Biology Unit 12

Griffith

First major experiment searching for generic material that involved transformation between two forms of S pneumoniae.

Avery

Identified the molecule that transformed the R strain of S pneumoniae into the S strand and concluded that when S cells were killed DNA was released.

Hershey and Chase

Used radioactive labeling to trace bacteriophage DNA and protein and concluded that bacteriophage DNA was injected into the cell and provided genetic information to produce new viruses.

Nucleotides

Subunits of nucleic acids that consist of 5-carbon sugars, the phosphate group, and nitrogenous bases

Chargaff

Analyzed the amount of A, G, T, and C in the DNA of various species.

Chargaff’s rule

C=G, T=A

Scientists who searched for the structure of DNA

Rosalind Franklin, Maurice Wilkins, Francis Crick, and James Watson

X-ray diffraction

Indicated DNA was a double helix formed by two strands of nucleotides twisted around each other

Watson and Crick

Using others data, they measured the width of the helix and the spacing of the bases and build a model

DNA structure

A double helix like rails of a ladder represented by the alternating deoxyribose and phosphate

DNA molecule orientation

top rail: 5’ to 3’, bottom rail: opposite direction 3’ to 5’

Prokaryote chromosome structure

DNA molecules are contained in the cytoplasm, and consist mainly of a ring of DNA and proteins

Eukaryote chromosome structure

DNA is organized into individual chromosomes

Nucleosome

DNA and histones which group together into chromatin fibers, which supercoil to form a chromosome

Semiconservative replication

parental strands of DNA sperate, serve as templates, and produce DNA molecules, that have one strand of parental DNA and one strand of new DNA

Processes of semiconservative replication

unwinding, pairing, and joining

Unwinding

DNA helicase unwinds the helix, breaking down the hydrogen bonds between bases, single-stranded binding proteins keep the DNA strands separate, and RNA primase adds a short segment of RNA primer

Base pairing

DNA polymerase adds appropriate nucleotides to the new DNA from the 3’ end while the leading strand is built continuously, the lagging strand is built discontinuously

Okazaki fragments

small segments of the lagging strand build discontinuously

Joining

DNA polymerase removes the RNA primer and fills in the place with DNA nucleotides and DNA ligase links the two segments

Eukaryotic DNA replication

DNA unwinds in multiple areas as DNA is replicated

Prokaryotic DNA replication

the circular DNA strand is opened at one origin of replication

RNA

a nucleic acid similar to DNA, but with the sugar ribose and uracil instead of thymine

Messenger RNA (mRNA)

long strands of RNA that are formed complementary to one strand of DNA; direct synthesis of a specific protein

Ribosomal RNA (rRNA)

Associates with proteins to form ribosomes in the cytoplasm

Transfer RNA (tRNA)

Smaller segments of RNA that transport amino acids to the ribosome

Transcription

the process that involves the synthesis of mRNA from DNA

RNA polymerase

an enzyme that regulates RNA synthesis by binding to the specific section where an mRNA will be synthesized

Introns

DNA sequences not found in mRNA

Exons

DNA sequences that remain in the final mRNA

Codon

the three-base code in DNA or mRNA found in experiments performed in the 1960s

Translation

the process where the mRNA code is read and translated into a protein where tRNA molecules act as interpreters of the mRNA codon sequence

Ribosome

organelle that provides a site for protein synthesis that holds the mRNA in place for translation and grooves for tRNA sites for amino acid attachments

Beadle and Tatum experiment

one gene codes for one enzyme

Gene regulation

the ability of an organism to control which genes are transcribed in response to the environment

Operon

a section of DNA that contains the genes for the proteins needed for a specific metabolic pathway

Operators

on/off switch in operons

Promoter

in operons where RNA polymerase binds

trp operon

a responsible operon that controls tryptophan synthesis

lac operon

an inducible operon when lactose is present E coli can synthesize an enzyme to use as an energy source

Transcription factors

ensure that a gene is used at the right time and that proteins are made in the right amounts

Complex structure of eukaryotic DNA

regulates transcription

Hox genes

A group of genes that control cell differentiation that are transcribed at specific times in specific places on the genome and control what body part will develop at a given body location

RNA interference (RNAi)

can stop the mRNA from translating its message by single-stranded small interfering RNA and protein complexes binding to the mRNA

Mutation

a permanent change that occurs in a cell’s DNA

Point mutation

mutation involving chemical change to just one base pair

Missense substitutions

DNA codes for the wrong amino acids

Nonsense mutation

In a mutation when a codon for amino acid becomes a stop codon

Insertion/deletions

additions/loss of a nucleotide to the DNA sequence that causes “frameshifts”

Mutagens

certain chemicals and radiation that can damage DNA

Mutations in sex cells

mutations passed on to the organism’s offspring and will be present in every cell of the offspring causing an entire person’s cells to have the mutation