DNA and Protein Synthesis Flashcards

Thirteen practice flashcards covering DNA structure, transcription, splicing, tRNA function, and translation based on lecture notes.

Define genes

A length of DNA with a specific sequence of bases coding for a specific polypeptide to give a specific characteristic.

What is the Non Template Strand?

It is the coding strand which has a sequence of bases corresponding to the base sequence of RNA transcribed.

What are the properties of the Genetic code?

1. Universal, 2. Degenerate, 3. Do not overlap.

How is the term 'Universal' defined regarding genetic codons?

Each codon will code for the same amino acid in different living organisms.

What does it mean for the genetic code to be 'degenerate'?

More than one codon can code for one amino acid because there are $4$ bases arranged in triplets resulting in $64$ different codons coding for $20$ amino acids, which may lead to silent mutation.

Explain what is meant by the genetic code property 'Do not overlap'.

No base from one triplet enters to be a part of an adjacent triplet.

Briefly define the process of transcription.

It takes place inside the nucleus, where a gene on DNA is transcribed into mRNA.

What are the major steps that occur during transcription?

1. Part of the DNA unwinds/unzips due to the break down of hydrogen bonds by RNA polymerase 2. The non coding strand acts as the template strand where the free activated RNA nucleotides are added along the side of the template strand (from the 5' to 3' direction) according to the complimentary base pairing rule 3. The free activated nucleotides are joined together by the RNA polymerase forming phosphodiester bonds 4. Primary transcript is spliced by spliceosome enzyme which removes the non coding parts (introns) and joins the coding parts (exons) 5. The mature mRNA leaves the nucleus through the nuclear pores in the nuclear envelope to the ribosomes in the cytoplasm

Describe the function of the spliceosome enzyme.

The spliceosome is an enzyme that removes the non coding parts (introns) and joins the coding parts (exons) to form mature mRNA Same spliceosome can join exons in different arrangements Single gene can produce several versions of functional mRNA coding for different sequences of amino acids. So single gene can code for different polypeptides in the same protein or different protein

What is tRNA

It is the site where a specific amino acid is attached under the control of a specific enzyme using energy from ATP, forming a tRNA amino acid complex

What is the function of tRNA during protein synthesis?

tRNA carries a specific amino acid to the ribosome Where the tRNA has anticodons that pair up with its corresponding codon on the mRNA Where temporary hydrogen bonds form, ensuring the correct amino acid sequence in polypeptide chain

Describe the process of translation

1. mRNA attaches to the small ribosomal subunit exposing 6 bases (2 codons) at a time to large ribosomal subunit 2. tRNA carries a specific amino acid to the ribosome, and the tRNA has anticodons that pair up with the corresponding codons on the mRNA, where they bind together by temporary hydrogen bonds, another tRNA brings another specific amino acid to the ribosome 3. tRNA brings two amino acids close together allowing the formation of peptide bonds by condensation reaction catalysed by the peptidyl transferase enzyme in the large ribosomal subunit 4. Stop codon (UAG, UAA, UGA) which do not code for an amino acid terminate the translation 5. Formed peptide chain enters the rough endoplasmic reticulum for modification NOTE : The tRNA can be reused to bring another amino acid NOTE : several ribosomes can attach to the same mRNA at the same time Polyribosome, thus producing several identical polypeptides at the same time from one mRNA ( mass production )

What is the role of the ribosome during translation?

1. Provides an attachment site for two tRNA at a time where two amino acids are brough close together allowing the formation of a peptide bond by condensation reaction catalysed by peptidyl transferase 2. Assembles amino acids into a primary structure 3. Ribosomes move along the mRNA

Describe what happens during semi conservative replication of DNA

1. Double helix unwind

2. Helicase enzyme breaks down hydrogen bonds between complementary nitrogenous bases, forming replication fork

3. Activation of free nucleotides by adding 2 extra phosphate groups

4. Both strands act as template strands, where activated nucleotides pair up with complementary base on each DNA strand

5. DNA polymerase

• add activated nucleotides one by one to the new growing DNA strand according to the complimentary base pairing rule in 5’ to 3’ direction only

• Forming phosphodiester bonds between the adjacent nucleotides / formation of polynucleotide

• Where the leading strand is formed continuously from 5’ to 3’

6. While the lagging strand from 3’ to 5’

• its formed by DNA polymerase forming Okazaki fragments from 5’ to 3’

• Then ligase enzyme responsible for the formation of phosphodiester bond between the Okazaki fragments joining them together on the lagging strand

7. The process will continue along the DNA molecule

8. Producing 2 identical DNA molecules by semiconservative replication, newly DNA molecule is formed has one old strand (parental) and another new strand