Mod 12: Transcription and Translation

What is transciption?

synthesis of RNA from a DNA template

What is translation?

synthesis of proteins from mRNA

How many strands does DNA have?

2

What do genes contain?

genetic information to code for proteins

"About […] of DNA is coding."

1-2%

"Majority of DNA is considered […]."

non-coding

Genes on their don't have a …

function

"The information in genes must be […]."

transcribed

The information in genes relative to the nucleus, must be …

transported out of the nucleus

When is mRNA utilized?

during transcription

What is mRNA used for?

to transfer information in a gene to the nucleus to create proteins

how many strands does DNA have?

2

The coding strand of DNA contains…

the desired sequence of nucleotides

What direction is the DNA coding strand?

5' to 3'

what is the template strand of DNA?

the strand that RNA or DNA polymerase reads to build a new strand

How can the template strand be described?

complimentary, yet antiparallel to nucleotides

What direction is the template strand?

3' to 5'

What is RNA polymerase?

an enzyme responsible for production of mRNA from DNA

How does RNA unwind and rewind DNA?

by acting like a helicase

what does RNA polymerase catalyze?

ester bonds between nucleotides

What molecule are the RNA building blocks?

ribonucleoside triphosphates

What does RNA polymerase do to ribonucleoside triphosphates?

links them together during transctiption to make RNA strand

How does RNA polymerase get its energy for polymerization?

by cleaving the high energy phosphate bonds 

How many types of RNA polymerase do humans have?

3

What are the types of RNA polymerase?

1. RNA polymerase I 

2. RNA polymerase II

3. RNA polymerase III

RNA polymerase I produces …

most rRNA

RNA polymerase II produces …

produces mRNA

RNA polymerase III produces …

tRNA and other small RNA molecules

What are promoters?

a sequence of DNA located just before a gene

What do promoters help RNA do?

recognize where DNA should be transcribed

What is a transcription factor complex?

a group of proteins that join together on DNA to act as an on/off switch for a specific gene

What does transcription factor complex binds to?

enhancer and promoter regions

what are enhancer regions?

dna sequences that tell a gene when and where to work, and how much protein to make (act like a volume knob for genes)

What can enhancer and promoter regions be bound by?

RNA polymerase

What does the sequence of DNA play a role in?

identifying sequence for transcription

Does the sequence do more than code for proteins?

yes

what is pre-mRNA?

the initial mRNA transcript

what happens to the mature mRNA transcript?

its exported to the cytosol for translation into a protein

Does the pre-mRNA have to processed first?

yes

the mature mRNA is …

capped

where is the mRNA capped?

at the 5' end with a nucleotide

Why is the mRNA transcript capped?

to prevent degradation of the mRNA molecule 

what does capping mRNA promote?

translation

what is the poly(a) tail?

a protein binding site 

what does the poly(a) tail promote?

translation into a protein

What does the poly(a) tail protect?

mRNA from degradation

where is a poly(a) tail added?

to the 3' end of the transcript

What happens when a stop codon appears during transcription?

"a ""tail"" of adenosine molecules is added on"

how long can a poly(a) tail be?

>200 nucletides in length

what are introns?

non-coding sections of DNA and RNA found within a gene

What happens to the introns during transcription?

they are removed from the mature mRNA molecule

What are exons?

the section in the mRNA that contain the instructions for building proteins

What happens to the extrons?

they are spliced together

what do the exons forn?

the appropiate code for the protein amino acid sequence

what are exons?

sections of a gene that contain instructions for building

what do exons form?

appropiate code for the protein acid sequence.

what does mRNA provide the blueprint for?

tRNA and ribosomes to make real life proteins

what is a codon?

every 3 nucleotides of the mRNA message

What does each codon correspond to?

a specific amino acid to be added to the polypeptide chain

What is a degenerate?

multiple 3 letter nucleotide combinations (codons).

What can degenerate codons code for?

the exact same amino acid

What is a unambiguous codon?

a codon that codes for only one amino acid

what is the Wobble Hypothesis?

explains how one tRNA molecule can recognize multiple mRNA codons

What is the start codon?

AUG

What is the start codon involved in?

initiation of translation 

what does the start codon set?

the reading fram

there are no extra … in the mRNA code.

nucleotides

how many times is each codon read?

once

do the codons overlap?

no

how are codons read and translated?

sequentially.

codons are read until they encounter a …

stop codon

which codons are stop codons?

UAG, UGA, UAA

what is the stop codon near?

the 3' end of the mRNA molecule

What does damaged or mutated DNA result in?

a spectrum of errors in protein production

what are point mutation?

a single base error

What are the 3 points mutations?

1. silent mutation

2. missense mutation

3. nonsense mutation

What are silent mutations?

the incorrect base codes for the same amino acid 

what is an example of silent mutations?

CGA and CGG both code for arginine

What are missense mutations?

the incorrect base codes for a different amino acid

what is an example of missense mutations?

CGA --> CCA results in proline instead of arginine

What are nonsense mutations?

the incorrect base produces a stop codon

What do nonsense mutatons result in?

termination of translation from that point on

What other kinds of mutations may occur?

insertions, deletions, and frameshift mutations

Insertion and deletion mutations

extra nucleotides are added or existing ones are removed from DNA sequence

What are frameshift mutations?

insertion or deletion causes a shift in the reading frame

what do frameshift mutations significantly alter?

the amino acid sequence of the resulting protein

what is tRNA?

a small RNA moleucle that acts as bridge between genetic codes and proteins

What is aminoacyl-tRNA?

tRNA that is covanlently bonded to its matching amino acid

where is aminoacyl-tRNA bonded?

at the 3' end

each tRNA molecule has a specific … 

anticodon region

what does the anticodon region of tRNA do?

recognize a specific codon on mRNA

what is an example of a tRNA anticodon?

the CGU anticodon of alanyl-tRNA recognizes the GCA codon of mRNA

What are the 3 steps of translation?

1. initiation

2. elongation

3. termination

what is translation initiation?

first phase where of protein synthesis

what does translation initiation involve?

a ribsoome assemebles around a messenger RNA (mRNA) molecule and the first transfer RNA (tRNA).

what specifically interacts during initiation?

the mRNA 5' cap with the ribosomal subunit, and the aminoacyl-tRNA

which aminoacyl-tRNA is involved with initiation?

methionyl-tRNA

what does the initiation complex do?

scans the code until the start codon is encountered

What does the large ribosomal subunit do?

joins the small subunit during initation after the complex scans the code. 

what is elongation relative to protein synthesis?

the second and largest phase