A5 Nucleic Acids & DNA Replication

name the 2 types of nucleic acid and describe their basic functions

• DNA- holds genetic information which codes for polypeptides

• RNA- transfers genetic information from DNA to ribosomes

what are DNA and RNA made from

• polymers

• made up of many nucleotides

• joined together by phosphodiester bonds

• in a condensation reaction

• to form polynucleotide chains called nucleic acids

what 3 components is a nucleotide made from

1. phosphate group

2. nitrogenous base

3. pentose sugar

give 2 similarities between the DNA in eukaryotic cell and the DNA in prokaryotic cells

1. nucleotide structure is identical- deoxyribose attached to phosphate and a base

2. adjacent nucleotides joined by phosphodiester bonds, complementary bases joined by hydrogen bonds

3. DNA in mitochondria / chloroplasts have similar structure to DNA in prokaryotes

• short, circular, not associated with histone proteins

what is a polynucleotide another name for

nucleic acid

give 4 differences between the DNA in eukaryotic cell and the DNA in prokaryotic cells

1. eukaryotic DNA is longer

2. eukaryotic DNA is linear, prokaryotic DNA is circular

3. eukaryotic DNA is associated with histone proteins, prokaryotic DNA isn’t

4. eukaryotic DNA contain introns, prokaryotic DNA does not

how do nucleotides join together and what bond is formed

• condensation reaction, removing water molecule

• between phosphate group of one nucleotide

• and pentose sugar of another

• forming a phosphodiester bond

what type of pentose sugar is found in DNA

deoxyribose

what type of pentose sugar is found in RNA

ribose

what is a chromosome

• long, linear DNA which is associated with histone proteins

• in the of nucleus of eukaryotic cells

what is a gene?

a short section of DNA that codes for the amino acid sequence of a polypeptide or a functional RNA e.g. tRNA

what is a locus?

fixed position a gene occupies on a particular DNA molecule

describe the complementary base pairing in DNA

• purine adenine pairs with pyrimidine thymine forming 2 hydrogen bonds

• purine guanine pairs with pyrimidine cytosine forming 3 hydrogen bonds

what 2 types of bond are present in DNA

phosphodiester bonds:

• strong bonds between sugar and phosphate

• formed in condensation reactions

• DNA polymerase enzyme catalyses the formation of this bond

hydrogen bonds

• weak bonds between bases of DNA

• join 2 strands together

what does it mean when DNA is described as antiparallel

• two strands form a double helix

• each strand running antiparallel to the other

how does the structure of DNA make it well suited to its job of storing and expressing genetic information

1. very stable molecule

2. two complementary strands mean there are 2 copies of info, useful for repair, copying and error checking

3. DNA is very long molecule so it stores lots of info

4. four different bases, can appear in any order so their sequence can encode info

describe the structure of DNA (5)

1. polymer of nucleotides

2. each nucleotide formed from deoxyribose sugar, a phosphate group and a nitrogenous base

3. phosphodiester bonds between adjacent nucleotides

4. double helix / double stranded

5. 2 polynucleotide chains held together by weak hydrogen bonds

6. between complementary base pairs→ adenine- thymine and cytosine- guanine

why do organisms need to be able to make new cells

• growth

• replace dead cells

• replace damaged tissues

describe how DNA is replicated ( semi conservative replication )

model ans M.S.

1. DNA helices breaks hydrogen bonds break between bases and strands separate

2. each strand acts as a template

3. free nucleotides attach to exposed bases

4. complementary base pairing (AT and CG)

5. DNA polymerase joins adjacent nucleotides on a new strand together by condenstation reactions

6. forming strong phosphodiester bonds

7. H bonds reform

8. semi conservative replication

read over the Meselson Stahl experiment a evidence for semi conservative replication

okay

explain how the structure of DNA is related to its functions- model ANS PPQ (5)

1. double helix with sugar phosphate backbone→ so protects bases

2. large / long molecule→ stores lots of genetic information

3. coiled into a double helix→ compact

4. base sequence codes for amino acids

5. double stranded→ both strands can act as templates for semi conservative replication

6. weak hydrogen bonds between bases for strand separation

7. complementary base pairing → accurate replication

8. many hydrogen bonds between bases→ stable / strong molecule

name the 2 types of molecule from which a ribosome is made

• RNA

• proteins

learn to draw and label a DNA and an RNA nucleotide

okay

describe the structure of (m)RNA

• polymer of nucleotides

• each nucleotide formed from ribose, a phosphate group and a nitrogen containing organic base

• bases- uracil, adenine, cytosine, guanine

• phosphodiester bonds join adjacent nucleotides

• single helix

compare and contrast the structure of DNA and (m)RNA

1. DNA- pentose sugar is deoxyribose, RNA- pentose sugar is ribose

2. DNA has base thymine, RNA- has base uracil

3. DNA is double stranded, RNA- single stranded

4. DNA- long (many nucleotides), RNA- shorter (fewer nucleotides)

5. DNA- has hydrogen bonds, RNA- doesnt

why is semi conservative replication important

ensures genetic continuity between generations of cells

define what semi conservative means

each new DNA molecule consists of one original strand and one new strand

use your knowledge of enzyme actions to suggest why DNA polymerase moves in opposite directions along DNA strands

• DNA has antiparallel strands

• so arrangements of nucleotides on two ends are different

• DNA polymerase is an enzyme with a specific shaped active site

• so can only bind to substrate with complementary shape