Gene Expression - Protein Synthesis

What is gene expression?

It is the process of converting genetic information into functional products like proteins.

Which molecules are associated with traits?

Proteins.

Which molecules must be expressed to form traits?

Genes must be expressed to produce proteins.

Do parents pass on traits directly to offspring?

No, they pass genes that must be expressed to result in traits.

Which molecule comprises genes?

DNA.

Where are genes found in eukaryotic cells?

In the nucleus, within chromosomes.

Difference between chromatin and chromosomes?

Chromatin is loosely packed DNA (active), chromosomes are tightly packed (during division).

Where are genes found in prokaryotic cells?

In the nucleoid region (circular DNA).

Which DNA types do you possess?

Nuclear DNA (nDNA), mitochondrial DNA (mtDNA).

Define a gene.

A sequence of DNA that codes for a functional product (usually a protein).

Which gene sequences code for protein?

Exons.

Which gene sequences do not code for protein?

Introns.

How much of the human genome codes for protein?

About 1.5%.

What attaches to a promoter to begin gene expression?

Transcription factors.

What are the 3 processes to express a gene in eukaryotes?

Transcription, RNA processing, Translation.

Where does transcription occur?

In the nucleus.

Where does RNA processing occur?

In the nucleus.

Where does translation occur?

In the cytoplasm at ribosomes.

Define template strand.

DNA strand used to make RNA (read 3'→5').

Define coding strand.

DNA strand that matches RNA (5'→3') except T → U.

Define ssRNA.

Single-stranded RNA.

Define polypeptide.

A chain of amino acids (protein).

What is the central dogma?

DNA → RNA → Protein.

Name the 4 types of ssRNA.

mRNA, tRNA, rRNA, miRNA.

Which RNAs are involved in translation?

mRNA, tRNA, rRNA.

Which RNAs are made via transcription?

All 4: mRNA, tRNA, rRNA, miRNA.

What happens during transcription?

DNA is copied into RNA.

Which enzyme performs transcription?

RNA polymerase.

Which strand is transcribed?

The template strand.

What happens during RNA processing?

Introns are removed, exons spliced, 5' cap and poly-A tail added.

What happens during translation?

mRNA is decoded into a polypeptide chain.

Which organelle carries out translation?

The ribosome.

Define codon.

Three-base sequence on mRNA that codes for an amino acid.

Define anticodon.

Three-base sequence on tRNA that matches a codon.

Are codons beyond start and stop translated?

No, only codons between start and stop codons are translated.

What does mRNA do in translation?

Carries genetic instructions from DNA.

What does tRNA do in translation?

Brings amino acids to the ribosome via anticodon-codon pairing.

What does rRNA do in translation?

Forms the core of ribosome and catalyzes peptide bond formation.

What do ATS enzymes do?

Attach correct amino acids to their corresponding tRNAs.

What are protein domains?

Functional parts of proteins encoded by exons.

Can a domain appear in more than one protein?

Yes.

What is exon shuffling?

Recombining exons to create new proteins.

What is alternative splicing?

Processing the same pre-mRNA in different ways to produce multiple mRNAs.

When does alternative splicing occur?

During RNA processing.

Why is alternative splicing significant?

It increases protein diversity from one gene.

Estimated size of transcriptome vs genome?

Transcriptome has over 100,000 transcripts; genome has ~21,000 genes.

What are miRNAs?

Small RNAs that regulate gene expression by binding to mRNA.

What happens when miRNAs bind reversibly?

Translation is temporarily blocked.

What happens when miRNAs bind irreversibly?

mRNA is degraded.

3 types of post-translational modifications?

Phosphorylation, Glycosylation, Ubiquitination.

Purpose of post-translational modifications?

Modify activity, stability, or location of proteins.

Where do post-translational modifications occur?

ER, Golgi, cytoplasm.

What happens if proteins are activated too soon?

They may interfere with normal cell function.

What is a maladaptive outcome of protein synthesis?

Misfolded proteins (MFPs) accumulate and cause damage.

What does a cell do with MFPs?

Uses chaperones, degrades them, or triggers apoptosis.

Link between MFPs and neurodegenerative diseases?

Accumulation of MFPs is involved in diseases like Alzheimer’s and Parkinson’s.

What is a prion?

A misfolded, infectious protein.

Examples of MFP/prion diseases?

Alzheimer's, Parkinson's, Huntington's, ALS; CJD, BSE (mad cow), Scrapie.

Which neuro diseases affect brain?

Alzheimer's, Parkinson's, Huntington's.

Which neuro disease affects spinal cord?

ALS (Amyotrophic Lateral Sclerosis).

What is protein affinity?

How strongly a protein binds to a target.

What determines protein affinity?

Shape and chemical interactions (charge, polarity).

Which SARS-CoV-2 protein binds to human receptor?

Spike protein binds to ACE2 receptor.

Why is this binding important for virus?

Allows entry into human cells.

What happens to affinity if protein changes?

Affinity can increase, decrease, or disappear.

Which SARS-CoV-2 protein binds human defense proteins?

Spike protein binds neutralizing antibodies.

When are antibodies made?

After infection or vaccination.

What do antibodies do?

Block viral entry and mark virus for destruction.

Define antigen.

Any foreign molecule that triggers immune response.

Define antigenic.

Capable of triggering an immune response.

Which peptide ligand binds opioid receptor?

Endorphins (natural), morphine (drug).

Difference between endogenous and exogenous opioids?

Endogenous = made in body; exogenous = from outside.

What does analgesic mean?

Pain-relieving.

Why are opioids addictive?

They activate reward systems and release dopamine.

Function of antibodies?

Recognize and neutralize pathogens.

Function of polymerases?

Synthesize DNA or RNA.

Function of reverse transcriptase?

Converts RNA to DNA (in retroviruses).

Function of proteases?

Break down proteins.

Function of cytokines?

Signal molecules for immune response.