Bio 011 Midterm 2 CHP 12

codon

In bacteria transcription and translation occur together in the

cytoplasm

In eukaryotes, transcription occurs inside the

nucleus

If DNA is the template what is the process and the product

????

In eukaryotes, translation occurs inside the

ribosomes

If DNA is the template what is the process and the product

(Process: The action or how it gets made)

(Product: The final result or what gets made)

Process: transcription

Product: Pre-mRNA

If Pre-mRNA is the template what is the process and the product

(Process: The action or how it gets made)

(Product: The final result or what gets made)

Process: Splicing

Product: mRNA

If mRNA is the template what is the process and the product

(Process: The action or how it gets made)

(Product: The final result or what gets made)

• Process: Translation

• Product: Protein

when it comes to the central dogma, What are the differences in

prokaryotes vs. eukaryotes?

In prokaryotes, transcription and translation occur simultaneously in the cytoplasm without RNA processing. In eukaryotes, transcription and RNA processing (5' capping, splicing, polyadenylation) occur in the nucleus, followed by translation in the cytoplasm.

what are the 3 Stages of Transcription

Initiation, Elongation, Termination

Initiation (The Start)

RNA polymerase and a helper protein called sigma factor lock onto a specific starting spot on the DNA called the promoter.

Elongation (The Build)

Sigma factor leaves, and RNA polymerase slides down the DNA template, building the new mRNA strand in the 5' to 3' direction.

Termination (The Finish)

RNA polymerase hits the terminator sequence, causing the enzyme, DNA, and newly made mRNA to all let go and separate.

Modifications to Eukaryotic pre-mRNA functions

1. facilitate export to

cytoplasm

2. prevent degradation

3. help ribosomes attach

to mRNA

types of Modifications to Eukaryotic pre-mRNA functions

5’ Cap

• poly-A tail

why do eukaryotes need a 5'Cap and a poly-A tail (Only in EUK)

they prevent the degradation ensuring that mRNA survives long enough to be translated into protein

why do Spliceosome cuts out

introns

Introns are non-coding segments interrupting the gene sequence

Telomerase uses an ________________ to add telomere repeats. This avoids chromosome shortening

after each round of replication.

RNA template and DNA synthesis activity

At the molecular level, the central dogma states

most genes are transcribed into mRNA and the mRNA is then translated into protein

5' Cap Addition

A modified guanine nucleotide (7-methylguanosine) is added to the front ($5'$) end of the pre-mRNA transcript.

poly-A tail

A long chain of adenine ("A") nucleotides is added to the back ($3'$) end of the transcript

An RNA copy of a gene is produced via the process of

transcription

n RNA molecule that catalyzes a chemical reaction is called a(n) _______

ribozyme

The transcription of non-coding RNAs can produce two important products: [Field 1] RNA and [Field 2] RNA.

• Field 1: transfer (or tRNA)

• Field 2: ribosomal (or rRNA)

Describe how a

eukaryotic pre-RNA

molecule is modified:

a) At the ends

b)In the middle

Pre-mRNA is modified at the 5' end with a 7-methylguanosine cap, at the 3' end with a poly-A tail (both for stability, export, and translation), and in the middle via RNA splicing where non-coding introns are removed and coding exons are joined.

starts at a promoter and ends at a terminator sequence.

RNA polymerase

RNA polymerase always starts at a

promoter

How does RNA polymerase know where to start and stop transcription?

It starts by recognizing specific DNA sequences called promoters (helped by transcription factors), and it stops when it encounters a terminator sequence that causes the enzyme to detach and release the RNA transcript.

What is removed from a pre-mRNA by a spliceosome?

Non-coding intervening sequences called introns are cut out and degraded, while the coding sequences (exons) are joined back together to form the mature mRNA.

What is included in a mature mRNA?

A 5' cap, a 5' untranslated region (UTR), protein-coding sequences made of joined exons, a 3' UTR, and a 3' poly-A tail (with all introns completely removed).

What is a codon? How many codons are there?

A codon is a sequence of three consecutive nucleotides on an mRNA molecule that codes for a specific amino acid (or a stop signal). There are 64 total codons: 61 code for amino acids, and 3 serve as stop codons.

Spliceosome

cuts out introns

what event occurs after spliceosome cut out introns?

alternative splicing—a process where different combinations of exons are joined together to create multiple unique mRNA variations (and thus different protein isoforms) from a single gene.

What is needed to synthesize a protein? (The machinery of translation)

mRNA, RIbosome, tRNA

How does the genetic code specify the relationship between mRNA sequence and amino acid sequence in a polypeptide?

