BIOKEEN SES 2023/2024 C5

BioKEEN
CHAPTER 5
EXPRESSION OF BIOLOGICAL INFOMATION

​Concept was called the central dogma by Francis Crick in 1956.
Our genome operates by sending info from double-stranded DNA in the nucleus, via single-stranded mRNA, to guide the synthesis of proteins at ribosomes in the cytoplasm.

CENTRAL DOGMA

• Process of copying a DNA molecule before a cell divides.

• Occur during the S or synthesis phase of interphase.

• Begins at a specific site in the DNA called the origin of replication.

• Two strands open forming Replication Forks (Y-shaped region)

• New strands grow at the forks.

• DNA replication is bidirectional from the origin of replication (but will consider events at just one replication fork)

DNA REPLICATION

Multiple Choice

1. Which of the following statements about the newly synthesized DNA molecule is correct?

• It consists of two new DNA strands

• 1. It consists of one new strand and one strand of the original DNA molecule.

• 1. It consists of two strands that are made up of a mixture of new and original nucleotides.

• 1. The sugar-phosphate chains are conserved and new bases are inserted

The process consist of six enzymes and one protein

DNA REPLICATION

DNA REPLICATION

● Helicase unwind the double helix DNA and double stranded DNA is separated

● Each strand act as a template

● Single strand binding protein bind to single-stranded DNA (to prevent them from rejoining)

● When DNA is unwound, it becomes more twisted / supercoiling

● Topoisomerase relieve the strain of twisted DNA

● Primase synthesized RNA primer by adding complementary RNA nucleotide

● DNA polymerase III adds complementary DNA nucleotide to the 3’ end of RNA primer

● Replication / elongation occurs from 5’ to 3’ direction

● The leading strand is synthesized continuously towards replication fork

● The lagging strand is synthesized away from replication fork Forming Okazaki fragments

● DNA polymerase I replace RNA primer with DNA nucleotide

● DNA ligase joins the Okazaki fragments

● Two identical copies of original / parental DNA is produced

Multiple Choice

During step 1: Separation of DNA double helix. The enzyme _______ binds to origins cause the DNA double helix to unwind. The hydrogen bond between the nitrogenous bases break causing DNA strand to separate.

• Topoisomerase

• Primase

• DNA Ligase

• Helicase

Multiple Choice

___________ bind to the separated DNA strands and prevent them from rejoining. Then bind and relieves strain due to supercoiling of DNA molecule.

• Topoisomerase

• Primase

• DNA Ligase

• Helicase

Multiple Choice

During step 2: Building a primer. Enzyme ______ catalyzed the synthesis of a short RNA primer and used as the primer for DNA synthesis.

• Primase

• DNA Ligase

• DNA Polymerase I

• Topoisomerase

Multiple Choice

During step 2: Building a primer. Enzyme ______ catalyzed the synthesis of a short RNA primer and used as the primer for DNA synthesis.

• Primase

• DNA Ligase

• DNA Polymerase I

• Topoisomerase

Multiple Choice

During step 3: Assembling complementary strands. ________ bind and catalyze the synthesis of a new DNA strand by adding DNA nucleotides to the RNA primer.

• Primase

• DNA Ligase

• DNA Polymerase III

• Topoisomerase

Multiple Choice

DNA synthesis in continuous manner towards the replication fork is called

• leading strand

• lagging strand

• lag strand

• lead strand

Multiple Choice

_________ remove RNA primers and replaced by DNA nucleotide.

• Primase

• DNA Polymerase I

• DNA Ligase

• Topoisomerase

Multiple Choice

________ catalyzes the formation of a phophodiester bond between two Okazaki fragments.

• Helicase

• DNA Polymerase I

• DNA Ligase

• DNA Polymerase III

• The process by which genetic information contained in DNA is transcribed into mRNA.

• Takes place in cell nucleus

• Enzyme involved is RNA polymerase

TRANSCRIPTION

PROCESS OF TRANSCRIPTION

● Elongation occurs in the direction of 5’ to 3’ end

● A DNA-RNA hybrid is temporarily formed

● Elongation proceeds until RNA polymerase reaches termination site

● RNA polymerase stop adding nucleotides to the RNA strand

● mRNA is synthesized / produced

● mRNA molecule is released / detaches from DNA template

● The double stranded DNA recoil into double helix again

● RNA polymerase binds to promoter on DNA

● It unwinds the double helix DNA

● It breaks the hydrogen bonds between complementary nitrogenous bases

● Both DNA strands are separated (at a specific points along the length)

● Only one of DNA strand is used as a template

● RNA polymerase add a free ribonucleotide which are complementary to

the bases on the DNA template strand

● Cytosine pairs with Guanine and Adenine pairs with Uracil

Multiple Choice

What is the relationship between strands of RNA and DNA in transcription?

• 1. unrelated

• an exact duplication

• 1. complementary

• one longer than the other

Multiple Choice

A promoter is best described as

• 1. A substance which facilitates RNA transcription

• 1. A sequence of bases at which RNA polymerase begins transcription

• 1. A type of RNA which promotes cell division

• An environmental change which causes transcriptional to occur

• The process of translation the genetic information in mRNA into sequence of amino acids in a polypeptide chain during protein synthesis.

• Occur in cytoplasm.

• Involved 3 types of RNA

TRANSLATION

Fill in the Blank

Carry genetic information transcribed from DNA in nucleus to ribosomes for translation in cytoplasm.

Fill in the Blank

Sites of translation and combines with protein to form ribosomes of 2 subunits in the cytoplasm.

Fill in the Blank

Transfer specific amino acids to the ribosome during synthesis of polypeptide.

Multiple Choice

1. Which of the following are TRUE about the genetic code?

   1. I. All 64 triplet codes on DNA codes for one amino acid

   2. II. Codon AUG on mRNA is usually the start code for protein synthesis

   3. III. Codon UGA, UAA and UAG are stop codes for protein synthesis

   4. IV. Genetic code is degenerate

• I, II and III

• 1. I, II and IV

• 1. II, III and IV

• 1. I, II, III and IV

Fill in the Blank

Based on figure below, name the enzymes involved

Multiple Choice

1. Which one is not a function of RNA?

• 1. Carrying genetic information from DNA molecule to ribosomes

• Carrying amino acids to ribosome

• As a main component of ribosomes

• 1. Transmitting genetic information from cell to cell.

Multiple Choice

1. If the DNA triplets are GTT ACG, the tRNA anticodons would be…

• GTT ACG

• ATG CGT

• 1.  CAA UGC

• GUU ACG

Multiple Choice

Which of the following is false

• 1. RNA Polymerase attaches to DNA at the origin site

• RNA molecules are products of transcription

• 1. Protein are translated in the cytoplasm

• 1. Histones are found only in eukaryotic chromosomes.

Multiple Choice

1. A segment of a certain polypeptide chain in an enzyme is made up of the following amino acid sequence. 

….– ile – pro – ser – pro – cys – 

The tRNA anticodons that code for the amino acids are as follows.

UGC: cys

CCG: pro

UCG: ser

AUU: ile

What is the correct base of the DNA template that transcribed this enzyme?

• AUU CCG UCG CCG UGC

• UAA GGC AGC GGC ACG

• ATT CCG TCG CCG TGC

• 1. TAA GGC AGC GGC ACG

Multiple Choice

1. All are the following are involved in translation except

• mRNA

• RNA polymerase

• Aminoacyl-tRNA synthetase

• tRNA

Multiple Choice

What is the molecule which acts as an intermediate between the DNA and the ribosomes?

• Messenger RNA

• 1. Transfer RNA

• Ribosomal RNA

• 1. Protein