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Rna World and The Origins Of Life

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Learninsta presents the core concepts of Biology with high-quality research papers and topical review articles.

Rna World and The Origins Of Life

A typical cell contains about ten times as much RNA as DNA. The high RNA content is mainly due to the variety of roles played by RNA in the cell. Fraenkel-Conrat and Singer (1957) first demonstrated that RNA is the genetic material in RNA containing viruses like TMV (Tobacco Mosaic Virus) and they separated RNA from the protein of TMV viruses.

Three molecular biologists in the early 1980’s (Leslie Orgel, Francis Brick and Carl Woese) independently proposed the ‘RNA world’ as the first stage in the evolution of life, a stage when RNA catalysed all molecules necessary for survival and replication. The term ‘RNA world’ first used by Walter Gilbert in 1986, hypothesizes RNA as the first genetic material on earth.

There is now enough evidence to suggest that essential life processes (such as metabolism, translation, splicing etc.,) evolved around RNA. RNA has the ability to act as both genetic material and catalyst. There are several biochemical reactions in living systems that are catalysed by RNA. This catalytic RNA is known as ribozyme. But, RNA being a catalyst was reactive and hence unstable.

This led to evolution of a more stable form of DNA, with certain chemical modifications. Since DNA is a double stranded molecule having complementary strand, it has resisted changes by evolving a process of repair. Some RNA molecules function as gene regulators by binding to DNA and affect gene expression. Some viruses use RNA as the genetic material.

Andrew Fire and Craig Mellow (recipients of Nobel Prize in 2006) were of the opinion that RNA is an active ingredient in the chemistry of life. The types of RNA and their role have been discussed in class XI.

Chemistry Of Nucleic Acids

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Chemistry Of Nucleic Acids

Having identified the genetic material as the nucleic acid DNA (or RNA), we proceed to examine the chemical structure of these molecules. Generally nucleic acids are a long chain or polymer of repeating subunits called nucleotides. Each nucleotide subunit is composed of three parts: a nitrogenous base, a five carbon sugar (pentose) and a phosphate group.

Pentose sugar

There are two types of nucleic acids depending on the type of pentose sugar. Those containing deoxyribose sugar are called Deoxyribo Nucleic Acid (DNA) and those with ribose sugar are known as Ribonucleic Acid (RNA). DNA is found in the nucleus of eukaryotes and nucleoid of prokaryotes. The only difference between these two sugars is that there is one oxygen atom less in deoxyribose.

Nitrogenous bases

The bases are nitrogen containing molecules having the chemical properties of a base (a substance that accepts H+ ion or proton in solution). DNA and RNA both have four bases (two purines and two pyrimidines) in their nucleotide chain. Two of the bases, Adenine (A) and Guanine (G) have double carbon – nitrogen ring structures and are called purines. The bases, Thymine (T), Cytosine (C) and Uracil (U) have single ring structure and these are called pyrimidines. Thymine is unique for DNA, while Uracil is unique for RNA.

The phosphate functional group

It is derived from phosphoric acid (H3PO4), has three active OH– groups of which two are involved in strand formation. The phosphate functional group (PO4) gives DNA and RNA the property of an acid (a substance
that releases an H+ ion or proton in solution) at physiological pH, hence the name nucleic acid.

The bonds that are formed from phosphates are esters. The oxygen atom of the phosphate group is negatively charged after the formation of the phosphodiester bonds. This negatively charged phosphate ensures the retention of nucleic acid within the cell or nuclear membrane.

Nucleoside and nucleotide

The nitrogenous base is chemically linked to one molecule of sugar (at the 1-carbon of the sugar) forming a nucleoside. When a phosphate group is attached to the 5′ carbon of the same sugar, the nucleoside becomes a nucleotide. The nucleotides are joined (polymerized) by condensation reaction to form a polynucleotide chain.

The hydroxyl group on the 3′ carbon of a sugar of one nucleotide forms an ester with the phosphate of another nucleotide. The chemical bonds that link the sugar components of adjacent nucleotides are called phosphodiester bond (5′ → 3′), indicating the polarity of the strand.

The ends of the DNA or RNA are distinct. The two ends are designated by the symbols 5′ and 3′. The symbol 5′ refers to carbon in the sugar to which a phosphate (PO4) functional group is attached. The symbol 3′ refers to carbon in the sugar to which hydroxyl (OH) functional group is attached. In RNA, every nucleotide residue has an additional –OH group at 2′ position in the ribose. Understanding the 5′ → 3′ direction of a nucleic acid is critical for understanding the aspects of replication and transcription.

