Transcription and Translation - Bio 102

tRNA

transfer – transfers the amino acid that connects to mRNA

mRNA

messenger – template to make amino acid code

rRNA

ribosomal - makes up ribosomes

transcription

synthesis of mRNA from a single gene

template strand

the strand that mRNA is made off of

coding strand

the strand that is the same as the RNA strand (with exception to the thymine/uracil)

RNA Polymerase

major enzyme in transcription

polymerase activity

puts the building blocks of mRNA together

helicase activity

• unwinds the double helix

• unzips the two DNA strands

3 types of RNA polymerase in eukaryotes

I, II, III

RNA polymerase I

transcribes most rRNA genes

RNA polymerase II

• the one we care about most

• transcribes all protein-coding genes

• miRNA genes

• genes for other noncoding RNAs

RNA polymerase III

• transcribes most tRNAs

• 5S rRNA gene

• other small RNAs

promoter region

helps direct transcription

two components of promoter region

• TATA box

• transcription factors

TATA box

always upstream of the gene

• define the direction of transcription and indicate where RNA polymerase should start reading the DNA

transcription factors

• These lead to transcription  

• They bind to promoter and tell polymerase where to start  

• Help determine which is the coding strand and which is the template strand – tells them which direction the RNA polymerase should go  

direction RNA polymerase reads DNA

3’ to 5’

direction RNA polymerase makes RNA

5’ to 3’

terminator sequence

blocks the RNA polymerase which causes it to fall off and release the DNA

how transcription is affected by drugs

• helicase activity is halted

• polymerase activity is halted

difference between prokaryotic and eukaryotic transcription

prokaryotes

• In cytosol  

• 1 type of RNA polymerase  

• Sigma factor (subunit of RNA polymerase) recognizes promoter region  

• Termination signal in DNA  

• Transcription and translation kinda happen at the same time, so splicing doesn’t happen  

• They just have coding regions, eukaryotes also have introns (noncoding regions) 

Eukaryotes

• In nucleus... TRANSLATION occurs in the cytosol   

• 3 types of RNA polymerase  

• Requires transcription factors  

• Termination signal in mRNA (AAUAA)

3 processes to get RNA ready for translation in eukaryotes

• capping

• splicing

• poly-A tail

splicing

removing introns, keeping exons

splicesome

takes two exon ends, puts them together, and takes out introns

capping

• put on the 5’ end (first part made)

• protects from degradation and determines how long the RNA will stay in your cells

poly-A tail

• on the 3’ side

• 150-250 A’s

• helps protect from degradation and determines how long the RNA will stay in your cells

alternative splicing

• can produce different proteins by splicing out different introns

• anything between the introns can be taken out, but the ends need to stay

exporting mRNA from the nucleus

mRNA is exported from the nucleus through pores and channels into the cytosol

• cap-binding protein takes it out of the nucleus (this is a reason why we need capping)

• poly-A binding protein hooks on to the tail

once the mRNA exits, initiation factors replace the other proteins

nuclear pore complexes

form channels in nuclear membrane and can regulate exit of mRNA

codon

3 mRNA letters used to create an amino acid

tRNA

contains anticodons that are complementary to the codons of the mRNA

start codon

AUG - methionine

• keeps the mRNA in the correct reading frame

wobble base pairing

allows multiple codons to code for the same amino acid

• allows for some mutations and mistakes

large subunit

holds the tRNA

small subunit

holds the mRNA

initiation

• MRNA binds to the small subunit, the start codon is read (5’ to 3’), and this triggers the tRNA to come next  

• The tRNA is gonna come first, and then the large subunit comes on after

  • Every amino acid enters at the A site, EXCEPT the initiator tRNA which enters at the P (peptide) site

elongation

Another tRNA is added and this pushes the first tRNA to the P site where a peptide bond combines the amino acids  

Termination  

• Stop codon is reached  

• Instead of a tRNA with an amino acid, a release factor comes in with no amino acid  

• Since there is nothing for the amino acid chain to bond with, it is released  

• Everything breaks apart and can get used again

A site

aminoacyl

• where the tRNA enters

P site

peptide site

• where a peptide bond combines the amino acids

E Site

exit

• where the tRNA exits the ribosomes

chargaff’s rules

A goes with T

C goes with G

purines

A G

pyrimidines

C and T

purpose of genetic information

serves as “instructions” for building and maintaining cells

what genetic information is made of

DNA

how genetic information is stored

genes

base that is not common to DNA and RNA

thymine is replaced with uracil in RNA

5’ end

5th carbon on a sugar that connects to the phosphate group at the end of the strand

3’ end

3rd carbon on the sugar

number of bonds between G-C

3 hydrogen bonds

number of bonds between T-A

2 hydrogen bonds

differences between DNA and RNA

DNA

• double stranded

• deoxyribose (less oxygen)

• contains T

RNA

• single stranded

• ribose (more oxygen)

• contains U

genes

segments of DNA that code for RNA which is then translated into a protein

amino acid structure

number of different side chains in amino acids

20

how peptide bonds are formed

The –OH of the carboxyl group of the first

amino acid and the H from the amino

group of the next one are removed as a

water molecule – a condensation

(dehydration) reaction

• bond between the C and the N

N terminus

beginning of amino acid

C terminus

end of the amino acid

primary protein structure

linear sequence of a chain of amino acids

• linked by peptide bonds

secondary protein structure

formed by hydrogen bonds between protein backbone

• alpha-helix

• beta-pleated sheet

tertiary structure

• overall 3-D structure

• involved interactions between side chains

interactions that contribute to tertiary structure

• hydrophobic interactions

• hydrogen bonds

• disulfide bridge

• ionic bond

quaternary structure

multiple subunits assembled into a larger complex

chaperone proteins

help ensure that proteins fold properly

• form isolation chambers to provide the idea environment for protein folding