FoB lecture 14 - cell cycle I - DNA replication & mitosis

What is the overarching concept when cells divide?

Two genetically identical sister cells are the products.

what does Interphase include?

G1, S, G2

What are the phases of the cell cycle?

G1 (gap 1), S (synthesis), G2 (gap 2), M (mitotic phase).

What occurs during the S phase of the cell cycle?

DNA replication occurs, creating two identical copies of the genome.

What is the significance of the G0 phase (gap 0)?

Differentiated cells exit the cell cycle and perform specific functions.

What types of bonds hold the DNA backbone together?

- Covalent phosphodiester bonds.

- hard to break apart

What types of bonds hold the two strands of DNA together?

- Hydrogen bonds between complementary base pairs (A+T & G+C)

- easier to break

what will we have in the middle when binding 2 strands of DNA together?

a pyrimidine with a purine

In which direction does DNA polymerase synthesize new DNA?

From 5' to 3'.

where do the proteins assemble at during DNA replication?

at the ORI

- this is where all the proteins start to bind & start to open the DNA to copy it

which cells tend to have circular chromsomes?

prokaryotes

- one origin of replication (ori) means one replication complex per chromosome

what shape are the chromosomes in eukaryotes?

- linear

- initiation in eukaryotes involves many thousands of ori sites on each chromosome

what is a centromere?

a small part of a chromosome that attaches sister chromatids to each other

what is chromatids?

one of two identical attached copies that make up a replicated chromosome

what do the 3 prime and 5 prime ends have?

5' end has a phosphate group (OPO3-)

3' has a hydroxyl group (OH)

why do we care about polarity of DNA strand?

because nucleic acids can only add onto the 3' prime end

What is the role of primase in DNA replication?

Primase lays down an RNA primer to provide a starting point for DNA polymerase.

What is the function of DNA helicase?

It separates the strands of the double helix during replication.

What is the purpose of topoisomerase during DNA replication?

It relieves strain caused by unwinding the DNA molecule.

What are Okazaki fragments?

Short segments of DNA synthesized on the lagging strand during replication.

What enzyme removes RNA primers during DNA replication?

DNA polymerase I.

What is the role of DNA ligase in DNA replication?

It creates covalent bonds between Okazaki fragments on the lagging strand.

What is semi-conservative replication?

The process where each new DNA molecule consists of one parent strand and one new strand.

what happens during telaphase?

nuclear envelope re-forms and chromosomes de-condense

What happens to DNA content after the S phase?

The DNA content of the cell is doubled.

What are sister chromatids?

Identical copies of a chromosome connected at the centromere after DNA replication.

What occurs during the mitotic phase?

DNA condenses and is divided equally into two daughter cells.

What is the function of histones in DNA organization?

organize DNA in the nucleus, helping to package it into a compact structure.

What is cytokinesis?

The division of the cytoplasm during cell division.

What is the significance of the antiparallel arrangement of DNA strands?

It creates different strategies for elongation during DNA replication.

What is the role of ssBinding proteins during DNA replication?

They stabilize single strands of DNA to prevent unwanted hydrogen bonds.

What is the template strand in DNA replication?

The existing strand of DNA that serves as a guide for synthesizing a new complementary strand.

what does DNA polymerase need to start adding nucleotides?

- it needs a double strand to bind to and provide the 3'-OH group

- DNA polymerase is not able to just start making a new strand without a 3 prime OH group to add onto

what happens once RNA primer is in place?

the DNA polymerase can add DNA bases complementary to the template strand

DNA polymerase cannot replicate DNA unless an RNA primer is first attached to the template strand. This is because DNA polymerase can only_____?

add onto existing hydroxyl groups

what 3 steps does the lagging strand elongation need more than the leading strand?

RNA primers between Okazaki fragments are removed

↓

DNA polymerase I comes and fills in the nucleotides that were once RNA

↓

DNA ligase creates covalent bonds in the backbone between Okazaki fragments

What happens to bacterial cells during division?

Bacterial cells divide but do not undergo mitosis.

What is the purpose of cell division?

Cell division allows for growth, repair, and reproduction of cells.

How similar is the DNA content of daughter cells after mitosis?

Daughter cells have identical DNA content to the parent cell.

What happens to the parent cell after mitosis?

The parent cell divides into two daughter cells.

What ensures that daughter cells receive the same genetic information?

DNA replication occurs without mutations.

What are the two ends of a single strand of DNA called?

The 5' end and the 3' end.

What does it mean for two polar strands of DNA to be arranged antiparallel?

One strand runs 5' to 3' while the other runs 3' to 5'.

What type of bonds hold the two DNA strands together in a double helix?

Hydrogen bonds between the nitrogenous bases of the nucleotides.

What are the initial steps involved in DNA replication?

Unwinding the DNA double helix

↓

stabilizing the replication fork

↓

synthesizing a primer

Why is a short RNA primer required for DNA elongation to begin?

The primer provides a starting point for DNA polymerase to synthesize new DNA.

What is the difference between the synthesis of leading and lagging strands?

- The leading strand is synthesized continuously

- while the lagging strand is synthesized in short fragments.

Why does a chromosome replicate in a semiconservative way?

Each new DNA molecule consists of one original strand and one newly synthesized strand.