Based on the X – ray diffraction analysis of Maurice Wilkins and Rosalind Franklin, the double helix model for DNA was proposed by James Watson and Francis Crick in 1953. The highlight was the base pairing between the two strands of the polynucleotide chain. This proposition was based on the observations of Erwin Chargaff that Adenine pairs with Thymine (A = T) with two hydrogen bonds and Guanine pairs with Cytosine (G ≡ C) with three hydrogen bonds.

The ratios between Adenine with Thymine and Guanine with Cytosine are constant and equal. The base pairing confers a unique property to the polynucleotide chain. They are said to be complementary to each other, that is, if the sequence of bases in one strand (template) is known, then the sequence in the other strand can be predicted. The salient features of DNA structure has already been dealt in class XI.

DNA Is The Genetic Material

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DNA Is The Genetic Material

Many biologists despite the earlier experiments of Griffith, Avery and others, still believed that protein, not DNA, was the hereditary material in a cell. As eukaryotic chromosomes consist of roughly equal amounts of protein and DNA, it was said that only a protein had sufficient chemical diversity and complexity to encode the information required for genetic material. In 1952, however, the results of the Hershey-Chase experiment finally provided convincing evidence that DNA is the genetic material.

Hershey and Chase experiment on T2 bacteriophage

Alfred Hershey and Martha Chase (1952) conducted experiments on bacteriophages that infect bacteria. Phage T2 is a virus that infects the bacterium Escherichia coli. When phages (virus) are added to bacteria, they adsorb to the outer surface, some material enters the bacterium, and then later each bacterium lyses to release a large number of progeny phage.

Hershey and Chase wanted to observe whether it was DNA or protein that entered the bacteria. All nucleic acids contain phosphorus, and proteins contain sulphur (in the amino acid cysteine and methionine). Hershey and Chase designed an experiment using radioactive isotopes of Sulphur (35S) and phosphorus (32P) to keep separate track of the viral protein and nucleic acids during the infection process.

The phages were allowed to infect bacteria in culture medium which containing the radioactive isotopes 35S or 32P. The bacteriophage that grew in the presence of 35S had labelled proteins and bacteriophages grown in the presence of 32P had labelled DNA.

The differential labelling thus enabled them to identify DNA and proteins of the phage. Hershey and Chalse mixed the labelled phages with unlabeled E coli and allowed bacteriophages to attack and inject their genetic material. Soon after infection (before lysis of bacteria), the bacterial cells were gently agitated in a blender to loosen the adhering phase particles.

It was observed that only 32P was found associated with bacterial cells and 32S was in the surrounding medium and not in the bacterial cells. When phage progeny was studied for radioactivity, it was found that it carried only 32P and not 35S (Fig. 5.2). These results clearly indicate that only DNA and not protein coat entered the bacterial cells. Hershey and Chase thus conclusively proved that it was DNA, not protein, which carries the hereditary information from virus to bacteria.

In Search Of The Genetic Material

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Learninsta presents the core concepts of Biology with high-quality research papers and topical review articles.

In Search Of The Genetic Material

As early as 1848, Wilhelm Hofmeister, a German botanist, had observed that cell nuclei organize themselves into small, rod like bodies during mitosis called chromosomes. In 1869, Friedrich Miescher, a Swiss physician, isolated a substance from the cell nuclei and called it as nuclein. It was renamed as nucleic acid by Altman (1889), and is now known as DNA. By 1920, it became clear that chromosomes are made up of proteins and DNA.

Many experiments were carried out to study the actual carriers of genetic information. Griffith’s experiment proved that DNA is the genetic material which has been dealt in class XI. Bacterial transformation experiments provided the first proof that DNA is the genetic material. However, he could not understand the cause of bacterial transformation, and the biochemical nature of genetic material was not defined from his experiments.

Later, Oswald Avery, Colin Macleod and Maclyn McCarty in 1944 repeated Griffith’s experiments in an ‘in vitro’ system in order to identify the nature of the transforming substance responsible for converting a nonvirulent strain into virulent strain. They observed that the DNA, RNA and proteins isolated from the heat-killed S-strain when added to R-strain changed their surface character from rough to smooth and also made them pathogenic (Fig. 5.1).

