Gene Expression Translation Flashcards

Questions and Answers

What do the letters U, C, A, and G represent in Model 1?

mRNA nucleotides

What do abbreviations such as Phe, Ile, Ala, and Gly represent in Model 1?

Amino acids

What is the significance of the reference to the language of mRNA as a 'triplet code'?

Three nucleotides are needed to code for one amino acid.

If an mRNA molecule had 300 nucleotides in the coding region, how many amino acids would be in the polypeptide synthesized?

100 Signup and view all the answers

How many different codons (triplets) code for the amino acid Proline (Pro)?

4 Signup and view all the answers

What are the similarities and differences among all codons for Proline?

All proline codons start with CC; the difference is in the third base. Signup and view all the answers

What advantage is there for an organism to have multiple mRNA sequences code for the same amino acid?

In case one codon makes a mistake, the mRNA will still translate properly into the amino acid. Signup and view all the answers

Complete the following based on the mRNA codon chart in Model 1: DNA-> TAC CTT CGG ATG CTG ACT; mRNA-> _; polypeptide seq.-> __ .

AUG GAA GCC UAC CAG UGA; met (start) Glu Ala Tyr Gln Signup and view all the answers

What amino acid is at the beginning of every polypeptide according to the table in Model 1?

Methionine (AUG) Signup and view all the answers

What might scientists conclude from the fact that codons shown in Model 1 are used in all species on Earth with very little variation?

All species come from a common ancestor and the theory of evolution. Signup and view all the answers

What are the three stages of translation?

Initiation, elongation, termination. Signup and view all the answers

Define each of the terms used in your answer to part A as they are used in everyday language.

Initiation - to start; Elongation - to make longer, to add on; Termination - to end. Signup and view all the answers

According to Model 2, when the mRNA leaves the nucleus, to which cellular organelle does it attach?

The ribosome. Signup and view all the answers

What is the significance of the sequence AUG, to which the mRNA attaches at the organelle?

AUG is the start codon. Signup and view all the answers

Describe the movement of the ribosome as translation occurs.

The ribosome moves along the mRNA chain from 5 to 3. Signup and view all the answers

What sequence of nucleotides makes the anticodon on the tRNA molecule carrying Histidine (His)?

GUA Signup and view all the answers

What codon on mRNA would match the anticodon GUA?

CAU Signup and view all the answers

What anticodon would be found on a tRNA molecule carrying Glycine (Gly)?

CCA, CCU, CCG, CCC Signup and view all the answers

Explain why tRNA is called transfer RNA.

It transfers the correct amino acid in the correct sequence to the ribosome. Signup and view all the answers

How many tRNA molecules are held in the ribosome during elongation?

2 Signup and view all the answers

What happens to the unattached tRNA once it has delivered the amino acid?

It is released from the ribosome and is free to pick up and carry another amino acid. Signup and view all the answers

Describe two things that occur during termination as illustrated in Model 2.

A release factor binds to the last codon, stopping the addition of amino acids, and a water molecule is added to the end of the amino acid chain. Signup and view all the answers

How does the term 'translation' apply to the synthesis of proteins from the DNA instructions?

The language of DNA, in the form of nitrogen bases read in sets of three called codons, is being translated into proteins, i.e., amino acids. Signup and view all the answers

Show mathematically that there are 64 permutations possible when three bases are used.

4 x 4 x 4 = 64 Signup and view all the answers

Show mathematically that two bases as a codon would not be sufficient to code all 20 known amino acids.

2 x 2 x 2 = 8 Signup and view all the answers

Write a code for an original DNA strand and mutate it so the final protein is unaffected.

Original: TAC AAA CCC GGA; Mutated: TAC AAG CCC GGA Signup and view all the answers

Give two reasons why translation in prokaryotic cells can begin before transcription is finished, unlike in eukaryotic cells.

Eukaryotic cells have a nucleus and prokaryotic cells do not; Transcription occurs in the nucleus while translation occurs in the cytoplasm. Signup and view all the answers

Study Notes

Gene Expression - Translation Overview

The letters U, C, A, and G represent mRNA nucleotides.
Abbreviations like Phe, Ile, Ala, and Gly signify different amino acids.
The "triplet code" nature of mRNA indicates three nucleotides code for one amino acid.

Polypeptide Coding

A mRNA molecule with 300 nucleotides can code for 100 amino acids (300 divided by 3).
Four different codons code for the amino acid Proline (Pro).
All Proline codons start with CC, differing only in the third base.

Genetic Redundancy and Errors

Multiple mRNA sequences coding for the same amino acid provide a backup in case of transcription or replication errors.

mRNA and Protein Synthesis

DNA sequence: TAC CTT CGG ATG CTG ACT translates to mRNA sequence: AUG GAA GCC UAC CAG UGA, leading to polypeptide sequence: Met (start), Glu, Ala, Tyr, Gln.
AUG is the start codon, signaling the beginning of every polypeptide.

Evolutionary Implication

Universal use of codons across all species supports the theory of common ancestry and evolution.

Stages of Translation

Translation consists of three phases: initiation, elongation, and termination.
Everyday meanings:
- Initiation: the beginning of a process
- Elongation: the process of lengthening or adding to something
- Termination: the conclusion or ending of a process

Ribosome Functionality

mRNA attaches to the ribosome after leaving the nucleus.
Ribosomes move along the mRNA chain from 5' to 3' direction.

tRNA's Role

The tRNA carrying Histidine (His) has an anticodon sequence of GUA, which matches the mRNA codon CAU.
Possible anticodons for Glycine (Gly) include CCA, CCU, CCG, and CCC.
Transfer RNA (tRNA) transfers specific amino acids in the correct order to the ribosome for protein synthesis.

Elongation and Termination

During elongation, a maximum of two tRNA molecules can be held in the ribosome concurrently.
Unattached tRNA is released after delivering its amino acid, ready to pick up new amino acids.
Termination occurs when a release factor binds to the last codon, halting further amino acid addition, and a water molecule is added to complete the amino acid chain.

Concept of Translation

"Translation" refers to decoding DNA's nitrogen base sequence (in sets of three, called codons) into the protein language (amino acids).

Codon Combinations

With three bases, there are 64 possible codon permutations (4x4x4).
Only using two bases provides only 8 codon combinations (2x2x2), insufficient for coding all 20 known amino acids.

Silent Mutations and Genetic Structure

An example of a silent mutation: Original DNA: TAC AAA CCC GGA mutated to TAC AAG CCC GGA still produces the same protein.

Differences Between Cell Types

In prokaryotes, simultaneous transcription and translation are feasible due to the absence of a nucleus.
Eukaryotes have distinct transcription (in the nucleus) and translation (in cytoplasm) processes, with introns needing removal from pre-mRNA before translation.

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Test your knowledge on gene expression and translation with these flashcards. Each card covers essential terms and concepts, such as mRNA nucleotides and amino acids. Ideal for students studying molecular biology.