The genetic code is a triplet code where every sequence of three nucleotides (codons) on the mRNA is read sequentially by tRNA anticodons, translating each codon into a specific amino acid (or a stop signal) to build the polypeptide chain

What is the function of transfer RNA (tRNA)?

tRNA acts as a translator matchmaker: its anticodon locks onto the matching codon on the mRNA, dropping off the exact amino acid needed for the growing protein chain.

How are tRNAs made and matched with the correct amino acid?

They are made by being transcribed from DNA genes, and they are matched (charged) with their correct amino acid by matchmaker enzymes called aminoacyl-tRNA synthetases using cellular energy.

Based on the genetic code, each of the 64 codons specifies either a_________, other _______, or a _____ codon

start codon (methionine), amino acids (including methionine after

the start), stop codon

The template strand of DNA is “read” by RNA polymerase to make

mRNA containing codons

The coding strand of DNA contains the

same ______sequence of codons found in the _____

5’ – 3’, mRNA

what requires mRNA, tRNA and ribosomes

translation

The enzyme _________attaches the correct amino

acid to a tRNA molecule.

aminoacyl-tRNA synthetase

How many different aminoacyl-tRNA synthetases do you predict?

There are 20 different synthetases—one for each standard amino acid—because each enzyme is uniquely dedicated to attaching its specific amino acid to its corresponding tRNA.

What are the two primary macromolecular components that make up a ribosome subunit?

proteins and ribsomal RNA

What are the sedimentation coefficients of bacterial ribosomes and their subunits?

Bacterial ribosomes are 70S, composed of a 30S small subunit and a 50S large subunit

Where are eukaryotic ribosomal subunits assembled?

nucleolus of the nucleus, after which they are exported into the cytosol

What are the three discrete functional sites on a ribosome where tRNAs bind during translation?

The A site (aminoacyl site), P site (peptidyl site), and E site (exit site)

What is the function of the initiation stage of translation?

: It assembles the mRNA molecule, the initiator tRNA, and both ribosomal subunits into a proper complex to position the first tRNA at the start codon in the P site.

What is the function of the elongation stage of translation?

It's the "building" phase. The ribosome slides down the mRNA chain, matching incoming tRNAs to codons, forming peptide bonds, and adding amino acids one by one to grow the polypeptide chain

What is the function of the termination stage in translation?

It's the "stop and release" phase. When a stop codon is reached, a release factor steps in to split apart the complex, freeing the newly completed protein and the machinery.

What is the significance of a reading frame in translation?

It determines how mRNA nucleotide sequences are grouped into nonoverlapping codons (sets of three bases).

What is a ribozyme?

Its function is to hydrogen-bond with the small ribosomal subunit, helping position and bind the mRNA to the ribosome so that translation can begin near the start codon.

What are the core similarities between bacterial and eukaryotic translation?

Both use the exact same three stages (initiation, elongation, termination) and synthesize polypeptides in the 5' to 3' direction along the mRNA.

What are the key differences between bacterial and eukaryotic translation?Definition (Answer):

• Ribosomes: Bacteria use 70S; eukaryotes use 80S.

• Start Signal: Bacteria use a ribosomal-binding site; eukaryotes use a 5' cap and Kozak rules.

• First Amino Acid: Bacteria use formyl-methionine; eukaryotes use regular methionine.

• Termination Factors: Bacteria use two factors (RF1 and RF2); eukaryotes use one (eRF).

Each 3 nucleotide codon codes for a

specific amino acid

How many different

tRNAs are there?

Between 20 and 61

amino acids are added one at a time to the

C-terminus of the growing polypeptide

elongatio

occurs when release factor binds to a stop

codon

termination

Which of the following in NOT a property of the genetic code?

It determines the rate of transcription.

Which of the following is not involved in the initiation of translation?

RNA polymerase

Formation of a peptide bond during translation elongation is catalyzed by:

Ribozyme activity of the ribosomal RNA

What recognizes the codons UAA, UAG, UGA in the ribosome "A" site?

release factor protein

A difference between bacterial and eukaryotic translation is

modifications to the 5’ end of mRNA are required for ribosome binding only in eukaryotes

RNA interference (miRNAs and siRNAs) is a mechanism for silencing gene expression at the:

post-transcriptional (after transcription) but pre-translational (before translation) level

To which of the following types of molecules could an non-coding RNA (ncRNA) bind?

protein

DNA

other RNA

Which of the following is NOT a general function of an non-coding RNA (ncRNA)?

encoding polypeptides

How is DNA synthesis on the leading strand vs. lagging strand different?

leading strand is continuous, Lagging strand has discontinuity through oka fragments,

stages of translation

Intiation then Elongation the Termination