DNA Structure and Replication

What does DNA stand for?

Deoxyribonucleic Acid

“Deoxy”

Missing an oxygen atom (on the sugar)

“Ribo”

Refers to ribose sugar

“Nucleic”

Found in the nucleus 

“Acid”

Due to the phosphate groups

Where do the atoms of DNA appear in 3D space? (2)

Phosphorus - Outer edges

Oxygen - Outer edges

Hydrogen - Mostly outer, some inner

Nitrogen - Mostly inside

What parts of a DNA molecule make up the backbone?

• Phosphate groups

• Deoxyribose sugars

What do phosphate groups contain?

• Phosphorus

• Oxygen

What traits define the general structure of DNA?

• Double-stranded

• Helix

• Strands are complementary and antiparallel (run in opp directions)

What’s important to know about the polarity of DNA?

• Each strand has polarity → a 5’ end and a 3’ end

• The complementary strand has the opposite polarity → essential for replication

What are the subunits of DNA?

• Nucleotides 

  • A phosphate group

  • A 5-carbon sugar

  • A nitrogenous Base

What are the four DNA bases and how do they pair?

• Adenine (A) pairs with Thymine (T) - 2 hydrogen bonds 

• Guanine (G) pairs with Cytosine (C) - 3 hydrogen bonds (stronger)

What types of bonds hold DNA together?

• Hydrogen bonds → between bases

• Covalent bonds → in the sugar-phosphate backbone

• Phosphodiester bonds → connecting nucleotides in the backbone

What are phosphodiester bonds?

Special covalent bonds connecting nucleotides in the backbone

What does “semiconservative replication” mean?

Each new DNA molecule has one old (parental) strand and one new strand

What is the first step of semiconservative replication?

Start with the parental DNA molecule and its complementary strands

What is step two of semiconservative replication?

The strands gets separated each becomes a template for a new strand

How is DNA read in semiconservative replication?

5’ → 3’ so the opposite strand runs in the other direction

What is step 3 of semiconservative replication?

Two identical daughter DNA molecules form - each with one old and one new strand

What enzyme is needed for DNA replication?

DNA polymerase

• adds new nucleotides to form the new strand

What does helicese do in DNA replication?

Unwinds and separates the two DNA strands by breaking hydrogen bonds

How is DNA packaged in the cell?

DNA wraps around special proteins, forming chromosomes

How many pairs of chromosomes do humans have?

23 pairs (46 total) 

What pair of chromosomes determines biological sex?

The 23rd pair

Where do our chromosomes come from?

One chromosome of each pair comes fro each parent

What is a genome?

The complete collection chromosomes (all DNA) in a organism 

What does “sequence” mean in DNA?

The order of bases, as it determines a person’s genetic traits

What is Polymerase Chain Reaction (PCR)?

A laboratory technique used to replicate DNA when only a small sample is available

What ingredients are needed for PCR?

• Og DNA sample

• Free nucleotides 

• DNA polymerase 

• Primers 

What is DNA polymerase?

Heat-tolerant enzyme

What are primers?

Short DNA pieces that guide replication

How does PCR work?

S1 - Heat - separates DNA strands 

S2 - Cool - primers attach to the strands

S3 - Warm - polymerase adds new nucleotides 

What is DNA profiling?

Technique used to identify unique genetic features in a person’s DNA

What are STRs and why are they used in DNA profiling?

• Short sequences of DNA repeated multiple times in a row

• The number of repeaters varies among people (why it’s important for identification)