MOL-BIO LEC COMBINED PRELIMS

Nucleotides

Nucleic acids are polymers composed of monomers called

Sugar
Phosphates
Nitrogenous Bases

Nucleotides composed of three key components

Phosphate group

Serves as a source of ATP energy in cellular reactions.

Nitrogenous Bases

Participate in hydrogen bonding to form complementary base pairs.

Thymine (T), Cytosine (C), Uracil (U)

Single-ring (Pyrimidines)

Adenine (A), Guanine (G)

Double-ring (Purines)

Sugar-Phosphate Backbone

Provides structural support for nucleic acids.

Adenine (A) pairs with Thymine (T)
Cytosine (C) pairs with Guanine (G)

DNA base pairs:

Adenine (A) pairs with Uracil (U)
Cytosine (C) pairs with Guanine (G)

RNA base pairs:

Histones

DNA is wrapped around by this protein which help in packaging DNA within the nucleus.

Glycosidic Bonds

Link sugars to nitrogenous bases

Ester Bonds

Connect the sugar and phosphate groups.

Hydrogen Bonds

Hold complementary base pairs together.

DNA

Consists of a double helix model with two sugar-phosphate backbones and nitrogenous base pairs.

Helicase

Unzips the DNA by breaking hydrogen bonds, creating the replication fork

DNA Polymerase

Synthesizes new DNA strands by adding nucleotides using the parent strand as a template.

RNA Primase

Synthesizes a short RNA primer that serves as a starting point for DNA polymerase

DNA Ligase

Joins Okazaki fragments on the lagging strand.

Topoisomerase

Relieves tension and prevents supercoiling during DNA unwinding.

Single-stranded binding proteins

helps keep the DNA strands apart.

5’ to 3’

DNA polymerase can only add nucleotides in what direction

5’ to 3’

The leading strand is synthesized continuously in what direction

Okazaki fragments.

The lagging strand is synthesized discontinuously with this short fragment

3’ to 5’

Template strand of leading strand

Exonuclease

Removes the RNA primers from the Okazaki fragments.

GENE EXPRESSION

The process by which genetic information is converted into functional molecules, either proteins or RNA. It is controlled at various stages, leading to protein synthesis.

Exons

Coding sequences

Introns

Noncoding DNA

Transcription

RNA synthesis from a DNA template.

Translation

Ribosomes decode mRNA to form proteins.

Post-Translational Processing

Protein modifications for functionality.

Transcription
Translation
Post Transitional Processing

Protein Synthesis stages

Polymerase I

Synthesizes rRNA precursors

Nucleolus

Location of Polymerase I

Polymerase II

Synthesizes hnRNA (precursor to mRNA) and most small nuclear RNAs (snRNAs)

Nucleoplasm

Location of Polymerase II

Polymerase III

Produces 5S rRNA, tRNAs, and small cellular/viral RNAs

Nucleoplasm

Polymerase III location

Transcription Factors

Proteins that bind near the start of transcription.

Enhancers

DNA sequences (50-150 bp) that increase promoter activity.

Pre-Initiation Complex

Formed by general transcription factors + RNA polymerase.

Promoters

 DNA sequences upstream of a gene that regulate transcription.

mRNA processing

Process that is essential for converting the primary transcript (pre-mRNA) into a mature mRNA molecule ready for translation.

Capping

Added to the 5' end of the newly transcribed mRNA in the nucleus

Splicing

Introns (noncoding sequences) are removed, and exons (coding sequences) are joined together.

Poly(A) Tail

The 3' end of the mRNA is cleaved, followed by the addition of 40-200 adenine residues, forming the ______

Alternative splicing

Allows a single gene to produce multiple proteins by varying exon combinations.

Genetic Code

Determines how nucleotide sequences in mRNA are translated into proteins.

Triplet Code

Three nucleotides (codon) specify one amino acid.

UAG, UGA, UAA

3 stop codons

Translation

the process by which ribosomes decode mRNA to synthesize proteins.

Ribosomes

Protein synthesis machinery

tRNA

transports amino acids

60s
40s

Eukaryotic Ribosomes is composed of two subunits

A (Aminoacyl) site

 Binds incoming aminoacyl-tRNA.

P (Peptidyl) site

Holds the growing polypeptide chain.

E (Exit) site

 Binds free tRNA before it exits the ribosome.

RFs

Release factors in prokaryortes

eRFs

Release factors in eukaryotes

Plasma Membrane

A selectively permeable lipid bilayer with phospholipids, glycoproteins, and carrier proteins that regulate molecular movement.

Phospholipids

Membrane components with hydrophilic heads and hydrophobic tails, forming a bilayer that interacts with water.

Active Transport

ATP-dependent movement of molecules from low to high concentration.

Passive Transport

Energy-free movement of molecules from high to low concentration

Cytoplasm

Semi-fluid substance containing organelles, cytosol, filaments, and storage materials.

Nucleus

Control center housing DNA, directing growth, metabolism, and reproduction.

Mitochondria

Powerhouse of the cell, producing ATP through cellular respiration

Golgi Complex

Modifies, sorts, and packages proteins for transport via vesicles.

Ribosomes

Protein synthesis sites, found in the cytoplasm or on the rough ER

Smooth ER

Synthesizes phospholipids, digests lipids, and transports materials.

Rough ER

Protein-producing organelle covered in ribosomes, aiding extracellular protein and lysosomal enzyme synthesis.

Lysosomes

Contain digestive enzymes to break down cellular waste and materials.

Cell Wall

Rigid outer layer that protects and maintains cell shape.

Chloroplast

Site of photosynthesis, using light energy to produce ATP and sugars.

Central Vacuole

Large, fluid-filled organelle storing nutrients and waste.

Interphase

Cell growth and preparation for division, including DNA replication

G1 Phase

Growth phase before DNA replication.

S Phase

DNA replication, forming sister chromatids.

G2 Phase

Preparation for mitosis, including mitochondria division and spindle fiber synthesis

G0 Phase

Resting phase where non-dividing cells remain quiescent or senescent.

Mitosis

Cell division producing two identical nuclei.

Prophase

Chromosomes condense, centrioles move, and spindle fibers form.

Metaphase

Chromosomes align at the equator and attach to spindle fibers.

Anaphase

Chromatids separate and move to opposite poles.

Telophase

Two new nuclei form as chromosomes decondense.

Cytokinesis

Division of cytoplasm, forming two daughter cells.

Meiosis

Two-stage division producing four haploid gametes.

Prophase I

Homologous chromosomes pair and exchange genetic material (crossing over).

Metaphase I

Homologous pairs align at the equator.

Anaphase I

Homologues separate, but chromatids stay together.

Telophase I

Cytoplasm divides, forming two haploid cells.

Interkinesis

Brief rest period between Meiosis I and II.

Prophase II

Chromosomes condense, and spindle fibers reform.

Metaphase II

Chromosomes align at the equator.

Anaphase II

Chromatids separate and move to opposite poles.

Telophase II

Cytoplasm divides, resulting in four haploid cells.