Unit 3: DNA & RNA

Why DBA replication is needed

1. production of gametes - sex cells during meiosis

2. Growth + repair of tissue - mitosis

Semi - conservative

Replication of DNA - one old + one new strand

When cell = ready to divide - 2 strands of double helix = seperate

Each of original strands acts as template for the creation of a new strand

new strands = assembled through complimentary base pairing

DNA Replication

• Unwinding + unzip double helix with enzyme HELICASE

• Unzips to position called replication fork

• Nucleotides base pair through complementary base pairing

• DNA Polymerase joins together nucleotides - strong phosphodiester bonds

• DNA polymerase only adds nucleotides in 5’ to 3’ direction

• Double strand reforms a double helix

Polymerase chain reaction

• Used for making copies of DNA artificially

• Used to amplify/make millions of DNA copies

• Taq polymerase = heat resistant version of DNA polymerase

• PCR = Cloning DNA at rapid speed

• Temperature used instead of enzymes to break H bonds - 95 degrees

Gel Electrophoresis

• Fragments of DNA move in electrical field and are separated

• Separation = based on size/mass

• Sample of DNA = placed on wells ong el

• Electrical current = passed across gel

• DNA = negatively charges - when electrical current is passed through

  • DNA fragments move to positive electrodes

• Large Fragments move slow

• Small fragments move quicker

Gel electrophoresis used in DNA profiling

• Used to differentiate between individuals

• Technique can be used for:

  • Forensic crime investigations - see if suspects DNA match DNA on scene

  • Parentage issues

  • Animal breeding

  • Disease detection

HL - DNA replication

• Takes place during S section of interphase

• 5’ to 3’

• Antiparallel strands

1. Replication begins at sites ‘origin of replication’

2. Helicase attaches + unzips and unwinds - breaks hydrogen bonds

3. Gyrae keeps DNA strands separated

4. RNA Primase synthesises small amount of RNA primer (will be changed to DNA)

5. DNA polymerase III can only join Nucleotides in 5’ to 3’

   1. only nucleotides can join to 3’ end called leading strand

1. On other side DNA polymerase works away from replication fork

2. Create small fragments - Okazaki fragments - Lagging strand

3. Several primers - one between each fragment

4. Enzyme Ligase joins okazaki fragments to form one continuous DNA molecule

5. DNA polymerase I replaces RNA primer with DNA

DNA polymerase 3 can check its work and repair mismatched bases

What is the full name of DNA

deoxyribonucleic acid

What does DNA carry?

the genetic code for all living organisms

What is the genetic code said to be?

Universal

Where is DNA usually found?

In the nucleus

Apart from the nucleus, where else could DNA be found?

in the chloroplasts or the mitochondria

What is the full name for RNA?

Ribonucleic Acid

What is RNA the main component of?

Ribosomes

Apart from ribosomes, where else is RNA found?

in the cytoplasm and the nucleus

Are viruses considered living?

No

What are RNA and DNA?

Polymers

What are the subunits of DNA and RNA?

Nucleotides

What are the components of nucleotides?

A pentose sugar, nitrogenous bases, and a phosphate group

What are the two type of pentose sugars?

ribose and deoxyribose

What pentose sugar does RNA have?

ribose

What pentose sugar does DNA have?

deoxyribose

What are the two types of nitrogenous bases?

Purines and Pyrimidines

What are the purines?

A and G

What are the pyrimidines?

T and C

What distinguishes purines and pyrimidines?

purines have two rings, pyrimidines have one

What are the nitrogenous bases for DNA?

A, G, C, T

What are the nitrogenous bases for RNA?

A, G, C, U

What are the full names of all the bases?

Adenine, Guanine, Cytosine, Thymine, Uracil

What is the chemical formula for a phosphate group?

PO₄⁻

What are the complimentary bases in DNA

A and T are complimentary, G and C are complimentary

Draw a Nucleotide

What is the DNA backbone (show on diagram)

How is the bond between the phosphate group and carbon 3 on the pentose sugar made?

Condensation

What is a polymer of nucleotides (forming a nucleic acid) known as?

a strand

Describe the structure of ribonucleic acid

Relatively short, a single-stranded polynucleotide, with ribose as the pentose sugar

What is the name of the bond between a carbon atom of a pentose sugar and the phosphate group?

A phosphodiester bond

Draw the formation of a phosphodiester bond

What are the three types of RNA?

messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRna)

What is the role of tRNA?

transports amino acids to ribosomes during protein synthesis

Define mRNA

formed in the nucleus and transported to the ribosomes in the cytoplasm

What is the use of rRNA?

forms part of ribosomes

Define the structure of DNA

A double helix made of two anti-parrallel strands of nucleotides linked by hydrogen bonds between complimentary nitrogenous base pairs.

How many hydrogen bonds are between A and T?

2

How many hydrogen bonds are between G and C?

3

What are the three main differences between DNA and RNA?

in RNA the pentose sugar is ribose, in DNA the pentose sugar is deoxyribose

In RNA there’s no base thymine, instead there’s uracid, in DNA there’s no base uracil, instead there’s thymine

RNA is single stranded, DNA is double stranded

What are the three roles of bases pairing?

DNA replication, transcription, and translation

Define briefly the role of base sequences in DNA replication

the base sequences in DNA can be accurately copied so the genetic information of a cell can be passed on to daughter cells

Define briefly the role of base sequences in DNA transcription

RNA can be made of the same base sequence as 1 of the DNA strands, mRNA carries the sequence of a the protein coding gene to the ribosome

Explain (in detail) translation using complimentary base pairs and codons

A base sequence can be used to determine the the amino acid sequence in a polypeptide. mRNA has a three-base codon, tRNA carries a three-base anticodon and 1 amino acid. Ribosomes link condons to anti-codons by complimentary base pairing

What is the formula for the number of base pairs?

4ⁿ

How much information can be stored in DNA?

A limitless amount

how many codons are there?

64

How do codons provide proof of LUCA?

There are billions of ways to assign meaning to codons, but all living organisms do the same way (with slight variation)

What is the use of codons?

They can indicate any one of the amino acids

Where does the phosphate group form a bridge between when linking nucleotides?

Carbon 3 and Carbon 5

What is the name of the ends of nucleotides?

3’ and 5’

What molecule is at each end of the nucleotide?

OH

Draw a single strand nucleotide showing 3’ and 5’

Explain the advantages of having a purine attach to a pyrimidine?

The width is always the same creating a stable molecule

explain the role of a nucleosome

A disc-like structure which packages DNA into a condensed chromosome which allows the control of replication and transcription

Define the structure of a nucleosome

8 histone proteins in it’s core with DNA wound twice around it and held together by an additional histone protein.

What is the name of the experiment that found that genes came from DNA and not proteins?

the Hershey-Chase experiment

What radioactive isotopes were used in the Hershey-Chase experiment?

³⁵S and ³²P

What bacteria was used during the Hershey-Chase experiment?

E. Coli

What element does DNA contain that proteins don’t?

Phosphur

What element does protein contain that DNA doesn’t?

Sulfur

What is the supernatant?

The liquid

What is the relationship between the percentages of bases A and G?

Their sum equals 50%

What is the relationship between the percentages of bases T and C?

Their sum equals 50%

What is the relationship between the percentages of bases G and C?

They’re equal

What is the relationship between the percentages of bases A and T?

They’re equal