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1. Introduction of Some Important Enzymes in DNA replication

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1. Introduction of Some Important Enzymes in DNA replication

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DNA Polymerase:

The "builder" of bases

Works in pairs to create 2 identical DNA strands from the original DNA molecule

Creates DNA molecules by assembling nucleotides

Helicase:

Separate double-stranded DNA into single strands so that each strand is allowed to be copied.

Breaks the hydrogen bonds between the nucleotide base pairs in double-stranded DNA using the energy stored in a molecule called ATP, which serves as the energy currency of cells.

Ligase:

"Glues" or seals the fragments of DNA together.

Catalyzes the formation of a phosphodiester bond between nucleotides on one strand of a double stranded DNA molecule.

Creates a covalent linkage between the 5’ phosphate group of one chain with the adjacent 3’ -OH group of another to join nucleotides during DNA replication and also to repair DNA damage.

Primase:

Catalyzes the synthesis of short RNA molecules used as primers, that are complementary to a single-stranded piece of DNA, which serves as its template for DNA polymerases.

"Shows" the way to DNA polymerase.

Exonuclease:

"Proofreads" during DNA polymerisation in DNA replication.

Removes all RNA primers, which are made by primase from the original strands.

Another exonuclease checks, removes, and replaces any errors in the newly formed DNA.

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Each daughter cell need to receive an identical copy of the DNA in cell division.

This can be done by DNA replication.

DNA replication occurs during the synthesis phase or S phase of the cell cycle, before the cell enters mitosis or meiosis.

DNA replication occurs in the nucleus of the eukaryotic cell.

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Before DNA can be replicated, it must first be "unzipped" into two single strands.

There are 4 bases which form pairs between the two strands of DNA, they are Adenine (A), thymine (T), cytosine (C) and guanine (G). Adenine only binds to thymine, while cytosine only binds to guanine.

These interactions between base pairs must be broken by DNA helicase in order for DNA to unwind.

To separate the strands into a Y shape known as the replication fork, DNA helicase disrupts the hydrogen bonding between base pairs. This area is the starting point for replication.

Both strands of DNA are directional, as indicated by 5' and 3' ends. This notation indicates which side group is connected to the DNA backbone.

A a hydroxyl (OH) group is attached to the 3' end, while phosphate (P) group is attached to the 5' end. This directionality is important for replication because it only moves from 5' to 3'.

However, the replication fork is bi-directional; one strand is oriented 3' to 5' (leading strand), while the other is oriented 5' to 3' (following strand) (lagging strand). To account for the directional difference, the two sides are replicated using two different processes.

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The first strand is the easiest to replicate. After the DNA strands have been separated, a primer, which is a short piece of RNA, binds to the 3' end of the strand. As the starting point for replication, the primer always binds.

The enzyme DNA primase creates primers.

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The new strand is created by enzymes known as DNA polymerases through elongation. In bacteria and human cells, there are five different types of DNA polymerases.

Polymerase III is the main replication enzyme in bacteria such as E. coli, while polymerase I, II, IV, and V are in charge of error checking and repair.

During replication, DNA polymerase III binds to the strand at the primer site and begins adding new base pairs complementary to the strand. Polymerases alpha, delta, and epsilon are the primary polymerases involved in DNA replication in eukaryotic cells. Because replication on the leading strand proceeds in the 5' to 3' direction, the newly formed strand is continuous.

The lagging strand initiates replication by binding to several primers. Each primer is only a couple of bases apart. The Okazaki fragments are then added to the strand between the primers by DNA polymerase. Because the newly created fragments are disjointed, the replication process is discontinuous.

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After forming both the continuous and discontinuous strands, an enzyme called exonuclease removes all RNA primers from the original strands. After that, the primers are replaced with the appropriate bases.

Another exonuclease checks, removes, and replaces any errors in the newly formed DNA.

Another enzyme known as DNA ligase connects Okazaki fragments to form a single unified strand. Because DNA polymerase can only add nucleotides in the 5′ to 3′ direction, the ends of the linear DNA present a problem. The ends of the parent strands are made up of repeated DNA sequences known as telomeres.

Telomeres serve as protective caps at the ends of chromosomes, preventing them from fusing with neighbouring chromosomes. Telomerase is a type of DNA polymerase enzyme that catalyzes the synthesis of telomere sequences at the ends of DNA.

When finished, the parent and complementary DNA strands coil into the familiar double helix shape. Finally, replication generates two DNA molecules, each containing one strand from the parent molecule and one new strand.

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The semiconservative model of DNA replication

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7. Semiconservative model of DNA replication 

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7. Semiconservative model of DNA replication 

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During DNA replication:

1. The strands that make up the double helix will serve as templates from which new strands are copied.

2. The new strand is complementary to the “old” or parental strand.

3. Every new double strand has 1 parental strand and 1 new daughter strand. This is known as semiconservative replication.

4.  The 2 DNA copies formed have an identical sequence of nucleotide bases and are divided equally into two daughter cells.

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Quiz

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Wordwall - Create better lessons quicker

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1) What does DNA replication produce? a) one identical copy of DNA b) one nonidentical copy of DNA c) two identical copies of DNA d) two nonidentical copies of DNA 2) Which of the following is the conservative model for DNA replication? a) b) 3) What does the conservative model for DNA replication produce? a) One DNA molecule with 2 new DNA strands and one DNA molecule with 2 original DNA strands b) Two DNA molecules each with one strand of new DNA and one strand original DNA c) One DNA molecule with one strand of new DNA and one strand original DNA and another DNA molecule with two new DNA strands 4) Which of the following is the semi-conservative model for DNA replication? a) b) 5) What does the semi-conservative model for DNA replication produce? a) one DNA molecule with 2 new DNA strands and one DNA molecule with 2 original DNA strands b) two DNA molecules each with one strand of new DNA and one strand of original DNA c) one DNA molecule with one strand of new DNA and one strand original DNA and another DNA molecule with two new DNA strands

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1) What does DNA replication produce? a) one identical copy of DNA b) one nonidentical copy of DNA c) two identical copies of DNA d) two nonidentical copies of DNA 2) Which of the following is the conservative model for DNA replication? a) b) 3) What does the conservative model for DNA replication produce?

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9. Watch DNA Replication in 3D ! ৻(  •̀ ᗜ •́  ৻)

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9. Watch DNA Replication in 3D ! ৻(  •̀ ᗜ •́  ৻)

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10.  Models of DNA Replication | Semi-conservative model |Conservative Model | Dispersive Model

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10.  Models of DNA Replication | Semi-conservative model |Conservative Model | Dispersive Model

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Models of DNA Replication | Semi-conservative model |Conservative Model | Dispersive Model

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11. You may also want to watch some extra info from this video.

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11. You may also want to watch some extra info from this video.

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This channel contains a lot of interesting videos about Biology.
Check it out !

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