BIO 190- Ch #10 *The Expression of Genetic Info via Transcription and Translation

Describe how transcription is different in bacteria compared to eukaryotes

Bacteria: mRNA is translated while it is being transcribed they are coupled

Eukaryotes: mRNA must be exported from nucleus to be transported

central dogma

DNA -> transcription--> RNA -> translation --> Protein

what do genes do

provide the blue print for the characteristics of organisms

the code to make protein is embedded in the DNA in nucleotide sets called what

codons

mRNA

messenger RNA; type of RNA that carries instructions from DNA in the nucleus to the ribosome

Transcription

the process of creating mRNA from a DNA template

DNA serves as the template

RNA polymerase reads DNA __________' and builds mRNA _________', and _______ replaces thymine in mRNA.

RNA polymerase reads DNA 3' to 5' and builds mRNA 5' to 3', and uracil replaces thymine in mRNA.

what strand does mRNA use and what does it ignore

The DNA strand that is used as a template for mRNA synthesis is called the template strand

The DNA strand that is not used is the coding strand

mRNA is _____________ and _________ to the bottom DNA strand

complementary and antiparallel

transcription vs translation

transcription: a gene in the DNA is copied into messenger RNA (mRNA) inside the nucleus. This mRNA acts like a message that carries the instructions for making a protein.

translation, the mRNA travels to a ribosome in the cytoplasm, where it is read in groups of three bases called codons. Each codon tells the ribosome which amino acid to add next, and the amino acids are linked together to form a protein

transcription writes the message, and translation builds the protein.

what is transcription

- DNA is copied into mRNA

- RNA polymerase binds to a a gene on DNA and builds its complimentary strand (A--> U) (C-->G)

- In eukaryotes RNA processing modifies the mRNA by removing the introns, keeping the exons (splicing them together)

- 5 cap and poly tail are added for protection

-mRNA goes off the cytoplasm

Describe what allows the DNA to be transcribed into RNA

promotor:

Transcribed region:

Terminator:

Regulatory sequence:

promotor: where RNA polymerase binds

Transcribed region: info that specifies an amino acid sequence

Terminator: signals the end of transcription

Regulatory sequence: determines rate that RNA polymerase binds

Transcription occurs in what 3 stages

1. Initiation: promotor is recognition site, RNA polymerase binds, DNA strands are separated

2. Elongation: RNA polymerase reads template strand 3' to 5'

RNA polymerase synthesizes transcript 5' to 3'

3. Termination: RNA polymerase reaches a terminator and dissociates

RNA polymerase reads template strand _________

RNA polymerase synthesizes transcript _____

3' to 5'

5' to 3'

template vs coding strand during transcription

template strand (bottom) is used to read by RNA pol in 3' to 5'

the coding strand (top) is ignored

during transcription what helps RNA polymerase find its gene promotor

sigma factor

what strand does RNA polymerase "push away"

the coding strand (initiation)

after RNA polymerase clears the promotor what happens

the transcribed DNA zips back together

RNA polymerase is released and can go back to the promotor to transcribe again

mRNA vs coding strand

mRNA has the same sequence (5' to 3') and 5'-3' direction as the coding strand expect U replaces T

pre-mRNA must go through what 3 processes before exiting through a nuclear pore

1. splicing

2. capping

3. poly A tail

what is splicing of pre-mRNA

Removing non coding regions aka introns from RNA and seals exons together

what is capping of pre-mRNA

when a modified form of guanine is attached to the 5' end

the 5' cap is recognized by a variety of proteins it is needed for mRNA to exit the nucleus and bind the ribosome

what is the poly A tail

added to the 3' end after transcription it increases the stability of the mRNA in the cytosol

what is translation

the decoding of an mRNA message into a protein

what is the genetic code

specifies the relationship between the sequence of nucleotides in the mRNA sequence of amino acids in a polyepeptide, the code is read in groups of 3 (codons)

codons

The three-base sequence of nucleotides in mRNA

how many codons are there start vs stop

1 start and 3 stop

what does the redundantcy of codons mean

The redundancy of codons means that more than one codon can code for the same amino acid.

This redundancy helps protect against mutations, since a change in one base might still result in the same amino acid being made.

what are 4 key components during translation

ribosomal binding site, start codon, coding sequence, and stop codon

what is the start codon

AUG

what is the coding sequence

the sequence of nucleotides in mRNA that encode amino acids. The start codon is the start of the coding sequence and the stop codon is the end of the coding sequence.

what brings the amino acids to the ribosome during translation

transfer RNA

tRNAa contain ________ that is complimentary to an mRNA codon

anticodon

anticodon

group of three bases on a tRNA molecule that are complementary to an mRNA codon

why does translation take energy

Translation takes energy because building a protein is a complex and active process that requires multiple steps, all of which need energy to happen efficiently and accurately.

what are the sites of translation

ribosomes

what are the 3 sites where tRNA acts on a ribosome

A site: where tRNA enters ribosome

P site: tRNA slides from A site to its amino acid removed/added to growing polypeptide

E site: empty tRNA exits

does bacteria have a 5 cap

no

describe elongation

-RNA polymerase assembles the RNA nucleotides that complement the template strand of DNA

-after the RNA polymerase copies part of the strand, the copied part of the DNA joins back together

when does termination occur during translation

when a stop codon is read , they are recognized by a release factor not tRNA

during transcription _____ is used as a template to make ________

DNA; RNA

During translation the information within the _______ is used to make _____

mRNA; polypeptide

when does the sigma factor cause the binding of RNA polymerase to the promotor sequence

during bacterial initiation of transcription

sigma factor is not found in eukaryotes

A region of the template strand of DNA used for transcription is

3'-AGCTTGAG-5'. What sequence of RNA would be transcribed from this region?

5' - UCGAACUC-3'

RNA is complementary and antiparallel

splicing of pre-mRNA involves the

removal of introns and connection of exons

is a eukaryotic mRNA failed to have a cap attached to its 5' end what would 2 negative consequences be

the mRNA would not properly exit the nucleus and it would not properly bind to a ribosome

once a molecule of RNA polymerase transcribes a gene what happens to it

it goes back to the promotor of the gene to transcribe the gene again

aminoacyl-tRNA synthetase

has binding sites for a specific amino acid, specific tRNA and ATP

where will translation begin on mRNA

on the first AUG codon found AFTER the ribosome binding site

Name key differences in eukaryotic translation initiation compared to prokaryotic

- In eukaryotes, the 5' cap on mRNA is essential for the binding of the mRNA to the small ribosomal subunit.

- The start codon selection in eukaryotes depends on the Kozak sequence around the AUG, which helps the ribosome find the correct start site.

-The initiator tRNA in eukaryotes carries methionine (Met), whereas in bacteria it carries formyl-methionine (fMet).

- Eukaryotic mRNA must be exported from the nucleus to the cytosol before translation can occur.

List correct features of gene expression

- In a multicellular organism, all genes are present in every nucleus, but some of these genes will never be expressed.

- In a multicellular organism, all genes are present in every nucleus, and some of these genes will be transcribed into mRNA in some cells, but not in others.

- the production of mRNA and translation of that mRNA into protein is called Gene Expression.

-Some genes are expressed at all times, in all cells, but other genes only produce mRNA at certain points in the life of a cell or in response to certain conditions.

-Genes that do not produce mRNA and do not contribute to the phenotype are "not being expressed."

amino vs carboxyl end

amino end = first amino acid

The carboxyl (C-) end is where the last amino acid goes