But when the extract was treated with DNase (an enzyme which destroys DNA) the transforming ability was lost. RNase (an enzyme which destroys RNA) and proteases (an enzyme which destroys protein) did not affect the transformation.

Digestion with DNase inhibited transformation suggesting that the DNA caused the transformation. These experiments suggested that DNA and not proteins is the genetic material. The phenomenon, by which DNA isolated from one type of cell (S – strain), when introduced into another type (R – strain), is able to retain some of the properties of the S – strain is referred to as transformation.
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Applications of Computers in Accounting Class 11 Notes Accountancy Chapter 12

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By going through these CBSE Class 11 Accountancy Notes Chapter 12 Applications of Computers in Accounting, students can recall all the concepts quickly.

Applications of Computers in Accounting Notes Class 11 Accountancy Chapter 12

Computers are becoming indispensable in our day-to-day life. It has brought a complete revolution in every sphere of human activity. It becomes an essential tool of today’s society.

Examples of their increasing uses are; reservation in railway and air tickets, to forecast weather, preparing customer’s bill, diagnosing diseases, recording the monetary transaction of customers in the bank, etc. In fact, computers have become indispensable in almost every field of communication, commerce, industry, science and research, technology, transport.

Computers are not used only by engineers, scientists, and mathematicians but even in the typesetting for printing, TV programming, film editing, music composing, etc.

Both in the commercial and personal areas, there are so many works which we are not able to do. due to lack of time. The computer makes it possible by doing our work speedily and efficiently. Computers are nowadays being used on a large scale in business houses for a number of functions. They are used for recording and posting transactions, maintaining journals, ledgers, stock records, pay-rolls, wages records, purchases and sales records, etc. The computer performs all the accounting operations at a phenomenal speed and with a high degree of accuracy.

Limitations of a Computer System:

  1. Lack of common sense.
  2. Lack of feelings.
  3. Lack of IQ (Intelligence Quotient).
  4. Lack of decision-making.
  5. Complex and rigid procedure.
  6. Installation cost.
  7. Frequent changes.
  8. Costly maintenance.
  9. Unemployment.
  10. Loss of data: Backup required.

Difference between Human and Computer:
Following are the differences between Human and Computer:

  1. Memory: Human memory is limited however computer’s memory has no limits.
  2. Speed: is faster than human.
  3. Repetitive task: can be performed by computers errorlessly.
  4. Computers do not possess mind and work as directed by a human. It has no impact of emotions however human is emotional and decides on its own, which computers cannot.

Difference between Hardware and Software:
Applications of Computers in Accounting Class 11 Notes Accountancy 1
Difference between Computer and Calculator
Applications of Computers in Accounting Class 11 Notes Accountancy 2
Components of Computer:
The computer is an electronic device that stores and processes information to give meaningful results. It takes information from an input device and after processing the information, gives the processed information to an output device.
Applications of Computers in Accounting Class 11 Notes Accountancy 3
Three basic components of a computer are:

  1. Input Device
  2. Central Processing Unit (CPU)
  3. Output Device.

Applications of Computers in Accounting Class 11 Notes Accountancy 4
Applications of Computers in Accounting Class 11 Notes Accountancy 5
Need of Computer in Accounting or Evolution of Computerised Accounting:
In past, the business transactions were limited so that they were handled manually. Trader himself or by taking the service of Accountant to maintain the books of accounts such as cashbook, journal, and ledger. As the economy starts growing, the trades also developed and the number of transactions starts increasing.

With the help of scientific development, new machines were invented which perform the large work in a short time, for e.g. billing the machine. With the substantial increase in the number of transactions, the technology advanced further. The success of a growing organization with the complexity of transactions tended to depend on resource optimization, quick decision-making, and control. Such a system of maintaining accounting records becomes convenient with the computerized accounting system.

Computers are required in accounting for the following tasks:

  1. To note down business transactions.
  2. Processing and maintaining payrolls.
  3. Maintaining personal records.
  4. Keeping effective stock control.
  5. Invoicing of sales.
  6. To maintain ledgers of creditors.
  7. To make bills.
  8. To prepare accounts of credit and debit.
  9. Classification of accounting transactions through sorting; merging and updating.
  10. Prepare reports in the form of ledger accounts and balance sheets.
  11. Stores accounting.

