Host-Vector System
Class 12 · Biotechnology
5 ideas in Class 12 Biotechnology, explained in plain words, with games and quizzes to practise.
Hosts That Carry Cloning
Part of: The Host-Vector Partnership
A host is the living cell that receives carrier DNA, copies it and passes it on. A good host accepts the carrier easily, supports its copying, grows fast and is simple to handle, which is why a gut bacterium is the workhorse of school-level cloning.
Why it matters. A wrong host wastes the whole experiment: the carrier may refuse to enter or fail to copy. Knowing host traits helps you predict which cell will multiply your gene fastest.
Key words
- host
- : The cell that takes in carrier DNA and copies it.
- E. coli
- : A fast-growing gut bacterium widely used for cloning.
- compatibility
- : How well a carrier and host work together for copying.
- transformation
- : The entry of outside DNA into a host cell.
- progeny
- : The daughter cells that inherit copied DNA.
Try it in two minutes
- Name the two partners: carrier DNA and the host cell that copies it.
- List three host traits: easy entry, steady copying, fast simple growth.
- Ask why a fast-dividing microbe beats a slow-growing one for bulk copies.
Try at home. Compare doubling speeds of two microbes you read about and pick the faster copier.
What Makes a Good Vector
Part of: The Host-Vector Partnership
A cloning vector is carrier DNA with four essentials: a start signal for copying, single cut spots for pasting the gene, a marker to spot carriers, and small size for easy handling. Each part solves one failure: no start means no copies, many cuts means a mess, no marker means lost carriers.
Why it matters. Checking these four before an experiment saves weeks. You can read any new carrier map and predict whether it will copy, accept one gene paste and reveal itself.
Key words
- vector
- : Carrier DNA built to deliver and copy a chosen gene.
- origin of replication
- : The start signal where copying of DNA begins.
- selectable marker
- : A carried trait that reveals which cells hold the carrier.
- restriction site
- : A defined spot where cutting enzymes open DNA.
- insert
- : The chosen gene pasted into the carrier.
Try it in two minutes
- Draw a circle and mark three flags: start signal, one cut spot, one marker.
- Cover the marker flag and ask how carriers would be found.
- Cover the start flag and ask how many copies would form.
Try at home. Sketch any carrier map you meet and label its start, cut spot and marker.
Plasmid Vectors
Part of: Cloning Vectors in Action
Plasmids are small rings of bacterial DNA that copy on their own, so engineers build carriers from them. One classic carrier holds two resistance markers, letting growers spot pasting when one resistance is lost. A later carrier holds a colour gene, so plain carriers form blue colonies and pasted ones stay white.
Why it matters. These two tricks answer the daily lab question: which colonies hold my gene. Reading resistance loss and colour saves sequencing every colony.
Key words
- plasmid
- : A small self-copying DNA ring in bacteria.
- antibiotic resistance
- : A trait letting cells grow despite a germ-stopping chemical.
- insertional inactivation
- : Breaking a marker gene by pasting inside it.
- blue-white screening
- : A colour test where white colonies hold the pasted gene.
- colony
- : A visible pile of cells grown from one founder cell.
Try it in two minutes
- Draw a ring with two resistance flags for the classic carrier.
- Show pasting into one flag and ask which resistance stays and which goes.
- Show the colour gene broken by pasting and ask which colonies stay white.
Try at home. Draw both marker tricks from memory and label what each colour or loss means.
Phage and Hybrid Vectors
Part of: Cloning Vectors in Action
Bacterial viruses also serve as carriers. One famous virus yields two carrier types: one for small swaps and one for larger swaps. A thin thread-like virus suits single-strand work, while mixed carriers join plasmid parts with virus ends to haul bigger loads and slip into cells through viral coats.
Why it matters. Different gene sizes need different carriers. Knowing which hauls small, medium or large loads stops the error of forcing a big gene into a small carrier.
Key words
- bacteriophage
- : A virus that infects bacteria and can carry DNA.
- insertion vector
- : A virus carrier that accepts small extra pieces.
- replacement vector
- : A virus carrier with a removable stretch for larger pieces.
- cosmid
- : A mixed carrier with plasmid copying plus viral packing ends.
- phasmid
- : A mixed carrier joining phage and plasmid segments.
Try it in two minutes
- Line up four carriers from smallest to largest load.
- Ask which fits a tiny fragment and which fits a long one.
- Ask what the mixed carriers borrow from each parent: copying from one, coats from the other.
Try at home. Rank five carriers you meet by cargo size from memory.
Eukaryotic and Expression Vectors
Part of: Cloning Vectors in Action
Some jobs need more than bacterial carriers. Yeast-based giant carriers act like mini-chromosomes with end caps, a centre piece and a start signal, hauling huge stretches. Protein-making carriers add strong switches and stop signals, and dual-host shuttles carry two start signals to copy in both bacteria and higher cells.
Why it matters. Picking the right specialist avoids dead ends: giant loads need giants, protein harvests need switches, and moving between hosts needs a shuttle.
Key words
- artificial chromosome
- : A carrier built to behave like a tiny chromosome.
- promoter
- : A switch sequence that starts gene reading.
- terminator
- : A stop sequence that ends gene reading.
- shuttle vector
- : A carrier that copies in two different hosts.
- heterologous expression
- : Making a protein from one species inside another.
Try it in two minutes
- Draw a mini-chromosome with caps, centre and start signal.
- Draw a protein carrier with a switch at the front and a stop at the end.
- Draw a shuttle with two engines and ask which host uses each.
Try at home. For three jobs, name the specialist carrier and one part it must hold.
What your child will practise
- Eukaryotic and Expression Vectors: Ocean Quick Fire (Quick Fire)
- Hosts That Carry Cloning: Jungle Puzzle (Clue Puzzle)
- Phage and Hybrid Vectors: Candy Quick Fire (Quick Fire)
- Plasmid Vectors: Desert Puzzle (Clue Puzzle)
- What Makes a Good Vector: Space Quick Fire (Quick Fire)
- Quiz: Eukaryotic and Expression Vectors (8 questions)
- Quiz: Hosts That Carry Cloning (8 questions)
- Quiz: Phage and Hybrid Vectors (8 questions)
- Quiz: Plasmid Vectors (8 questions)