MCB150 Lectures 11-20: Key Concepts and Processes

Outer membrane and inner membrane

The two membranes of the mitochondria; intermembrane space between them.

Porins

Porins allow molecules like ions to pass through; no regulation.

Pyruvate oxidation

Pyruvate is converted into acetyl-CoA, CO₂ is released, and NAD⁺ is reduced to NADH.

Citric Acid Cycle (CAC)

Produces 6 NADH, 2 FADH₂, 4 CO₂, and 2 ATP (per glucose).

Electron transport chain (ETC)

Creates a proton gradient across the inner membrane, used to generate ATP.

NADH and FADH₂ in ETC

NADH donates electrons to Complex I, and FADH₂ donates to Complex II, driving the ETC.

Final electron acceptor in ETC

Oxygen is the final electron acceptor, forming water (H₂O).

ATP generated from one glucose molecule

36 ATP (including glycolysis, CAC, and ETC).

ATP generated from glycolysis

2 ATP (net).

Fermentation

Regenerates NAD⁺ by converting pyruvate to lactic acid or ethanol.

Types of fermentation

Lactic acid fermentation and ethanol fermentation.

Central dogma of molecular biology

DNA → RNA → Protein.

Chargaff's rule

A = T (or U), and C = G; the amounts of A and T, C and G are equal.

Bonds holding base pairs in DNA

Hydrogen bonds (2 bonds between A-T and 3 bonds between C-G).

Meselson-Stahl experiment

Confirmed the semiconservative model of DNA replication.

Conservative vs. semiconservative replication

In conservative replication, the parental strands remain intact, while in semiconservative, each new DNA molecule has one parental and one daughter strand.

Role of helicase in DNA replication

It unwinds the DNA strands by breaking hydrogen bonds.

Leading vs. lagging strands

The leading strand is synthesized continuously, while the lagging strand is synthesized in Okazaki fragments.

DNA polymerase III

Responsible for synthesizing DNA after a primer is laid down in prokaryotes.

Role of DNA ligase

It seals nicks by forming phosphodiester bonds between Okazaki fragments.

Function of telomerase

Telomerase extends the ends of chromosomes (telomeres), preventing shortening during replication.

Nucleosomes

Consist of DNA wrapped around histone proteins; they help organize and compact DNA.

Euchromatin vs. heterochromatin

Euchromatin is loosely packed and transcriptionally active; heterochromatin is tightly packed and inactive.

Enzyme responsible for transcription

RNA polymerase.

Steps of transcription in prokaryotes

Promoter recognition, initiation, elongation, termination.

Coding vs. template strands in transcription

The template strand is used to synthesize RNA, while the coding strand has the same sequence as the RNA (except U replaces T).

Introns and exons

Introns are non-coding regions removed from pre-mRNA; exons are coding regions that are spliced together.

Role of the spliceosome

Removes introns and connects exons.

Purpose of the 5' cap and poly-A tail

Protect mRNA from degradation and help with translation initiation.

Codon

A three-nucleotide sequence on mRNA that codes for an amino acid.

Structure and function of tRNA

tRNA has an anticodon that pairs with the mRNA codon and an amino acid attachment site.

Aminoacyl-tRNA synthetases

Charge tRNAs by attaching the correct amino acid to the tRNA using ATP.

Three steps of elongation in translation

Binding of charged tRNA to the A site, peptide bond formation, translocation.

Stop codon

Signals the end of translation; the three stop codons are UGA, UAA, and UAG.

Role of release factors in translation termination

They mimic tRNA and help release the polypeptide from the ribosome.

Polysome (polyribosome)

A complex formed when multiple ribosomes translate the same mRNA simultaneously.

Co-transcriptional translation in prokaryotes

Transcription and translation occur simultaneously in the cytoplasm, as there is no nuclear membrane separating the processes.