Cell and Molecular Biology Notes

Gene Expression and Regulation

  • All cells in an individual have the same genes, but they are read differently, except for a few specialized cells.
  • Different species have different versions of genes.
  • Genetic information provides instructions for function and behavior.
  • Regulation of gene expression is a molecular event that is itself regulated.

Cell Theory

  • A theory is a hypothesis that has been tested multiple ways and has yet to be disproven.
  • The quantity of evidence supports a theory.
  • Scientists do not "prove" something; they provide evidence or fail to disprove a hypothesis.
  • The cell theory states that all cells come from preexisting cells through cell division (mitosis or binary fission).
  • All living cells have the same basic fundamental chemistry and building blocks.
  • All life uses DNA as its genetic material.
  • Every living thing transcribes and translates genetic information into RNA and then into proteins using the same amino acids.

Last Universal Common Ancestor (LUCA)

  • LUCA is considered the first DNA-based individual surrounded by a membrane that could self-replicate.
  • The chemistry (DNA genetic material) is decoded into RNA and then translated into proteins using the same mechanisms.
  • This describes the fundamental flow of genetic information: DNA to RNA to protein.
  • Reverse transcription allows RNA to go back to DNA.
  • This is the central dogma of molecular biology.

Functional Molecules

  • mRNA is translated into protein.
  • Various RNA molecules (tRNA, rRNA, miRNAs, siRNAs, long non-coding RNA) regulate gene expression.
  • The function of the cell comes from the function of proteins and RNA molecules.

iClicker

  • iClicker will be used for participation and attendance.
  • Set up iClicker on a computer using a browser, not the app.
  • Enable precise location settings on the device used in class.
  • iClicker questions will be multiple-choice, and you can discuss them with others.

Genetic Information Flow

  • The proper flow of genetic information is DNA to RNA (transcription) to protein (translation).
  • RNA to DNA occurs via reverse transcription.

Characteristics of Life

  • Life must be able to self-replicate and produce additional cells.
  • Genetic information must be duplicated and passed on to offspring.
  • LUCA is the last universal common ancestor of cellular DNA-based life.
  • Prior to DNA, there was likely an RNA world.
  • Living cells are self-replicating collections of biochemical catalysts.

Catalytic Activity

  • Both proteins and RNA molecules have catalytic activities.
  • DNA and RNA contain information decoded into proteins, which have most of the catalytic activity.
  • Cells are self-replicating bags of biochemical catalysts.

RNA World

  • Life is currently composed of cells that are DNA-based.
  • The first cell was a simple DNA-based entity surrounded by a lipid bilayer (oil drop).
  • RNA likely predated DNA evolutionarily.
  • RNA can store information, self-replicate, and has catalytic activity.
  • DNA is a more stable, double-stranded molecule.
  • RNA maintains a major role in decoding information into functional products.

Ribozymes and Enzymes

  • Self-splicing RNA molecules can catalyze the splicing of introns.
  • A ribozyme is an RNA molecule that catalyzes a reaction.
  • An enzyme is a protein that catalyzes a chemical reaction.

Viruses

  • Viruses are nonliving parasitic entities that require a living host to duplicate.
  • Viruses do not grow or utilize energy resources on their own.
  • Viruses cannot translate their own information into protein without a host cell.
  • Some viruses have RNA-dependent RNA polymerase, but it is made by the host cell.

Ribonucleoproteins

  • If catalytic activity is carried out by a combination of protein and RNA, it is called a ribonucleoprotein.
  • Ribosomes are ribonucleoproteins.

Evolution of Genetic Material

  • RNA likely predated DNA as the original genetic information.
  • Proteins evolved through the process of translation.
  • DNA became the primary genetic information carrier due to its stability.
  • The order of evolutionary events: self-replicating RNA, translation, DNA replication and transcription.

Reverse Transcription

  • Changing from RNA to DNA requires reverse transcription.
  • Reverse transcriptase would be essential for this conversion.

Domains of Life

  • The three domains of life: Bacteria, Archaea, and Eukarya.
  • Archaea were previously grouped with bacteria but are more closely related to Eukarya.
  • Eukaryotes include animals, plants, protists, and fungi, possessing a nucleus and membrane-bound organelles.
  • Archaea are prokaryotes but are evolutionarily closer to eukaryotes.
  • Bacteria are constantly evolving new subspecies, often due to antibiotic resistance.

Prokaryotes

  • Prokaryotes lack a nucleus and are simpler organisms.
  • They typically have a single, circular chromosome.
  • Possession of a cell wall is common for bacteria, and they may produce a capsule.
  • Some prokaryotes can form colonies with specialized cells, bridging the gap between single-celled and multicellular organisms.
  • Even photosynthetic bacteria can have colonies with specialized cells (nitrogen fixation, desiccation resistance, photosynthesis).

iClicker Question Review

  • Endoplasmic reticulum is a membrane-bound organelle not found in prokaryotes.

Archaea

  • Archaea are a unique domain with unique biochemistry, enzymes, and cell walls.
  • Many archaea are involved in symbiotic relationships with bacteria and other archaea.
  • Ectosymbionts live externally associated with another living thing.

Eukaryotic Cells

  • Eukaryotic cells are defined by the presence of a nucleus.
  • Genetic information is found in the nucleus, mitochondria, and chloroplasts.
  • The nucleus contains the nuclear genome of 46 linear human chromosomes.
  • Mitochondrial and chloroplast genetic information is inherited maternally.