Nucleotides: The building block of a nucleic acid, consisting of a five-carbon sugar covalently bonded to a nitrogenous base and one to three phosphate groups.

Sugar-phosphate backbone: Forms the structural framework of nucleic acids, consisting of sugar and phosphate groups.

Nitrogenous base: Includes purines (adenine and guanine) and pyrimidines (cytosine, thymine, and uracil in RNA).

Chargaff’s rule: (1) the base composition of DNA varies between species

• In any species the percentages of A and T bases are equal and the percentages of G and C bases are equal

Watson and Crick: were the first to determine the structure of DNA

• Based on crystallogrphic images, were able to deduce that DNA was helical

• Watson built a model in which the backbones were antiparallel (their subunits run in opposite directions)

• First to determine the double-helical structure of DNA.

• Based on crystallographic images, deduced DNA was helical.

• Watson built a model showing that the backbones were antiparallel (their subunits run in opposite directions).

Wilkins and Franklin: produced a picture of the DNA molecule using crystallography

• Used X-ray crystallography to produce a picture of the DNA molecule, aiding the structural discovery.

Antiparallel:their subunits run in opposite directions 

• Describes the orientation of DNA strands; their subunits run in opposite directions.

5’ and 3’: Refers to the orientation of carbon atoms in the sugar molecule in DNA and RNA strands.

Chromatin: a complex of DNA and protein, is found in the nucleus of eukaryotic cells

• Undergoes striking changes in the degree of packing during the course of the cell cycle

Histone: proteins that are responsible for the first level of DNA packing in chromatin

• can undergo chemical modifications that result in changes in chromatin organization

Heterochromatin: condensed chromatin is called ___

• Dense packing of the heterochromatin makes it largely inaccessible to the machinery responsible for transcribing genetic information

Euchromatin: the more dispersed, less compacted chromatin is called __

Gene expression: The process by which DNA directs the synthesis of proteins.

Transcription: is the synthesis of RNA using information in DNA

• The first stage of gene expression 

• Three stages:

  • Initiation

  • Elongation

  • Termination

• All three stages require protein “factors” that aid in the translation process 

•  Energy is provided by hydrolysis of GTP

Messenger RNA: produced in transcription to carry genetic information to ribosomes.

Translation: Genetic information flows from mRNA to protein through the process of ___

• ___ is the synthesis of a polypeptide, using information in the mRNA

• In bacteria, translation of mRNA can begin before transcription has finished 

• In eukaryotes, the nuclear envelope separates transcription from translation 

• Eukaryotic RNA transcripts are modified through RNA processing to yield the finished mRNA

Triplet code: a series of nonoverlapping, threenucleotide words

• The flow of information from gene to protein is based on a ___

• The words of a gene are transcribed into complementary nonoverlapping three-nucleotide words of mRNA 

• These words are then translated into a chain of amino acids, forming a polypeptide

Codon: During translation, the mRNA base triplets, called ___, are read in the 5 to 3 direction 

•  Each one specifies the amino acid (one of 20) to be placed at the corresponding position along a polypeptide • The term codon is also used for the DNA nucleotide triplets along the nontemplate strand • The nontemplate DNA strand is also called the coding strand

Template strand: During transcription, one of the two DNA strands, called the ___, provides a template for ordering the sequence of complementary nucleotides in an RNA transcript

• always the same strand for any given gene 

• However, elsewhere on the chromosome, the opposite strand may function as the template for a different gene

Reading frame: Codons must be read in the correct ____ (correct groupings) in order for the specified polypeptide to be produced

Promoter: The DNA sequence where RNA polymerase attaches is called the ___

• signal the transcriptional start point and usually extend several dozen nucleotide pairs upstream of the start point

Terminator:  in bacteria, the sequence signaling the end of transcription is called the ___

Transcription factor: mediate the binding of RNA polymerase and the initiation of transcription

TATA box: A promoter DNA sequence called a ____ is crucial in forming the initiation complex in eukaryotesTranscription elongation

RNA polymerase: An enzyme called ___ pries the DNA strands apart and joins together the complementary RNA nucleotides

• assemble polynucleotides only in the 5 to 3 direction ¢ ¢ 

• Unlike DNA polymerases, ___ can start a chain without a primer

RNA processing: Enzymes in the eukaryotic nucleus modify pre-mRNA before the genetic messages are dispatched to the cytoplasm

•  During ___, both ends of the primary transcript are altered 

• Also, usually some interior parts of the molecule are cut out and the other parts spliced together

5’ cap: a modified form of a guanine nucleotide added to the 5' end of a newly synthesized pre-mRNA molecule in eukaryotic cells during RNA processing.  

Poly-A tail: a stretch of adenine nucleotides (A) added to the 3' end of a pre-mRNA molecule during RNA processing in eukaryotic cells.

RNA splicing: in ___ large portions of the RNA molecule are removed and the remaining portions reconnected

Exon: The other regions are called ___ and are usually translated into amino acid sequences

Intron: The noncoding regions are called intervening sequences

Transfer RNA: A cell translates an mRNA message into protein with the help of ___

• transfer amino acids to the growing polypeptide in a ribosome

• Each tRNA enables the translation of a particular mRNA codon into a certain amino acid • The tRNA contains an amino acid at one end and at the other end has a nucleotide triplet that can base-pair with the complementary codon on mRNA

• A ___ molecule consists of a single RNA strand that is about 80 nucleotides long

Codon: Three-nucleotide sequences in mRNA that specify amino acids.

 Anticodon: In three dimensions, tRNA is roughly L-shaped, where one end of the L contains the ___ that base-pairs with an mRNA codon

Aminoacyl-tRNA synthetases: Accurate translation requires two steps – First, a correct match between a tRNA and an amino acid, done by the ____

Wobble: Flexible pairing at the third base of a codon is called ___ and allows some tRNA’s to bind to more than one codon 

Ribosomes: are the sites of translation

rRNA: The large and small ribosomal are made of proteins and ___

A-site: A ribosome has a binding site for mRNA and three binding sites for tRNA – 1. The __ holds the tRNA that carries the next amino acid to be added to the chain

P-site: The ___ holds the tRNA that carries the growing polypeptide chain

E-site: The ___ is the exit site, where discharged tRNA’s leave the ribosome

Polypeptide: chains are modified after translation or targeted to specific sites in the cell

Ribosome initiation

• During synthesis, a ___ spontaneously coils and folds into its three-dimensional shape

 Polypeptide elongation

Polypeptide termination: occurs when a stop codon in the mRNA reaches the A site of the ribosome

• The A site accepts a protein called a release factor

Protein folding (primary to tertiary structure)

 Mutations: are changes in the genetic material of a cell

Point mutations: are chemical changes in just one nucleotide pair of a gene 

• The change of a single nucleotide in a DNA template strand can lead to the production of an abnormal protein

• If a ___  occurs in a gamete, it may be transmitted to offspring

Nucleotide-pair substitution: replaces one nucleotide and its partner with another pair of nucleotides

Silent mutation: have no effect on the amino acid produced by a codon because of redundancy in the genetic code

Nonsense mutation: change an amino acid codon into a stop codon, nearly always leading to a nonfunctional protein

Missense mutation: change one amino acid to another

Insertion: additions of nucleotide pairs in a gene 

Deletion: losses of nucleotide pairs in a gene

Frameshift mutation: Insertion or deletion of nucleotides may alter the reading frame of the genetic message, producing a ____ 

Mutagen: are physical or chemical agents that can cause mutations