Cell Biology Basics

Cell Basics

• A cell is the smallest, basic unit of life responsible for all life processes.
• Robert Hooke discovered cells in 1665 while observing bottle cork under a microscope; the structures resembled prison cells.
• Cells are the structural, functional, and biological units of living organisms.

Cell Biology Defined

• Cell biology is the study of cell structure, function, and behavior.
• It is also known as cellular biology or cytology

Universal Features of Cells

• Genetic information is stored in the same linear chemical code (DNA).
• Cells replicate genetic information by templated polymerization
• Portions of genetic information are transcribed into the same intermediary form (RNA).
• Proteins are used as catalysts.
• RNA is translated into protein in the same way.
• Life requires free energy
• All cells all function as biochemical factories utilizing the same basic molecular building blocks.
• All cells are enclosed in a plasma membrane that regulates the passage of nutrients and waste.
• A living cell can exist with less than 500 genes.

DNA as Hereditary Information Storage

• All cells store hereditary information in double-stranded DNA molecules.
• DNA consists of long, unbranched, paired polymer chains.
• DNA is formed from four types of monomers.
• A nucleotide consists of a sugar (deoxyribose) with a phosphate group and a base.
• The base can be adenine (A), guanine (G), cytosine (C), or thymine (T).
• A repetitive sugar-phosphate backbone is created from each sugar being linked to the next via a phosphate group. The backbone has a series of bases protruding from it.

DNA Replication via Templated Polymerization

• DNA is synthesized on a template formed by a preexisting DNA strand inside living cells.
• Bases on the existing strand bind to bases of the new strand.
• Complementary base pairing: A binds to T, and C binds to G.
• Base-pairing holds fresh monomers in place.
• The selection of the next monomer to be added to the growing strand is controlled by the base pairing properties of the bases.
• A double-stranded structure is created through complementary sequences of As, Cs, Ts, and Gs.
• The two strands twist to form a double helix.

RNA as an Intermediary

• DNA must express its information to guide the synthesis of other molecules; this is the information bearing function.
• This function is in all living organisms and leads to the production of RNAs and proteins.
• Transcription is the process begins with templated polymerization.
• During transcription, segments of DNA are used as templates for RNA synthesis.
• Translation is the process in that RNA molecules direct the synthesis of proteins.
• Proteins represent a different chemical class of polymers.

Proteins as Catalysts

• Protein molecules are long, unbranched polymer chains of monomeric building blocks.
• The monomers of protein, amino acids, are different from DNA/RNA ones.
• There are 20 types of amino acids, rather than 4 in DNA and RNA.
• Polypeptides (protein molecules) fold into a precise three-dimensional form with reactive sites.
• The folding process is a result of joining amino acids in a particular sequence.
• Amino acid polymers bind with specificity to other molecules.
• Polymers act as enzymes to catalyze reactions.
• Proteins maintain structures, generate movements, and sense signals.
• Each protein performs a function based on a genetically specified sequence of amino acids.
• The cell's genetic information into action is carried out by proteins

Life as an Autocatalytic Process

• Polynucleotides determine the amino acid sequences of proteins.
• Proteins catalyze many chemical reactions, including the synthesis of new DNA molecules.
• Genetic information in DNA is used to make both RNA and proteins.
• This feedback loop is the basis of self reproducing behavior in living organisms

RNA Translation into Protein

• The sequence of messenger RNA is read in groups of three nucleotides (codons).
• Each codon specifies a single amino acid in a corresponding protein.
• There are 64 possible codons, but only 20 amino acids.
• Several codons correspond to the same amino acid.
• Transfer RNAs (tRNAs) is the code read out by a class of small RNA molecules..
• Each tRNA attaches to a specific amino acid at one end
• Each tRNA displays a three-nucleotide sequence (anticodon) at the other end.
• The anticodon enables it to recognize a codon in mRNA.
• It recognizes through base-pairing.
• Segments of DNA are transcribed into separate mRNA molecules.
• Each segment codes for a different protein.
• Each DNA segment, coding for a protein, represents one gene.
• RNA molecules transcribed from the same DNA segment can be processed to produce alternative protein versions.
• A gene is defined as the segment of DNA sequence encoding a single protein or set of alternative protein variants (or RNA molecule).

Energy and Cells

• A living cell is a non-equilibrium dynamic chemical system.
• Cells must take in free energy and raw materials from the environment. This is required for cells to grow, and replicate.
• Necessary synthetic reactions occur with the uptake of raw materials and free energy.
• A cell will decay and die when the consumption of free energy stops.
• Free energy is required to faithfully replicate information and make complex molecules.

Cellular Biochemical Factories

• All cells make DNA, RNA, and protein.
• These macromolecules are composed of the same set of subunits.
• All cells contain and manipulate a similar collection of small molecules.
• This includes sugars, nucleotides, and amino acids.
• All cells need substances that are universally required.
• ATP (adenosine triphosphate) required for synthesis of DNA and RNA
• All cells make and use ATP for free energy and phosphate to drive reactions.

Plasma Membrane Universality

• All cells are enclosed by a plasma membrane.
• It serves as a selective barrier.
• This barrier allows the gathering of nutrients in the environment.
• This allows for products to get synthesized for own use
• Excretion of waste products also possible.
• The molecules forming the membrane are amphiphilic.
• Amphiphilic meaning composed of a hydrophobic (water-insoluble) part and a hydrophilic (water-soluble) part.

Minimal Gene Existence

• Mycoplasma genitalium, a bacterium, has one of the smallest known genomes
• This organism lives as a parasite in mammals.
• This bacterium makes large molecules (DNA, RNAs, proteins) and require the basic process of heredity
• Its environment that provides necessary small molecules.
• It has about 480 genes in its genome of 580,070 nucleotide pairs, representing 145,018 bytes of information.
• The rough size of a chapter of a book.
• A viable cell in today's environments requires at least 200–300 genes.
• Only about 60 genes are within the core set shared by all living species.