elements? 

They can act from great distances and work in either orientation 

What is the role of TFIID/TBP in eukaryotic transcription? 

Binds the TATA box and recruits other trancription factors in a cascade 

What are housekeeping genes? 

Genes expressed in all cells for basic metabolic functions

All cells in your body have identical DNA, yet a liver cell and a neuron look completely different. What explains this

Different cells express differnt genes (gene regulation decides which ones are expressed) 

Flow of gene expression DNA -> mRNA -> protein -> active protein 

Level	Controls	Key Idea
Transcriptional	DNA → mRNA	ON/OFF gene
Post-transcriptional	mRNA processing	modify mRNA
Translational	mRNA → protein	make protein or not
RNA interference	mRNA	block specific mRNA
Post-translational	protein	modify protein

1. Transcription factors, enchncers, silencers

2. Alternative splicing, mRNA stability

3. Ribsosme binding, blocking translation

4. Blocks mRNA using small RNA's (siRNA/miRNA) 

5. Phosphoryltaion (ON/OFF), Ubiquitin -> degradation   

The earlier you regulate -> more energy efficient 

The later you regulate -> faster response 

Which form of regulation is the most energy efficent? 

Transcriptional becuase you don't waste energy making proteins you don't need 

Which form of regulation is the fastest? 

Post-transcriptional becuase proteins already exist, just haveto modify them

Kinesases function to: 

Add phosphates 

What is the role of the Dicer? 

Processes small interfering RNA's 

• cuts RNA into sIRNA pieces

RNA interference works by: 

Blocking translation using complentary RNA

The TATA box is:

A promoter sequence (DNA) -> TFIID binds to it 

Ubiquinitiation leads to: 

Protein degradation

What is an example of post-translational regulation? 

Phosphorylation: Phosphate group is added to protein after it has been translated (can activate/deactivate the protein) 

mRNA levels in a cell are determined by: 

Balance of transcription and degradation 

Alternative splicing results in:

Multiple proteins from one gene 

(exons must remain in same order) 

• Different combindations of exons -> produce different proteins

What direction does DNA polymerase synthesize new DNA?

5’→3’ ONLY. can only add nucleotides to 3’ OH group (reads 3’→ 5”)

What enzyme unwinds the DNA double helix

Helicase

Why can’t DNA polymerase start replication on it’s own?

Needs a free 3’ OH group → Primase (creates RNA primer)

What is the function of DNA polymerase lll vs. I

DNA polmerase III: Adds nucleotides to build the new DNA strand

DNA polymerase I : replaces RNA primers with DNA

Which strand in DNA replication is syntheized continuoisly?

leading strand

Why are multiple RNA primers needed on the lagging strand?

Each Okazaki fragment needs its own starting point

A drug inhibits DNA ligase. What accumulates?

Unjoined Okazaki fragments

If DNA polymerase can’t proofread, what happens?

Increased mutation rate

What is Epistasis?

One gene affcets or hides the expression of another gene

A toxin blocks RNA polymerase activity, what will imediately follow?

mRNA production stops…

RNA polymerase: catalyzes transcription (synthesis of mRNA from DNA strand)

What is codon Degeneracy?

Multiple codons can code for the same amino acid

• typically 3rd position (wobble position) → doesn’t affect (silent mutation)

A unique property of RNA

RNA polymerase synthesizes RNA without a primer

What is the consequence if a frameshift mutation occurs early in the gene?

Entire downstream protein sequence changes

What type of bond joins amino acids into proteins

peptide bonds

Why must each tRNA carry a specific amino acid?

Codons deetermine amino acid sequence

If a drug prevents mRNA from leaving the nucleus what is the most direct effect?

Proteins cannot be synthesized