Protein Synthesis

Gene expression

the process in which information in genes in DNA are used to form proteins

The Central Dogma

DNA is used to form RNA, which is used to produce proteins

A sequence of DNA that codes for a functional product (polypeptide chain or an RNA molecule) is called a ____

gene

Codon

codes for a specific amino acid

Each codon codes for only ___ amino acid

one

Each codon specifies the same amino acid in all _________

organisms

Triplet codons are how many bases long?

3

There are __ different codons and only 20 amino acids

64

Most amino acids are coded for by ____ than one codon

more

One start codon

where gene begins

Three stop codon

where gene ends

RNA carries genetic code from the nucleus to where?

the ribosomes

3 Types of RNA

• Messenger RNA (mRNA)

• Transfer RNA (tRNA)

• Ribosomal RNA (rRNA)

Messenger RNA 

takes the message from the nucleus to the ribosome

Transfer RNA

transfers the amino acids to the ribosomes

Ribosomal RNA

part of ribosome that joins amino acids together

Transcription (In nucleus)

DNA serves as a template for RNA formation

Translation (At the ribosomes)

mRNA directs the sequence of amino acids in a polypeptide chain 

• translating genetic code from nucleic acids to proteins

DNA and RNA are both..

nucleic acids

Transcription) The production of a primary transcript 

initial RNA from any gene

In prokaryotes, the primary transcript is used ________ in translation

directly

In eukaryotes, the primary transcript must be ________ before translation

modified

3 parts of a process

1) Initiation - start

2) Elongation - molecule gets longer

3) Termination.

In initiation, there are 2 strands of DNA, which are:

Template strand and Coding strand

Template strand

the strand of DNA that is transcribed

• used to produce RNA

Coding strand

the strand that is complementary to the template strand 

The sequence of the coding strand is identical to the primary transcript, except T is replaced with what?

U

Regions of DNA

Promotor, Terminator, and Transcription unit 

Promoter

sequence of DNA that signals the beginning of the gene

Terminator

sequence of DNA that signals the end of the gene 

Transcription unit

sequence of DNA that is transcribed

RNA polymerase, which does not require a primer, binds to DNA at the..

promotor

In bacteria, RNA polymerase can recognize..

the promotor by itself 

In eukaryotes, transcription factors regulate the..

binding of RNA polymerase to the promotor

Initiation in eukaryotes) Transcription factors recognize ____ box in promotor

TATA

Transcription factors and RNA polymerase form what?

the transcription initiation complex

The promote determines which strand of DNA is the _______ strand 

template

RNA polymerase separates the DNA into ___ strands and transcription begins

two

Elongation) RNA polymerase exposes about how many DNA bases at a time

20

Adds RNA nucleotides to which end of RNA transcript?

3’

Transcription proceeds in what direction?

the 5’ to 3’

As RNA polymerase moves along DNA, RNA transcript separates from DNA and DNA helix _______

reforms

Genes can be transcribed by several RNA polymerases simultaneously -

produces several primary transcripts

Termination0 In prokaryotes, transcription proceeds through what?

terminator 

In prokaryotes, signals RNA polymerase to detach from DNA and mRNA is released and is immediately available for what?

translation

In eukaryotes, transcription occurs through polyadenylation signal which is

AAUAAAA

At a point about 10-30 bases downstream from polyadenylation signal, proteins..

cut RNA from RNA polymerase and releases the primary transcript

RNA polymerase continues transcribing the DNA and enzymes quickly break down the..

additional RNA that is produced. 

When enzymes reach RNA polymerase, RNA polymerase ________ and transcription 

ends

Alteration of ends of RNA) 5’ cap

modified guanines added to 5’ end of primary transcript 

Poly-A tail

many adenines added to 3’ end of primary transcript after the polyadenylation signal

UTR’s are untranslated regions at both ends of a 

primary transcript 

Purpose of alteration of ends of RNA

• facilities transport of mRNA out of the nucleus

• protects mRNA from hydrolytic enzymes in the cytosol

• 5’ cap helps ribosome attach to mRNA during translation

mRNA splicing

introns are removed and exons are joined together

2 regions of RNA

intron and exon

Intron

noncoding regions

Exon

coding regions that exit the nucleus

Each exon may code for a different domain in a what?

protein 

Domain

a structural and/or functional region of a protein

• active site

Spliceosome

large complexes of proteins and small RNA molecules

Spliceosomes remove introns and join what together?

exons

RNA performs most of the..

catalytic functions

Ribozymes

some RNA molecules can act as enzymes

Examples

RNA in the spliceosome and rRNA

Properties of RNA that allow it to act as a catalyst

• Has a specific 3D shape - complementary base pairing between nucleotides within the molecule

• Has functional groups that can participate in chemical reactions

• Can hydrogen bond with specific types of nucleic acids

In alternative mRNA splicing, different segments of a primary transcript may be treated as..

introns and exons 

One gene can produce many different what?

polypeptide chains

The number of proteins an organism can make is _______ than the number of genes it has

greater

Alternative mRNA splicing is very common in..

humans

Translation

mRNA is used as a template for the amino acid sequence of a polypeptide chain

One type of tRNA for every..

amino acid

tRNA binds to an amino acid and carries it to the what?

ribosome

Anticodon

3 bases which are complementary to a codon of mRNA

Aminoacyl-tRNA synthetase

group of enzymes that bind amino acid to the correct tRNA

In bacteria, there are how many different types of aminoacyl-tRNA synthetase

45

Wobble in the third base position allows some..

flexibility

Correct amino acid and tRNA bind to the what of aminoacyl-tRNA synthetase?

active side

Enzymes use ATP to bond the amino acid to the what?

tRNA

The “charged” tRNA or aminoacyl tRNA is _________

released

Role of rRNA

• part of ribosome

• facilitates binding of mRNA with tRNA

• binds amino acids together

There are 2 subunits in ribosome which are?

small and large subunit

3 binding sites

• A site

• P site

• E site

A site

aminoacyl-tRNA arrives

P site

contains tRNA with a polypeptide chain attached to it

E site

empty tRNA exits the ribosome 

Exit tunnel

polypeptide chain leaves the tunnel

Initiation of translation) Small ribosomal subunit binds to what?

mRNA and initiator tRNA

Prokaryotes can bind in either order (T or F)

True

Eukaryotes

• initiator tRNA with Met binds to small ribosomal subunit

• Small ribosomal subunit binds to 5’ cap

• Small subunit moves downstream to start codon

• Initiator tRNA binds to start codon

Large ribosomal subunit binds to small subunit which forms the

translation initiation complex

• Initiation factors - proteins required to bring complex together

• breaks down GTP (Guanosine triphosphate) for energy

Initiator tRNA is in which site

P site

• this determines the reading frame - grouping of bases into codons 

Elongation (stop here)

new amino acids are added to form a polypeptide chain

• proceeds from 5’ to 3’ end of mRNA

• New amino acids are added to the C-terminus of the polypeptide chain

Codon recognition

the anticodon of the next aminoaceyl tRNA binds to the codon of mRNA in the A site

• GTP is broken down to provide energy for this process

peptide bond formation

rRNA catalyzes the formation of the peptide bond between the polypeptide in P site and amino acid in A site

• polypeptide chain is now attached to tRNA in the A site

tRNA in P site moves to _ site and leaves

E

mRNA, tRNA, and polypeptide in A site move to _ site

P

Process uses GTP and ____________ factors

elongation

Elongation continues until a ____ codon is reached

stop

Release factor binds to stop codon in _ site

A

Causes hydrolysis between

polypeptide chain and tRNA in P site