Genetics Chapter 12

Genetic Code features

written in linear form, each "word" within the mRNA consists of three ribonucleotide letters as a triplet code, the code is unambiguous, the code is degenerate, contains one start and 3 stop codons that initiate and terminate translation, the code is non

Frameshift mutations

result from the addition or deletion of one or more nucleotides within a gene and subsequently the mRNA transcribed by it. shifts the frame of reading during translation

RNA homopolymers

made with only one time of ribnucleotide

RNA heteropolymers

made with multiple types of ribonucleotides

Nirenberg & Leder

triplet binding assay

triplet binding assay

led to specific assignments of triplets. if it stuck to the filter then that is the triplet that the tRNA binded to. The amino acid to be tested was made radioactive and charged tRNA was produced, they were then put through a filter and the one that remai

anticodon

the triplet sequence that is complementary to a codon of mRNA

degenerate

one amino acid can be specified by more than one triplet

unambiguous

a single triplet specifies only one amino acid

wobble hypothesis

the first two letters are the sam and it is the third letter that is the one that changes. A pattern of degeneracy. Allows the anticodon of a single form of tRNA to pair with more than one triplet in mRNA

overlapping genes

since a single mRNA may have multiple initiation points for translation, they could create several different reading frames within the same mRNA, thus specifying more than one polypeptide

RNA polymerase

basically the same as DNA polymerase but it does not require a primer and has ribose not deoxyribose.

consensus sequences

these sequences are similar in different genes of the same organism or in one or more genes of related organisms

TATA Box

rich in adenine and thymine. A short nucleotide sequence upstream from the initiation site of eukaryotic genes to with RNA Polymerase 2 binds.

sigma factor

gives polymerase specificity on where transcription should be taking place. Promoter recognition. Added to core subunits=holoenzyme

hairpin secondary structure

the termination sequence that is transcribed into RNA forms a unique sequence of nucleotides and causes the newly formed transcript to fold back on itself creating this.

Termination factor

rho, a large hexameric protein that physically interacts with the growing RNA transcript

polycistronic mRNA

an mRNA that encodes more than one protein at a time. genes whose products are related are often clustered together on the chromosome, so it is efficient to be done this way because often the cell needs the proteins all at the same time, so it makes them

RNA polymerase 2

template binding step & promoter regions. Dependent upon both cis-acting elements surrounding the gene itself and a number of trans-acting transcription factors

core promoter

determines were RNP 2 binds to the DNA and where it begins copying the DNA to RNA

what influences the efficiency of transcription initiation by RNP 2?

proximal-promoter elements, enhancers, and silencers

Post-transcriptional modifications

5' cap and a poly-A tail

5' Cap

protects the 5' end of the molecule from nuclease attack. added even before synthesis of the initial transcript is complete and appears to be important to subsequent processing within the nucleus

Poly-A Tail

added at the 3' end after the initial transcript is cleaved. protects the mRNA. Critical if the mRNA is to be transported to the cytoplasm and translated

Splicing

the removal of the corresponding ribonucleotide sequences representing introns.

ribozyme

RNAs that are capable of catalytic activities

spliceosome

a huge molecular complex that mediates the splicing reactions.

snRNPs

small nuclear ribonucleoproteins. A protein that is in an essential set of small nuclear RNAs in a spliceosome. splicing commences once these are added.

Lariat

involves snRNPs, in intermediate structure is formed and the second reaction ensues, linking the cut 5' end and the intron to the A, contains the excised intron.
made up of introns folding back on themselves

alternative splicing

when introns present in pre-mRNAs derived from the same gene are spliced in more than one way

Making DNA 5'-3'

Reading DNA 3'-5'

Promoter

DNa sequence that transcriptional apparatus recognizes, indicates which strand of DNA will be transcribed, determines start site, usually not transcribed
-upstream of transcription

***

Terminator region is transcribed

rho-independent termination

contain inverted repeat sequences
hair pin structure formation is required. This structure causes RNA polymerase to pause, also may distabilize the complex

rho-dependent

requires protein
requires DNA sequence that causes a pause in transcription
stretch of DNA upstream of termination site that is devoid of structure

TFIID

First thing to bind to the TATA Box to position TNA pol II correctly.

RNA POL 1

requires a termination factor that binds to DNA downstream of termination site

RNA POL III

uses a termination sequence-requires no secondary structure

RNA pol II

termination is coupled to cleavage in the 3' UTR (untranslated region)