Information Systems in Biology

Information System

• Information is transmitted within and between individuals through various methods.
• DNA transmits information from one generation to the next using chemical substances.

Chemical and Electrical Signals

• Chemical signals (ligands/signaling molecules) are a common form of cellular communication.
• These signals are secreted by cells and travel through extracellular fluid to target cells.
• Examples include neurotransmitters and hormones.

Hormones

• Hormones are chemical signaling molecules produced by endocrine glands.
• They are secreted directly into the bloodstream and travel to distant tissues/organs.
• Only target cells with compatible receptors can respond.

Neurotransmitters

• Many animals use electrical signals for information transmission.
• The nervous system transmits information via neurotransmitters and electrical impulses.

Chromosomes

• Chromosomes are thread-like bodies present in the nucleoplasm of living cells, crucial for inheriting genetic information (genes) from one generation to the next.
• This genetic material is deoxyribonucleic acid (DNA).
• In prokaryotes (cells without a nucleus), the chromosome is a circular DNA structure.
• In eukaryotes (cells with a nucleus), chromosomes are more complex in structure.
• Eukaryotic genomes comprise multiple chromosomes.
• Diploid organisms (like humans) have two copies of each chromosome.
• Chromosome pairs share identical genes arranged in the same order, but often have different versions of the genes (alleles).
• Chromosomes vary in number across different organisms, but the number is specific for each organism.
• Chromosomes are essential for cell division, needing replication, division, and successful transmission to daughter cells.
• Chromosomes control organism growth and development.
• Chromosome structure and chromatin vary throughout the cell cycle.

Chromosome Structure

• Chromosomes are composed of chromatin, which contains DNA and associated proteins (histone proteins).
• Chromosomes are made up of many genes that code for various proteins in the cell.
• Chromosome structure can be best examined during cell division.

Main parts of Chromosomes

• Each chromosome has two symmetrical chromatids.
• Each chromatid contains a single DNA molecule.
• During anaphase of mitotic cell division, sister chromatids separate and migrate to opposite poles.

Centromere and Kinetochore

• Sister chromatids are connected by the centromere.
• Spindle fibers attach to the centromere during cell division.
• Centromere is the primary constriction point.
• Centromere divides a chromosome into two parts—p arm (shorter) and q arm (longer).
• The kinetochore is a protein complex assembled on the centromere before cell division.
• Each chromosome has two kinetochores on either side of the centromere during metaphase.
• The kinetochore acts as an interface between chromosomes and spindle microtubules.
• Kinetochores pull chromosomes apart during anaphase and ensure equal distribution of sister chromatids in daughter cells.

Secondary Constriction and Nucleolar Organisers

• Chromosomes have secondary constrictions besides the centromere (primary constriction).
• Secondary constrictions, called nucleolar organizers, contain genes that form nucleoli.

Telomere

• The terminal part of a chromosome is called the telomere.
• Telomeres are polar, preventing fusion of chromosomal segments.
• Telomeres shorten each time a cell divides, eventually leading to cell division cessation.

Satellite

• Sometimes, chromosomes have an elongated segment called the satellite located at the secondary constriction.
• Chromosomes with satellites are known as sat-chromosomes.

Chromatin

• Chromosomes are composed of chromatin, which is made up of DNA, RNA, and proteins.
• During the interphase, chromosomes are visible as thin chromatin fibers in the nucleoplasm.
• During cell division, chromatin fibers condense, making chromosomes visible with distinct features.
• Heterochromatin (darkly stained): condensed regions, contain tightly packed DNA, genetically inactive, and commonly found in constitutive heterochromatin.
• Euchromatin (light stained, diffused regions): contain loosely packed DNA, genetically active, and common in active genes.
• Chromatin material appears as thin filaments (chromonemata) during prophase.

Structural Organisation of Chromatin

• Chromatin is made of DNA and associated proteins.
• DNA is organized into nucleosomes, the basic units of chromatin.
• DNA coils around histone proteins to form nucleosomes.
• Five types of histone proteins exist in eukaryotic chromosomes.
• Histones are positively charged due to amino acids, enabling association with negatively charged DNA (due to phosphate groups).
• Histones play a role in gene regulation.
• Nucleosomes consist of 200 base pairs of coiled DNA around a core of eight histone molecules. Linked by linker DNA.
• Nucleosomes prevent DNA tangling.

Linker DNA

• Linker DNA and the fifth histone protein assemble adjacent nucleosomes into a compact chromatin fibre (30nm).
• These fibres coil to form extended chromatin (300nm), held together by non-histone proteins like actin, alpha/beta tubulin, and myosin (scaffolding proteins)

Nucleotide Binding and Bonding

• Nucleotides covalently bond through sugar-phosphate backbone (5' carbon of sugar to 3' carbon).
• Nucleotides form hydrogen bonds with opposing strand bases.
• Complementary base pairings: A-T (2 H-bonds) and G-C (3 H-bonds).
• Consistent base pairings maintain a uniform DNA diameter.

Base Pairs

• A-T pairings and G-C pairings maintain a consistent DNA diameter.

DNA Backbone

• DNA backbone is a polymer with an alternating sugar-phosphate sequence.
• Deoxyribose sugars in the backbone are connected through ester links to phosphate groups in a 3'-5' direction.

Features of the DNA Double Helix

• DNA consists of two intertwined strands running in opposite directions (antiparallel).
• The strands are arranged in a spiral (double helix).
• Nitrogenous bases are inside the helix, stacked atop each other.

A final structure for DNA

• DNA consists of two antiparallel strands.
• The right-hand chain is essentially upside-down.

RNA

• RNA consists of ribose, phosphate, and nitrogenous bases (purines, pyrimidines).

• RNA typically forms a single-stranded biopolymer.

• Nucleotides are linked by 5'-3' phosphodiester bonds between ribose sugars in the RNA backbone.

• RNA differs from DNA: uracil replaces thymine, and RNA contains a 2' hydroxyl group.

• Self-complementary RNA sequences can fold into complex structures.

How is RNA Made

• RNA polymerases synthesize RNA from DNA through transcription.
• RNA polymerase binds to the promoter region of DNA, unwinding it to expose the template strand.
• RNA polymerase uses the template DNA strand to synthesize a complementary RNA strand.
• The newly synthesized RNA strand is almost identical to the non-coding strand of the DNA, barring uracil replacing thymine.

Types of RNA

• mRNA serves as a template and carries genetic information out of the nucleus for protein synthesis.
• tRNA binds both mRNA & amino acids, bringing the correct amino acids to ribosomes during protein formation.
• rRNA constitutes 50% of a ribosome, a molecular assembly essential for protein synthesis.

Protein Synthesis

• The mechanism of RNA translation into protein consists of initiation, elongation, and termination steps.
• Initiation involves mRNA joining with tRNA and ribosomes.
• Elongation involves tRNA bringing amino acids according to codon sequences.
• During termination, ribosome encounters a stop codon, triggering polypeptide chain release and complex disassembly.