Automation of Accounting Process:
An organization is a col section of interdependent decision-making units that works for the achievement of common goals. Every organization, as a system, performs the same function that accepts inputs and transforms them into outputs. Information system facilitates the decision-making regarding allocation of resources.

The information thus becomes the most important resource in business. With the increasing use of information systems in organizations. Transaction Processing Systems (TPS) have started playing important role in supporting business operations. A large number of devices are now available to automate the input process for TPS.

Transaction Processing System:
They can perform and records the daily routine transactions which are necessary to conduct the business.

Process of TPS

  1. Collection of data.
  2. Validation of data
  3. Manipulation of data
  4. Storage of data
  5. Generation of output
  6. Query support.

Features of Computerised Accounting System:

  1. Online input and storage of accounting data.
  2. Automatically update the ledger etc.
  3. Printout of purchases and sales invoices.
  4. Grouping of accounts.
  5. Instant Reports like Stock Statement, Trial Balance, Trading and Profit, and Loss A/c, Balance Sheet, Value Added Tax (VAT), Payroll, etc.
  6. Codification of accounts and transactions.

Management Information System (MIS) and Accounting Information System (AIS):
Accounting information is one of the most important information used by the management in taking decisions. However, the scope of accounting information is limited. Accounting information when contained in a computerized environment is called an accounting information system.

However, management information system is a much broader term and incorporates many functional information systems like production, marketing, research, and development, etc., besides accounting information systems.

A management information system is an information system that generates, accurate, timely, and organized information to help managers make decisions, control processes, solve problems, supervise activities and track progress.

An accounting information system identifies, collects processes, and communicates the economic information of an organization to a wide variety of users. Every accounting system is a part of an accounting information system where AIS is part of a management information system.

Meaning of Computer:
The dictionary meaning of computer is “an electronic calculating machine”. This meaning of computer does not reflect upon the true capabilities of a computer. A computer is a very versatile machine capable of performing diversified functions at an incredibly fast speed with accuracy.

It converts raw data into meaningful information. The data is fed into the computer and in case of need, it can be retrieved and converted into output.

A computer is an electronic machine that operates on given instruction and PROCESSES the INPUT DATA, to convert it into some OUTPUT.

“A computer is a data processor that can perform substantial computation, including numerous arithmetical and logical operations, without intervention by a human operator during the run.” – International Standards Organisation

‘‘A computer is a device capable of solving problems by accepting data, performing described operations on the data, and supplying the results of these operations. —U.S. Institute

Thus, a computer is an electronic device, in which a lot of information or data can be stored so Jhat the data can be used in the future. It can also perform various calculations at a very high speed.

Elements of Computer System
A Computer System is a combination of six elements:

  1. Hardware
  2. Software
  3. People.
  4. Procedure
  5. Data
  6. Connectivity.

1. Hardware: The hardware of a computer may be classified under the following categories:
Applications of Computers in Accounting Class 11 Notes Accountancy 6
They are further classified as follows:
Input Devices

  1. Keyboard
  2. Mouse
  3. Joystick
  4. Touch Screen
  5. Scanner
  6. Voice Input System
  7. Magnetic Ink Character Reader (MICR)
  8. Bar Code Reader (BCR)

Output Devices:

  1. Monitor or Visual Display Unit (VDU)
  2. Printers
  3. Voice Response System (VRS)

Central Processing Unit (CPU)

  1. Storage Unit
  2. Control Unit
  3. Arithmetic Logic Unit (ALU)

Secondary Storage Devices

  1. Hard Disk
  2. Floppy Disk
  3. Compact Disk
  4. DVD (Digital Visual Disc)

2. Software: A set of programs, which is used to work with hardware is called its software. There are six types of software which are following:

  1. Operating System
  2. Utility Software
  3. Application Software
  4. Language Processors
  5. System Software
  6. Connectivity Software.

3. People: People are basically those individuals who use computers to develop, maintain and use the information system. They are also called live-ware of the computer. The main categories of people involved with the computer system are:

  1. System Analysts
  2. Computer Operators
  3. Programmers.

4. Procedures: The procedures are the various operations performed in a certain way in order to achieve some desired results.

There are basically three types of procedures:

  1. Software-oriented
  2. Hardware-oriented
  3. Internal procedure.

5. Data: The data is therefore processed and organized to create information that is relevant and can be used for decision-making.

