Lecture 9

Define Genetics:

Study of the transmission of traits (alleles) from one generation to the next (i.e. from parents to offspring)

Define Genomes:

Sum total of genetic material of an organism

Most of the genome exists in the form of?

chromosomes

Some genomes appear as?

Plasmids or in certain organelles of eukaryotes (mitochondria and chloroplasts)

Genome of cells composed exclusively of?

DNA

Genome of viruses can contain either?

DNA or RNA

Describe DNA:

• Makes up Chromosomes

• Found in bacteria and eukaryotes

Define Characteristic:

a feature of an organism

Ex: Height, hair color, etc.

Define Trait:

a particular version of that characteristic

Ex: 6’3 in height; black hair color

Define Gene:

A sequence of DNA that codes for a feature of an organism

• There is at least one gene for every feature (characteristic)

Define Allele:

Alternative versions of the same gene 

• There are usually at least 2 alleles for every gene (two parents)

Define Genotypes:

Combination of alleles that you possess

Define Phenotype:

The physical expression of the genotype is called the phenotype (an organism’s appearance)

What are the 3 types of Genes?

• Structural → proteins

• RNA machinery

• Regulatory genes

Humans have how many genes?

~20k genes

Viruses have how many genes?

3-4

E. Coli. has how many genes?

4000 genes

What is a DNA structure made up of?

• Phosphate

• Deoxyribose

• Nitrogenous base

  • Purines (AG)

  • Pyrimidines (CT)

VERY IMPORTANT: DNA Structure is created with what dimensions?

Created in 5’ → 3’

Describe DNA structure:

• Antiparallel strands

• Created in 5’ → 3’

• Double strands held together by hydrogen bonds aka bases (C-G + A-T)

How many enzymes is involved in DNA replication?

-30 Enzymes

Define Semiconservative replication:

• Strands separated and 2 daughter complementary strands produced

• Neither is completely new; one strand that serves as a template is an original parent of the DNA strand

New strands from DNA Replication are always?

synthesized 5’ → 3’

Why does each daughter cell gets a strand from the previous cell?

To reduce error - to make sure the original is maintained

The origin of replication is a?

Short sequence rich in adenine and thymine bases

A-T base pairs are held together by?

Only two hydrogen bonds rather than three

Because the origin of replication is AT-rich, less energy is required to?

Separate the two strands than would be required if the origin were rich in guanine and cytosine

Topoisomerases function during replication:

Unwind the DNA helix, giving helicases access to bind to the dsDNA at the origin

Define helicases:

Unzipping Enzymes

Helicases function:

Break the hydrogen bonds holding the two strands together, resulting in two separate strands → becomes Y shape fork

What keeps the two replicated strands apart?

Single-strand binding proteins

After unzipping, DNA polymerase III adds?

Nucleotides in accordance with the template pattern

During DNA polymerase’s following of template pattern, what has already been added to a short length of RNA?

RNA primase

DNA polymerase is correctly oriented for?

Synthesis only

What strand of new DNA called be synthesized into a continuous + complete strand?

The leading strand

→ The strand going in 5′ to 3′ direction

What strand of new DNA is termed the “Lagging Strand?”

The strand with the opposite orientation (3′ to 5′)

B/c Lagging Strand is opposite orientation, Polymerase?

Can only add a few nucleotides at a time in the direction away from the fork (5′ to 3′)

As the fork opens up a bit, the next segment is synthesized?

Backward to the point of the previous segment → repeat until synthesis is complete

Why does the DNA polymerase synthesize backwards?

Wants to synthesize the two new strands simultaneously, despite other one taking longer

Backwards synthesis by DNA polymerase produces?

One strand containing short fragments of DNA (100 to 1,000 bases long) called Okazaki fragments.

Okazaki fragments are attached to growing end of Lagging Strand + put together by?

Enzyme called DNA Ligase

Helicase function:

Unzipping the DNA helix

Primase Function:

Synthesizing an RNA primer

DNA polymerase III Function:

Adding bases to the new DNA chain; proofreading the chain for mistakes

DNA polymerase I Function:

Removing primer, closing gaps, repairing mismatches

Ligase Function:

Final binding of nicks in DNA during synthesis and repair

Topoisomeriase I and II Function:

Supercoiling and untangling