Grade 12 biology - Hereditary Molecules of Life

histone

a special protein molecule that is the core around which the DNA strand wraps

Plasmid

a small circular section of DNA found in the cytosol of bacteria; replicates independently of the chromosomal DNA

Genome

the complete set of an organisms hereditary information

Transformation

A change in a genotype or phenotype caused by the direct uptake of genetic material by a cell

Bacteriophage

a virus that infects bacteria

purine

a class of nitrogenous bases with a double-ring structure; adenine and guanine are purines

Pyrimidine

a class of nitrogenous bases with a single-ring structure; thymine and cytosine are prymidines

Complementary base pairing

The chemical tendency of adenine to form hydrogen bonds with thymine, and cytosine to form hydrogen bonds with guanine

Semiconservative Replication

a mechanism of DNA replication in which each of the two strands of parent DNA is incorporated into a new double-stranded DNA molecule

Replication origin

A specific sequence of DNA that acts as a starting point for replication

Helicase

a replication enzyme that separates and unwinds the DNA strands

Replication fork

the point of separation of the two parent DNA strands during replication

Topoisomerases

a class of enzymes that relieve tension caused by the unwinding of parent DNA; they cleave one or two of the DNA strands, allow the strand(s) to untwist, and then rejoin the strand(s)

single-strand binding protein (SSB)

a replication enzyme that prevents parent DNA strands from annealing to each other once they have been separated by helicase

replication bubble

the separating of DNA in both directions during replication

nucleoside triposphate

A building block and energy source for replicating DNA

RNA primase

a replication enzyme that produces RNA primers

RNA primer

a replication molecule that acts as a starting point for replication

DNA polymerase III

a prokaryotic replication enzyme that builds new DNA strands from nucleotides

Leading strand

the DNA strand that is copied in the direction toward the replication fork

Lagging strand

the DNA strand that is copied in the direction away from the replication fork

Okazaki fragment

the piece of new DNA on the lagging strand

DNA polymerase I

a prokaryotic replication enzyme that fills in gaps in the lagging strand between Okazaki fragments; also proofreads the final strands

DNA ligase

an enzyme that catalyzes the formation of a phosphodiester bond between two DNA strands, as well as between Okazaki fragments

DNA polymerase II

a prokaryotic replication enzyme that repairs damage to DNA, including damage that occurs between replication events

Function of Helicase

Unwinds DNA helix

Function of Single-strand binding protein (SSB)

stops the two separated parent strands from annealing

Function of Topoisomerases

Cleave and then reattach one or two of the DNA strands to relieve tension created by the unwinding process

Functions of RNA primase

places RNA primers on template strands

Function of RNA primers

act as starting strands for DNA polymerase

Function of DNA polymerases

Several closely related enzymes that assemble nucleotides into new DNA strands; remove RNA primer nucleotides and replace them with DNA nucleotides; proofread and repair replication errors and other damage to DNA molecules

Function of DNA ligase

forms the phosphodiester bond that joins the ends of DNA that make up the Okazaki fragments

Nucleosome

a unit of DNA storage, consisting of eight histones with DNA strands wrapped around them; the DNA around each nucleosome is about 147 nucleotides in length

Solenoid

a group of six nucleosomes

supercoiling

the continuous twisting of prokaryotic DNA that reduces the volume of the DNA

telomere

a repeating sequence of DNA at the end of a chromosome that protects coding regions from being lost during replication

Telomeres have several functions:

-They help to prevent chromosome ends from fusing to other chromosomes

-They prevent DNA degradation from enzymes called nucleuses

-They assist DNA repair mechanisms in distinguishing DNA breaks from chromosomal ends

-They may play a role in determining the number of times that a cell can divide, and therefore may play a critical role in determining the lifespan of an organism

Cell senescence

The period in a cell’s lifespan when it loses the ability to divide and grow; often referred to as cell aging

Hayflick limit

The total number of times that a normal cell can divide

Telomerase

An enzyme that adds new telomere sequences to the ends of chromosomes