6. Connectivity: The element of connectivity refers to the way in which a computer system is connected to other electronic devices and link-ups such as satellite links, internet, telephone lines, etc.

Capabilities or Features of a Computer System
1. High Speed: A computer can perform millions of operations in one second. The calculations will be error-free.

2. Automatic IHachine: Once the data are fed into the computer, it executes the instructed functions without human intervention.

3. Accuracy: This machine is extremely accurate. Its operations are error-free and the information derived from that is more reliable.

4. Reliability: Computer can perform jobs of repetitive nature any number of times. They are immune to tiredness, boredom, or fatigue. Therefore, they are more reliable than human beings.

5. Versatility: A computer can perform a wide variety of jobs simple as well as complex.

6. Storage: The storage capacity, of a computer, is so large that it can store any volume of information or data for being processed.

7. Scientific Approach: The computer operates scientifically and never gets emotional while solving problems.

8. Work on Special Language: A computer can perform many functions by giving or programming in any one language of computers, which are developed in order to feed the information and data into a computer.

9. Logical decision: Computer has the capability to make decisions that are based on certain conditions.

10. Use of Binary System: The computer uses a two-way system known as Binary System, not the decimal system.

Applications of Computers in Accounting Class 11 Notes Accountancy 7
Applications of Computers in Accounting Class 11 Notes Accountancy 8
Relationship of Management Information System with other functional Information Systems
Designing of Accounting Reports: When the related information is summarised to meet a particular need it is called a report. It must be effective, efficient, and useful for decision-making.

Every accounting report must be able to fulfill the following features:

  1. Relevance
  2. Accuracy
  3. Completeness
  4. Timeliness
  5. Summarisation.

Types of Reports

  1. Summary Reports
  2. Customer Reports
  3. Supplier Reports
  4. Demand Reports
  5. Exception Reports
  6. Responsibility Reports.

Steps in Designing Reports

  1. Definition of objectives
  2. Structure or format of the report
  3. Querying with database
  4. Finalizing the report.

Data Interface between the Information System:
I. Relationship between Accounting Information System (AIS), Manufacturing Information System and Unman Resource Information System.
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II. Relationship between AIS and Marketing Information System: Marketing and Sales Department perform following activities:

  1. Inquiry Process
  2. Creating Contacts
  3. Order Taking
  4. Dispatching Goods
  5. Billing

The accounting sub-system transaction cycle includes:

  1. Processing of sales order
  2. Credit Authorisation
  3. Keeping custody of goods
  4. Stock Position
  5. Dispatch Details
  6. Accounts Receivable etc.

III. Relationship between AIS and Manufacturing Information
System: Production Department performs the following activities:

  1. Preparing plans, schedules ‘
  2. Issue of material requisition forms
  3. Issue of job cards
  4. Issue of stock
  5. Handling of vendor invoices
  6. Payment to vendors/suppliers

The accounting sub-system transaction cycle includes:

  • Processing purchases order
  • Advance payment
  • Stock Updation
  • Accounts payable etc.

Application of Computer in Accounting
Although computers influence every field of accounting, however, its usage in normal modes is mentioned below:
(a) Recording of Business Transactions
(b) Accounting of Debtors
(c) Stores Accounting
(d) Pay-toll Accounting.

(a) Problems that arise due to manual accounting such as complexity, percentage of error, delayed work can be easily rectified using a computer in accounting. Computers can automatically generate ledger postings of business transactions. Using computers, can therefore completely maintain ledger accounts.

(b) Debtors account can easily be maintained via computers. Computers can generate accurate figures for the debtor’s account. They can also be used to prepare reminders to debtors in order to timely collect debt.

(c) Stores Accounting: In stores accounting, the contribution of computers is appreciable. They can be used for

  1. Daily Stock Position
  2. Price of Stock
  3. Need of goods to be credited.

(d) Payroll Accounting: To generate pay of employees in an organization, wages, salary, bonus, allowances, etc. are calculated. Furthermore, employee provident fund, income tax, etc. is deducted from salary. Traditional manual accounting is difficult and bound to make errors that can be made easy, fast, and accurate through the use of payroll accounting.
Applications of Computers in Accounting Class 11 Notes Accountancy 10
Components Of Computerised Accounting Software System