Molecular and Cellular Biology Lecture 2

Study Notes

Cells are the fundamental units of all living systems.
Specialization leads to the formation of tissues, which consist of groups of cells for specific functions.
There are 14 major tissue types including bone, muscle, nerve, and fat.
Over 200 different cell types exist with a common genetic code.

Eukaryotic cells can be single or multicellular, possess a nucleus, and have membrane-bound organelles.
Prokaryotic cells are single-celled organisms lacking a nucleus and membrane-bound organelles; they typically contain a single, rolled-up DNA strand.

Life relies on three critical molecules: DNA, RNA, and proteins.
DNA stores cellular information, RNA transfers information and synthesizes proteins, while proteins perform vital cellular functions and form structural components.

Nucleic acids like DNA and RNA are polymeric chains composed of nucleotides, which include:
- A nitrogenous base
- A five-carbon sugar
- A phosphate group.

DNA carries genetic instructions and has a double helix structure, discovered by Watson and Crick.
It consists of two complementary antiparallel strands running 5' to 3' and 3' to 5'.
The structure comprises nitrogenous bases (A, C, G, T), deoxyribose sugar, and phosphate groups.
Adenine pairs with thymine via double hydrogen bonds, while guanine pairs with cytosine through triple hydrogen bonds.
DNA is more stable than RNA due to its deoxyribose sugar.

Initiation: Helicase unwinds DNA, creating a replication fork; primase synthesizes an RNA primer.
Elongation: DNA polymerase adds nucleotides complementary to the template strand; lagging strand forms in fragments (Okazaki fragments).
Termination: Exonuclease removes RNA primers, DNA polymerase fills gaps, and DNA ligase seals the strands.
DNA replication is semi-conservative, retaining one original strand in each new DNA molecule.

RNA functions in protein coding and acts as a carrier.
RNA is structured as a single helix and runs from 5' to 3', including components similar to DNA.
It contains nitrogenous bases (A, C, G, U) with adenine pairing with uracil, and guanine pairing with cytosine.
RNA is less stable than DNA because of its ribose sugar.

Messenger RNA (mRNA): carries the genetic message from the nucleus to the ribosome for protein synthesis.
Transfer RNA (tRNA): transfers specific amino acids to the ribosome to build proteins.
Ribosomal RNA (rRNA): combines with proteins to form ribosomes.
Non-coding RNA: does not translate into proteins; examples include tRNA and rRNA.
Catalytic RNA: catalyzes chemical reactions.
Double-Stranded RNA: has complementary strands like DNA and can influence gene expression.