3.1.5 Nucleic acids are important information-carrying molecules Flashcards
What is DNA ?
DNA is the genetic material found in all living organisms, ranging from single-celled
bacteria to multicellular mammals
Where is DNA found ?
Found in the nucleus of eukaryotes and in the
organelles, chloroplasts, and mitochondria. In prokaryotes, the DNA is not enclosed in a
membranous envelope
What is the biological process RNA is involved in ?
protein synthesis
What monomers are DNA and RNA made of ?
nucleotides
What are the three components of a nucleotide ?
- a pentose sugar (made with 5 carbon atoms)
- a nitrogenous base
- a phosphate group
What sugar and bases does a DNA nucleotide have ?
Deoxyribose , adenine (A), thymine (T), cytosine (C), and guanine
(G).
What sugar and bases does RNA nucleotide have ?
Ribose ,the base uracil (U) replaces thymine (T) A , C and G
Compare DNA to RNA
DNA :
Deoxyribose sugar
Double stranded
Thymine
Similarities:
Nucleic acid
Adenine Phosphate
Guanine
Cytosine
RNA:
Ribose sugar
Single stranded
Uracil
What is a polynucleotide ?
polymer of nucleotides
How do nucleotides join together ?
Nucleotides join via a condensation reaction between the phosphate group of one
nucleotide and the sugar of another.
What chemical bond forms between nucleotides ?
This forms a strong, covalent, phosphodiester bond (which consists of the
phosphate group and two ester bonds).
What is the chain of sugars and phosphates known as ?
sugar-phosphate backbone
Fill in the gaps
When a polynucleotide is formed, the __ phosphate of the incoming nucleotide
attaches to the _ hydroxyl group at the end of the growing chain.
When a polynucleotide is formed, the 5′ phosphate of the incoming nucleotide
attaches to the 3′ hydroxyl group at the end of the growing chain.
What is the structure of DNA ?
DNA is made of two polynucleotide chains in a double-helix structure.
What bonding joins the two polynucleotide chains in DNA ?
hydrogen bonding between
bases
When each base can only pair with one particular partner what is this key term ?
complementary
base pairing
How many hydrogen bonds do adenine and thymine form ?
2
How many hydrogen bonds does cytosine and guanine form ?
Three
In semi-conservative replication how many strands can be templates ?
2
What is RNA ?
Short, single polynucleotide chain much shorter than DNA
Why is DNA replication called semi-conservative ?
because half the strands in each new DNA
molecule come from the original DNA molecule
Describe the process of semi-conservative replication
The DNA replication process
1. The enzyme DNA helicase breaks the hydrogen bonds between the base pairs on
the two polynucleotide DNA strands. This unwinds the helix to form two single
strands.
2. Each original single strand acts as a template for the new strand. Complementary
base pairing means that free-floating DNA nucleotides are attracted to their base
pair - A with T and C with G
3. Condensation reactions join the nucleotides of the new strands together using the
enzyme DNA polymerase as the catalyst. Hydrogen bonds form between bases on
the original and new strands
4. Each new DNA molecule contains one strand from the original DNA molecule and
one new strand
Who proposed the semi conservative DNA replication theory and who validated it ?
Watson and Crick - proposed
Meseleon and Stahl - proved
Describe the Meselon-Stahl experiment
Meselson and Stahl experimented with E. coli grown first in heavy nitrogen (15N)
then in 14N
‒ DNA grown in 15N (red band) is heavier than DNA grown in 14N (orange band), and
sediments to a lower level in cesium chloride solution in an ultracentrifuge
‒ When DNA grown in 15N is switched to media containing 14N, after one round of
cell division the DNA sediments halfway between the 15N and 14N levels, indicating
that it now contains fifty percent 14N.
‒ In subsequent cell divisions, an increasing amount of DNA contains 14N only.
‒ This data supports the semi-conservative replication model