Ch. 17 Transcription and RNA Processing

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Proteins are ___ made up of ___

Proteins are ___ made up of ___

Proteins are polypeptides made up of amino acids

What links amino acids?

Peptide bonds

Gene expression

the process by which DNA directs the synthesis of proteins

What are the 2 stages of Gene Expression?

What organisms does it occur in?

Transcription & Translation

Occur in all organisms

Transcription

What does is allow for?

the synthesis of RNA

uses info from DNA

Allows for “message” of the DNA to be transcribed

Where does Transcription occur?

In the nucleus- Eukaryotic

In the nucleoid region- Prokaryotic

Translation

What does Translation change?

The synthesis of a polypeptide

Uses info from RNA

A nucleotide sequence becomes an amino acid sequence

Where does Translation occur?

Ribosome

What are the 3 Types of RNA?

1. Messenger RNA (mRNA)

2. Ribosomal RNA (rRNA)

3. Transfer RNA (tRNA)

How is Messenger RNA formed?

It is synthesized during transcription using a DNA template

What is the function of Messenger RNA

Messenger RNA carries info from the DNA (nucleus)→ ribosomes (cytoplasm)

What is Transfer RNA used for?

Translation

Each tRNA can carry?

A specific amino acid

What does Transfer RNA attach to?

How does it attach?

Attaches to mRNA

attaches using their anticodon

Complements mRNA’s codon

What does Transfer RNA do?

Allows information to be translated into a peptide sequence

What does Ribosomal RNA do?

Helps form ribosomes

Helps link amino acids together

DNA contains what that codes for proteins

A sequence of nucleotides that codes for proteins

How is the sequence of nucleotides read?

What is it called?

Read in groups of 3

Called the triplet code

During ___ only 1 ___ strand is being transcribed

During transcription

Transcribes 1 DNA strand

Alternate names for DNA strand in transcription

Template strand

Noncoding strand

Minus strand

Antisense strand

mRNA molecules formed are ___ & ___ to the DNA nucleotides

They are antiparallel & compliementary to the nucleotides

Base pairs

A→ U

C→G

mRNA nucleotide triplets are called?

codons

How many different codon combinations?

64

How many codons code for amino acids?

61

How many codons are stop codons?

3

Why are codon’s considered to be Redundant?

Because more than one codon can code for each amino acid

Codon’s are considered to be what to life?

Universal to all life

Reading frame

The codons on the mRNA must be read in the correct groupings during translation to synthesize the correct proteins

Why is the reading frame so important?

It is important because if the reading frame shifts even by one letter it will produce a completely different outcome

List the 3 steps in Transcription

1. Initiation

2. Elongation

3. Termination

Describe Initiation

RNA Polymerase binds to the promoter region on DNA

Does not need a primer

Where are promoter regions?

They are always upstream of the desired gene to transcribe

How does Initiation differ in Eukaryotes?

The promoter region is called the TATA box

Transcription factors help RNA polymerase bind

How does Initiation differ in Eukaryotes?

RNA polymerase binds to promoter region (TATA BOX)

Transcription factor help RNA polymerase bind

Describe Elongation

Opens the strand

Polymerase moves downstream 3’→5” and pairs RNA molecules to DNA molecules

As the growing mRNA strand peels away from DNA template strand → DNA double helix reforms

In what direction does mRNA transcript enlongate?

5’ → 3’

What can increase the amount of mRNA synthesized and proteins produced?

a single gene can be transcribed simultaneously by several RNA polymerase molecules

increases the amount of mRNA synthesized and protein production

Describe Termination

Once polymerase reaches the end the mRNA molecule is removed and the double stranded helix is form back together

How does Termination differ in Prokaryotes?

• Transcription proceeds through a termination sequence- causes a termination signal

• RNA polymerase detaches

• mRNA transcript is released & goes to translation (ribosomes)

  mRNA does NOT need modifications

How does Termination differ in Eukaryotes?

• RNA polymerase transcribes a sequence of DNA (polyadenylation signal sequence)

• Codes for a polyadenylation signal ( AAUAAA)

• Releases the pre-mRNA from the DNA

  must undergo modifications before translation

What are the 3 modifications that must occur to Eukaryotic pre-mRNA before it is ready for translation

1. 5’ cap

2. Poly-A tail

3. RNA splicing

What is the 5’cap (GTP) modification? (pre-mRNA)

The 5’ end of the pre-mRNA receives a modified guanine nucleotide “cap”

What is the Poly-A tail modification? (pre-mRNA)

The 3’ end of the pre-mRNA receives 50-250 adenine nucleotides

BOTH the 5’ cap and the poly-A tail function to?

• Help the mature mRNA leave the nucleus

• Help protect the mRNA from degradation

• Help ribosomes attach to the 5’ end of the mRNA when it reaches the cytoplasm

What is RNA Splicing modification? (pre-mRNA)

sections of the pre-mRNA(introns) are removed

the exons join together

Introns

intervening sequence

DON’T code for amino acids

Exons

expressed sections

code for amino acids

Why does splicing occur?

A single gene can code for more than 1 kind of polypeptide

AKA alternative splicing

Why does the pre-mRNA have to undergo modifications?

Once all modifications have occured, the pre-mRNA → mature mRNA

the mature mRNA can leave the nucleus → cytoplasm for translation at the ribosomes