DNA Traits

 
 
   

Objectives for today:
*Undersand DNA configuration.

*Know the stages in cell reproduction.

*Understand the configuration of a chromosome.

* Identify differences between DNA and RNA.
                       
     

DNA is a complex molecule (polymer) found in all living things.

The primary function of DNA is to store and transmit genetic information that tells cells which proteins to make and when to make them.
Polymers are complex molecules composed of repeating subunits. The repeating subunits in DNA and RNA are called nucleotides.

                                           
      In 1953, James Watson and Francis Crick proposed a model for the DNA molecule that consisted of two nucleotide chains that wrap around each other to form a double spiral. This shape is called a double helix. The picture at the top of this page represents a double helix.  
                                           
                                                           
 

Each nucleotide has three parts:
1.   A Sugar

* Deoxyribose - a 5-carbon sugar in DNA
* Ribose - a 5-carbon sugar in RNA.
The "deoxy" prefix indicates the sugar in DNA
has less oxygen than regular ribose sugar

2.   One of these four nitrogen bases

* Purines - have a double ring of carbon and nitrogen atoms.
* Adenine
* Guanine
* Pyrimidines - have a single ring of carbon and nitrogen atoms.
* Thymine
* Thymine is replaced by uracil in RNA.
* Cytosine

3.   A phosphate group - PO4+3

       
                                 
                                                     
     

Base-pairing rules: these rules describe the behavior of the bases.

1. Cytosine (C) always bonds with guanine (G) by forming three hydrogen bonds.
2. Adenine (A) always bonds with thymine (T) by forming two hydrogen bonds.

A pair of bases that always bond together is known as a complementary base pair.

                                                     
               
  Replication the process of duplicating the DNA molecule.
An idea about size:
An average cell nucleus is about 6 micrometers in diameter.
The total length of the DNA in the human genome is 1.8 meters.
There must be several levels of coiling and supercoiling in DNA. 		 
               
                               
Chromosome:
a coiled, double rod-shaped form of condensed DNA that forms during cell division.
 
      DNA is normally found in long strands in the cell nucleus. The coiled structures we call chromosomes are found in cells only during cell division. DNA is duplicated prior to cell division. When the chromosomes form, one side of each chromosome consists of the original cell DNA while the other side consists of the duplicated DNA. One half of each chromosome goes to both cells during cell division. This insures that the new cell will have exactly the same genetic make-up as the original cell.        
                                                 
                                         
        The chromatid on the right shows the giemsa band pattern obtained by applying giemsa stain to chromosomes.
The dark bands are commonly called G-bands and the light bands are referred to as R-bands.
Cytogenetists use these predictable band patterns to look for alterations in chromosomes. 		       
         
                       
 
Humans have 46 chromosomes (23 pairs).
                       

Other important terms:

Gene - a segment of DNA on a chromosome that controls a particular trait.

Alleles - any of the several alternative forms of a Gene.

Chromatid - one of two identical halves of a chromosome.

Homologous chromosomes - the two members of each pair of chromosomes.

Diploid - 2N - a cell that contains both chromosomes of a homologous pair.

Haploid - N - a cell containing only one chromosome of a pair.
 

 
 
             

RiboNucleic Acid

RNA is responsible for the movement of genetic information from the DNA in the cell nucleus to the site of protein synthesis in the cytoplasm. RNA's sugar molecule is ribose instead of the deoxyribose sugar in DNA.
                 
                                     
   

Types of RNA:

1. Messenger RNA - mRNA - a single uncoiled strand that transmits information from DNA to the ribosomes during protein synthesis.
2. Transfer RNA - tRNA - a single folded strand that bonds with a specific amino acid.
3. Ribosomal RNA - rRNA - a globular form that is the major constituent of the ribosomes.

 
                                     
    Transcription - the process of forming a mRNA strand from a DNA strand.
* The DNA double strands are separated and a mRNA strand is formed by RNA bases pairing up with the exposed DNA sequence and each base linking to the next.
* The mRNA that is formed carries the genetic information that will be translated into a protein.
* The rate of transcription is about 40 nucleotides per second.
Protein synthesis the formation of proteins using information coded on DNA and carried out by RNA.
Translation the assembling of protein molecules from information encoded in mRNA. 		 
                       
                                                       
         

The central points on this page are:

1. DNA duplicates itself in replication.
2. DNA produces RNA in transcription.
3. RNA produces proteins in translation.
               
                                                           
         

Answer the following questions. Head your paper Unit 4 Day 1: DNA

1. What is the primary function of DNA?

2. How are the nitrogen bases in RNA different from the nitrogen bases in DNA?

3. How is the shape of the three types of RNA different?

4. The nitrogen bases of DNA always combine in specific pairs. Which bases always bond together?

5.DNA duplicates itself in _________________.

6. Use your own words to describe what happens in each of the following processes:

* replication
* transcription
* translation

7. Which series of bases will complete this strand of DNA?

A. CCTGAT
B. ACTGGC
C. GTAGGC
D. TCAGGG

 
                 
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