CH 12 Bio

DNA helicase

(Scissors) Breaks H bond between DNA strands

There are only three components to a nucleotide

*A sugar (called deoxyribose) * A Phosphate (1 phosphorus atom joined to 4 oxygen atoms) *One of 4 bases (Adenine, Guanine, Cytosine, Thymine)

Explain DNA complementary base pairing and its rules

*A with T: the purine adenine (A) always pairs with. the pyrimidine thymine (T) *C with G: the pyrimidine cytosine (C) always pairs with. the purine guanine (G)

Lagging strand

A discontinuously synthesized DNA strand that elongates by means of Okazaki fragments, each synthesized in a 5' to 3' direction away from the replication fork.

What part of the DNA nucleotides hold your genetic information

BASES A-T G-C

The importance of complementary base pairing o

Complementary base pairing is very important in the conservation of the base sequence of DNA. This is because adenine always pairs up with thymine and guanine always pairs up with cytosine. As DNA replication is semi-conservative (one old strand an d one new strand make up the new DNA molecules), this complementary base pairing allows the two DNA molecules to be identical to each other as they have the same base sequence. The new strands formed are complementary to their template strands but also identical to the other template. Therefore, complementary base pairing has a big role in the conservation of the base sequence of DNA.

Explain the roles of DNA ligase, primer, primase, helicase, and topoisomerase.

DNA ligase joins pieces of DNA together, mainly joins Okazaki fragments with the main DNA piece. Primer is what starts the reading, primase is the enzyme that allows the primer to attach, helicase is what unzips the double stranded DNA, toposiomerases help release the tension that builds by the winding and unwinding of the strands. and finally the single strand binding proteins bind to the single strands of DNA when they are single, they support it and dont allow it to wind again (which is a more stable conformation of DNA mainly because of hydrogen bonding between the bases and such). all can be used for dna replication, and some also for transcription.

Identify the ways in which DNA can be repaired

DNA polymerase-reads and copies ,it will recoginze mistakes and fix it. DNA Liagase If repairs fail then mutation can occur

Explain how the directionality of the strands of the double helix influence the process of DNA replication

DNA polymerases only work in the 3' to 5' direction so on one of the DNA strands this is easy as it opens up in that direction. But on the other strand (the lagging strand) the enzyme must work in the opposite direction, meaning it can only build discontinuous fragments as the double helix unwinds

Basic structural characteristics of DNA

Double stranded helix Anti parallel Strands connected together by Hbonds Made of nucleotides, base A-T,G-C

Distinguish between the leading strand and the lagging strand

During DNA replication, the two antiparallel DNA strands are split in to the 'leading' and the 'lagging' strand by the enzyme DNA Helicase. ... However, the lagging strand runs in the opposite direction, from 3prime to 5prime. This means nucleotides can only be added discontinuously.

Types of bond that hold nucleotides together as well as type of bond that hold the two strands of the double helix together

Hbonds aka Hydrogen bonds

DNA ligase

Joins DNA segments on discontinuous strand,closes gaps of little pieces.

Role of DNA polymerase

Reads the sequence A-T,G-C Links complementary nucleotides into new strand Can ONLY READ 5' to 3' direction therefore only adds nucleotide to 3' end of a strand

Describe the process of DNA replication step 1

Step 1: The Separation of DNA Strands Topoisomerase untwists the double helix. The steps of DNA replication always begin by separating a twisted strand into two untwisted molecular strands. It happens in the specific area of a chromosome known as the "origins". The origins contain a series of codes that attract the helicase, a protein that aids in the separation of the strands. Once the helicase locates the origins, it sends out signals inside the cell for other replication initiator proteins to help out in the separation. DNA strands are being separated by breaking the hydrogen bonds between the nucleotide base pairs, such as those of adenine (A) and thymine (T), and guanine (G) and cytosine (C). *Topisomoerase and Helicase unwind and separate double helix.

Describe the process of DNA replication Step 2

Step 2: Replication Fork Formation Splitting the original double helix into two strands visually presents a Y-shaped formation known as the replication fork. Each prong appears as an elongated line that requires an identical half to match in order to form a new pair of strands. One of the separated strands is called the leading strand, which is constantly utilized for DNA synthesis while the lagging strand is responsible for the complimentary strand's synthesis. *Primer attach to parent strand

Describe the process of DNA replication Step 3

Step 3: Binding of Bases to Each Strand Both leading strand and lagging strand already has base patterns from the start and it serves as the template for the corresponding strands. For each strand, the bases match with the free floating nucleotides present inside the cell following the nucleotide base pairing rules to establish the hydrogen bonding between a separated strand and a new matching strand. It is made possible by the DNA polymerase, an enzyme that functions like a sewing machine in matching and zipping both strands together. The replication process does not result to a brand new chain of DNA. It is always a mixture of both the original strand that is conserved as a partner all throughout the continuous steps of DNA replication process and the recently made strand. This process is recognized as the semiconservative replication. *Starting at primer DNA polymerase attaches nucleotides using base pairing rules

Describe the process of DNA replication Step 4

Step 4: The Termination of the Replication Process The termination process occurs as soon as the DNA polymerase enzyme arrived at the edge of the strands where no more possible replication could occur. But before the process is completed, it goes through the process of repair to correct errors such as mismatching of nucleotides. After this step, the DNA replication is completed. *Strands wind back together

Explain how the lagging strand is synthesized even though DNA polymerase can add nucleotides only to the 3' end.

The lagging strand is synthesized in a series of short fragments called okazaki fragments. Each okazaki fragment is bonded covalently by DNA ligase to the others to create a continuous strand. Each fragment requires a primer. These small fragments are generated by the polymerase making a small 5' to 3' fragment inside the replication bubble as it opens. Then all the little fragments are joined together

What units are put together to make a DNA molecule

The two DNA strands are also known as polynucleotides since they are composed of simpler monomeric units called nucleotides. Each nucleotide is composed of one of four nitrogen-containing nucleobases (cytosine [C], guanine [G], adenine [A] or thymine [T]), a sugar called deoxyribose, and a phosphate group.

Define "antiparallel" and explain why continuous synthesis of both DNA strands is not possible.

The two strands of DNA run in different directions. One is 5' to 3', the other is the reverse. DNA replication can only occur from 5' to 3'. So the strand running 3' to 5' must be done in pieces running from 5 to 3 in fragments called Okazaki fragments.

Topoismoerase

Untwists the double helix./uncoil DNA

leading strand

When replication begins, the two parent DNA strands are separated. One of these is called the leading strand, and it is replicated continuously in the 3' to 5' direction

A DNA nucleotide consists of three parts

a nitrogen base, a five-carbon sugar called deoxyribose, and a phosphate group. There are four different DNA nucleotides, each with one of the four nitrogen bases (adenine, thymine, cytosine, and guanine). ... The thymine nucleotide does not occur in RNA. It is replaced by uracil