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Macromolecules

Macromolecules are a class of large molecules that are very important biologically. These molecules are involved in all of the structures and processes of cells and organisms.

The four different types of macromolecules:

Proteins

Lipids

Carbohydrates

Nucleic acids

Each type performs specific functions in the cell.

All macromolecules are polymers (monomer units joined to form polymers). They are built and broken down in the same way, by adding or subtracting monomers through condensation and hydrolysis reactions.

For examples; all proteins are made of the same twenty amino acids, and all nucleic acids are made of the same five nucleotides.

Nucleic AcidsNucleic acids are polymers of nucleotides, they are

responsible for storing and transmitting the hereditary information of cells and organisms.

Nucleotides are carbon ring structures containing nitrogen linked to a 5-carbon sugar.

5-carbon sugar is either a ribose or a deoxyribose making the nucleotide either a ribonucleotide or a deoxyribonucleotide.

There are two types of nucleic acids:1. Deoxyribose nucleic acids (DNA)

2. Ribose nucleic acids (RNA):- Messenger RNA (mRNA)- Transfer RNA (tRNA)- Ribosomal RNA (rRNA)

DNA, which is found in the nucleus of eukaryotic cells and the nucleoid of prokaryotic cells, contains the genetic information cells need to make proteins.

RNA is found throughout cells, and is required to translate the information of DNA into the actual amino acid sequences of proteins.

Proteins, including structural proteins, enzymes and others, are absolutely essential to life.

Both DNA and RNA are polymers composed of repeating subunits, or monomers, called nucleotides.

The genetic information that is stored in molecules of DNA or RNA is based on the sequence of these nucleotides.

Each nucleotide is composed of three parts: - Phosphate group- Five carbon sugar (ribose or deoxyribose)- Nitrogenous base.

In nucleic acids, nucleotides are linked together through condensation reactions, between the phosphate groups and sugars of adjacent nucleotides. These covalent bonds are called phosphodiester linkages.

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Nucleotides

Nucleic acids consist of nucleotides that have a sugar, nitrogen base, and phosphate

nucleoside   

Sugar

Base

PO4

Ribose is a pentose

C1

C5

C4

C3

C2

O

RIBOSE DEOXYRIBOSE

CH2

OH

H

OH

C

C

OH

OH

C

O

H HH

C

CH2

OH

H

OH

C

C

OH

H

C

O

H HH

C

Spot the difference

Nitrogenous Bases

There are five different nitrogenous bases found in nucleic acids; Cytosine (C), Thymine (T), Uracil (U), Adenine (A), and Guanine (G).

Cytosine, thymine and uracil are classified as pyrimidines, while Adenine and guanine are classified as purines.

A (adenine) always bonds with T (thymine) or U (uracil), and C (cytosine) always bonds with G (guanine).

Primary Structure of Nucleic Acids

• The primary structure of a nucleic acid is the nucleotide sequence.• The nucleotides in nucleic acids are joined by phosphodiester

bonds.• The 3’-OH group of the sugar in one nucleotide forms an ester

bond to the phosphate group on the 5’-carbon of the sugar of the next nucleotide.

The sugar-phosphate backbone

• The nucleotides are all orientated in the same direction.

• The phosphate group joins the 3rd carbon of one sugar to the 5th carbon of the next in line.

P

P

P

P

P

P

© 2007 Paul Billiet ODWS

Adding in the bases

• The bases are attached to the 1st Carbon.

• Their order is important It determines the genetic information of the molecule.

P

P

P

P

P

P

G

C

C

A

T

T

© 2007 Paul Billiet ODWS

Reading Primary Structure

• A nucleic acid polymer has a

free 5’-phosphate group at one

end and a free 3’-OH group at

the other end.

• The sequence is read from the

free 5’-end using the letters of

the bases.

• This example reads

5’—A—C—G—T—3’

• Each strand of the double helix is oriented in the opposite direction

5- end 3- end

3- end 5- end

P

P

P

PP

P

P

P

DNA vs RNA

• RNA is much more abundant than DNA.

• Differences between RNA and DNA:-DNA and RNA have slightly different roles for cells; DNA stores the genetic information of cells, and RNA translates this information into the amino acid sequences of proteins.- The pentose sugar in RNA is ribose, in DNA it’s deoxyribose.

- In RNA, uracil replaces the base thymine (U pairs with A).- RNA is single stranded while DNA is double stranded- RNA molecules are much smaller than DNA molecules.

• There are three main types of RNA:

Ribosomal (rRNA), messenger (mRNA) and transfer (tRNA).

Protein Synthesis

• The two main processes involved in protein synthesis:- the formation of mRNA from DNA (transcription)- the conversion by tRNA to protein at the ribosome (translation)

• Transcription takes place in the nucleus, while translation takes place in the cytoplasm.

• Genetic information is transcribed to form mRNA much the same way it is replicated during cell division.

• The flow of genetic information

DNA RNA Protein.– Protein synthesis occurs

in the ribosomes.– In eukaryotes, DNA is

located in the nucleus, but most ribosomes are in the cytoplasm.

– mRNA is used to send a message from the DNA to the ribosome.

– Prokaryotic cells do not have nuclei, but still use RNA to send a message from the DNA to the ribosomes to translate the coded information into amino acid.

• Nucleotides, or derivatives of them, play many important roles for cells:

- ATP, the universal ‘energy currency’ of cells, is a modified molecule of adenine that carries three phosphate groups.

- Also, the cofactors NAD and NADP, are important in many biochemical reactions.

DNA and Organism Evolution• In addition to producing proteins, nucleic acids, particularly DNA, have great evolutionary significance. • DNA is copied and passed from cell to cell and from parent to offspring.• Comparing the DNA of different organisms can give us an informative look into their evolutionary history. • Organisms inherit DNA from their parents.

– Each DNA molecule is very long and usually consists of hundreds to thousands of genes.

– Contains coded information that programs all cell activities.– When a cell reproduces itself by dividing, its DNA is

copied and passed to the next generation of cells.