• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

The structure of nucleic acid chains (or DNA).

Extracts from this document...


W.Feltham THE STRUCTURE OF NUCLEIC ACID CHAINS (or DNA). Nucleotides are joined together in DNA and RNA by phosphate ester bonds between the phosphate component of one nucleotide and the sugar component of the next nucleotide. An ester bond is a bond which occurs between a Carbon atom and an Oxygen atom. More and more nucleotides can be added on by the same process of forming ester bonds until an immense chain is formed. But no matter how long a polynucleotide chain is, one end of the nucleic acid molecule always has a free -OH group on the sugar at the Carbon known as C3' (called the 3' end) and the other end of the molecule always has a phosphoric acid group at C5' (the 5' end). The Carbons get this name from a counting system illustrated in the next diagram. (Fig 1) Beginning from the "right-hand" side of the sugar, count the Carbons....1', 2', 3' (where the phosphate group of the next nucleotide in a series can be linked via a chemical bond), 4', 5' (where the phosphate group of the previous nucleotide is linked via a chemical bond). ...read more.


The DNA polymerase (once it has reached its starting point as indicated by the primer) then adds nucleotides one by one in an exactly complementary manner, A to T and G to C. DNA polymerase is described as being "template dependent" in that it will "read" the sequence of bases on the template strand and then "synthesize" the complementary strand. The template strand is ALWAYS read in the 3' to 5' direction (that is, starting from the 3' end of the template and reading the nucleotides in order toward the 5' end of the template). The new DNA strand (since it is complementary) MUST BE SYNTHESIZED in the 5' to 3' direction (remember that both strands of a DNA molecule are described as being antiparallel). DNA polymerase catalyses the formation of the hydrogen bonds between each arriving nucleotide and the nucleotides on the template strand. In addition to catalysing the formation of Hydrogen bonds between complementary bases on the template and newly synthesized strands, DNA polymerase also catalyses the reaction between the 5' phosphate on an incoming nucleotide and the free 3' OH on the growing polynucleotide (what we know is called a phosphodiester bond!). ...read more.


This process is shown schematically below. Crick described the DNA replication process and the fitting together of two DNA strands as being like a hand in a glove. The hand and glove separate, a new hand forms inside the old glove, and a new glove forms around the old hand. As a result, two identical copies now exist. The process of DNA replication in all organisms is amazing, but in humans it seems particularly difficult to conceive. The sum of all genes in a human cell-the human genome-is estimated to be approximately 3 billion base pairs, and a single DNA chain might contain up to 250 million pairs of bases. What's even more incredible is how few mistakes are made in this process despite the immense size of human DNA! An error occurs only about once in each 10-100 billion bases. As you would probably expect, the complete process of DNA replication in human cells takes several hours. To replicate such huge molecules as human DNA at this speed requires not one, but many replication forks, forming replication bubbles and producing many segments of DNA strands that eventually meet up together and are joined to form the newly synthesized double helix. ...read more.

The above preview is unformatted text

This student written piece of work is one of many that can be found in our GCSE Variation and Inheritance section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Here's what a star student thought of this essay

4 star(s)

Response to the question

This essay outlines the structure of DNA chains to a strong level for GCSE, even adding information about replication. I would've like to have seen an exploration of the structure of singular DNA nucleotides. Diagrams are used well to support ...

Read full review

Response to the question

This essay outlines the structure of DNA chains to a strong level for GCSE, even adding information about replication. I would've like to have seen an exploration of the structure of singular DNA nucleotides. Diagrams are used well to support the scientific explanations of replication, but there are plenty more that could've been included to directly answer the question.

Level of analysis

The explanation of DNA strands is strong, using higher level concepts such as 3' and 5' ends. Just to note, I would always refer to them as 3-prime and 5-prime in an exam, just to prevent and ambiguity. I liked how they referred to the ester bonds in a DNA nucleotide, however their understanding could be proven if they'd included a diagram which had labelled this bond. Similarly, I would've liked to have a seen a discussion of the deoxyribose sugar base and the phosphate group. Including concepts such as this will ensure higher marks are within reach. When discussing DNA strands, I think it's key to show a diagram of the orientation of DNA nucleotides. This naturally leads onto discussion of complementary base pairing, which isn't discussed in the structure section. Yes, it is mentioned during replication, however I think this is something which needs to be addressed early on. Although discussing replication is not relevant to the task, plenty of higher level concepts are used. I particularly liked the discussion of DNA polymerase to separate the strands - a concept explored at A-Level.

Quality of writing

This essay is written well, however it is slightly worrying that the essay spends more time discussing replication than structure, which is the task set. Spelling, punctuation and grammar are used well and scientific terms are used correctly when appropriate.

Did you find this review helpful? Join our team of reviewers and help other students learn

Reviewed by groat 17/02/2012

Read less
Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related GCSE Variation and Inheritance essays

  1. Marked by a teacher

    Protein Synthesis is the process whereby DNA (deoxyribonucleic acid) codes for the production of ...

    3 star(s)

    It provides a base triplet, a sequence of three bases on one of the strands of DNA, that code for one amino acid. The sequence of base triplets on DNA molecules determines the order of the amino acids on the protein chain.

  2. Marked by a teacher

    Cloning. Should it be banned? I will explain all the different types of cloning ...

    * Moreover, cloning will put human and animal rights at stake. Will cloning fit into our ethical and moral principles? Cloning will leave man just another man-made being. Won't it devalue mankind? Won't it undermine the value of human life?

  1. Peer reviewed

    Natural variation

    3 star(s)

    The children ranged from 15-23cm in foot size. * After I measured their foot I measured the height of the children. I made sure they stood straight against a wall with their heels touching the wall. * When parents came to pick their child up, I asked them to come into the office where I was doing my investigation.

  2. There are a number of treatments available to infertile couples. They are called: Artificial ...

    The Roman Catholics have this approach because none of the treatments have any sex act. They say that God's plan for reproduction demands sex to be a portion of it. Also IVF compromise throwing away the unwanted eggs or using them for investigation which is no different from abortion.

  1. Stem Cell Research

    Two other cell types are significant to an appropriately functioning heart are the vascular endothelial cell (this forms the inner lining of new blood vessels) and the smooth muscle cell (this forms the wall of blood vessels)6. Obviously, the heart has a very large demand for blood flow, and these

  2. The causes and consequences of variation

    A person who only shows the sickle cell trait (is heterozygous for the disease) benefits from the mutation if they are living in an area where malaria is a problem, as it makes them immune to the malaria parasite. However, those with the disease generally suffer from pain in joints, kidney damage and eventually death.

  1. Human cloning is most notably one of the most controversial issues in medical science.

    Dolly was proof that the possibility of performing gene transfer using adult cells can result in a cloned adult mammal. Wilmut and his colleagues implanted 30 developed embryos into Blackface ewes, and one of these pregnancies resulted in the birth of a Fin Dorset lamb, which was Dolly.

  2. Cloning Human Beings Is Not Ethical.

    If the Raelian cult's claim is false, it is just a matter of time before it actually happens. Not only are the Raelians engaged in this disturbing enterprise, but also a fertility clinic in Italy and an embryology laboratory in Kentucky also claim to be close (Limbaugh, 2003).

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work