DNA structure, function, and replication

Where is DNA located in eukaryotic cells?

The nucleus

How many pairs of chromosomes do humans have?

23 pairs

What determines the biological sex in humans?

The presence or absence of the Y chromosome. Female is XX. Male is XY

Do all your body cells have the same DNA sequence?

No

List the three components of a nucleotide

A phosphate group, a five carbon sugar, and a nitrogenous base

Which nitrogenous bases are pyrimidines?

Cytosine, thymine, and uracil

Which nitrogenous bases are purines?

Adenine and guanine

State Chargaff’s rule

The rule states that the number of guanine units is equal to the number of cytosine units. And that the number of adenine units is approximately equal to the number of thymine units

If a DNA sample has 27% adenine, what percentage of cytosine does it contain?

2+27=54 I 100-54=46 I 46/2=23%

Why do G – C bases pair form stronger bonds than a – T pairs?

G – C bases are linked by three hydrogen bonds. A – T base pairs are only linked by two hydrogen bonds

What is meant by anti-parallel orientation in DNA strands?

The two strands of a double helix run in opposite directions

What does it mean that DNA replication is semi-conservative?

Each new DNA molecule is made up of an original parent strand in one new daughter strand

What are the raw materials required for DNA replication?

A DNA template, free nucleotides (A, T, C, G), and a deoxyribonucleotide triphosphaate

What direction is the template strand read?

3’ to 5’

What direction is the new DNA synthesised? 

5’ to 3’

What is the origin of replication?

 a sequence of DNA nucleotides where replication begin begins

What enzyme adds new nucleotides during replication?

 DNA polymerase

Why does DNA polymerase require an RNA primer to begin synthesis?

It can't cook from scratch

Which enzyme synthesize the RNA primer?

Primase

What type of bond joins nucleotides in a DNA strand?

A phosphodiester bond

What is the role of of helicase in replication?

To unwind the DNA double helix, and separate the two strands

What do single-stranded binding process proteins do?

They bind to and stabilize, single stranded DNA to protect it from damage and prevent re-annealing

What is the function of DNA polymerase III?

To synthesize new strands of DNA by adding nucleotides to a growing chain

What is the function of DNA polymerase I?

To remove RNA primers and fill the resulting gaps with DNA

What enzyme joints Okazaki fragments together?

DNA ligase

What strand is synthesize continuously?

The leading strand

What strand is synthesize discontinuously?

The lagging strand

What are Okazaki fragments?

Short segments of DNA synthesis on lagging strand

Explain why replication can only occur once per cell cycle

Because a two step process that involves a "licensing" phase in G1 and a “activation” phase in S

What is proofreading and which enzyme performs it?

It's an error-correcting process. DNA polymerase

How does mismatch repair differ from proofreading?

Mismatch is after DNA replication, proofreading is during

What is excision repair and when is it used?

A process that repairs damaged sections of DNA and replaces them. Occurs daily.

What are telomeres and why are they important?

They are caps on the ends of chromosomes that prevent the loss of genetic info.  To protect

What happens to telomeres as cells age?

They get shorter/smaller

What is the function of telomerase?

To maintain the length and integrity of chromosomes

What is the main purpose of PCR?

To make so many copies of a segment of DNA

What are the three steps of PCR?

Denaturation, annealing, and extention

Why is taq polymerase used in PCR?

It can withstand high temperature

What are the functions of in PCR?

1: to bind the start and end of a target DNA region

2: act as a starting point for DNA polymerase

How does PCR mimic natural DNA replication?

By using temperature

What are short tandem repeats?

A type of DNA sequence made of repeating units of 1–6 base pairs

Why are STR's useful for forensic identification?

They give a unique genetic profile. Their repetition count varies between individuals

How does PCR assist in DNA profiling?

It gives you more to work with by extending the sample and making it more detailed

What technique separates DNA fragments by size?

Gel electrophoresis

Why are STR banding patterns, unique for every individual except identical twins?

Because unrelated people almost certainly have different numbers of repeated units

Predict how in increasing G + C content affects DNA melting temperature

It would create more hydrogen bonds, have a higher stability, and increase the melting temperature

Describe what would happen to DNA replication if primase was nonfunctional

It would stop

Explain how UV radiation can damage DNA and how this damage is repaired

It is damaged by forming pyrimidine dimers, such as thymine dimers, which change the DNA helix and disrupt replication. This damage is repaired through photoreactivation

What is a Histone?

A single DNA molecule wrapped around proteins

Can errors in DNA be repaired?

No