Unit 6: Cell Reproduction

What is a checkpoint?

-critical point stop where stop and go signals regulate the cycle -many signals come from cellular surveillance mechanisms -indicate whether key processes have been done correctly

What is the difference between chromatin and chromosomes?

Chromatin is DNA coiled around proteins while Chromosomes are supercoiled chromatin.

When do you have actual chromosomes in your cell?

Chromosomes condense only for DNA replication, the rest of the time it is in chromatin form.

What are cyclins? What do they do?

Cyclins are groups of proteins that are rapidly made and destroyed at certain points in the cycle. They regulate the timing of the cell cycle in eukaryotic cells.

What type of asexual production occurs in prokaryotes? Eukaryotes?

Prokaryotes: Binary Fission Eukaryotes: Mitosis

Describe the DNA replication process in prokaryotes.

Replication begins at a single point and proceeds in two directions simultaneously until the DNA is copied.

What are single strand binding proteins for?

Single strand binding proteins hold the DNA strands separate and untwisted.

Know what happens in each phase of the cell cycle

(interphase is in slide 33) MITOSIS: Prophase: -longest phase of mitosis -centrioles move towards opposite sides of nucleus -chromatin condenses into chromosomes -nuclear envelope breaks down -can be broken down into "early" and "late" based on the condensation of the chromosomes and the location of centrioles Metaphase: -only lasts a few minutes -chromosomes line up in the middle of the cell; microtubules connect the centrosomes of the chromosomes to the spindle fibers Anaphase: -centrosomes that join together the sister chromatids break apart to become individual chromosomes -chromosomes move apart until they reach the centriole near the end of the spindle -ends when centrioles stop moving Telophase: -the chromosomes begin to tangle back into chromatin and lose their visibility -a nuclear envelope begins to re-form around each set of chromosomes -spindle breaks apart and nucleoli becomes visible in each cell nucleus -END OF MITOSIS!!!

How do plants and animal cells differ in cytokinesis?

-Animals cells: happens when cell membrane is drawn in (cleavage furrow) and the cell cleaves into two cells -Plant cells: a cell plate forms between two nuclei and eventually becomes a dividing membrane

What are the 3 reasons large cells need to divide?

-DNA overload= large cells can't control their functions as well as small cells -large cells can't exchange materials as well (the ratio of surface area (cell membrane): volume decreases as cell gets bigger, makes it harder for food to get in and wastes to go out; volume increases faster than surface area -as cells age, they're not as efficient

What are internal regulators?

-Proteins that respond to events inside of the cell

What is anchorage dependence?

-cells have to be attached to a sublayer to grow

Which enzyme cuts out damaged section of DNA during excision repair?

Exonuclease/nuclease

What is the M checkpoint for?

-makes sure all the chromosomes are aligned on the spindle in the middle of the cell and spindle fibers are properly attached and ready for cell division before anaphase begins

What are external regulators?

-proteins that respond to events outside of the cell -direct cells to speed up or slow down the cycle

What are telomeres, where are they located, and what is their purpose?

-region of repetitive DNA (non-coding) allows the DNA to replicate all genetic info without replacing entire chromosome -located at both ends of the chromosome -also prevents chromosome fraying and chromosomes from falling apart and attaching to each other

What is density-dependent regulation?

-when cells come in contact with other cells they stop growing Example: cells in a petri dish will grow until they form a single layer covering the bottom of the dish. If you remove a strip of cells, they will divide to cover the open space, and stop growing when they come in contact with other cells

New nucleotides are added to which end of the growing DNA molecule?

3' end

This means that the new strand grows in the ___ -> ___ Direction.

5' -> 3' Direction

Messelsson and Stahl showed that DNA replication is semi-conservative. What does that mean?

A parent strand is used as a model while new nucleotides attach.

These sites open into bubbles. Compare prokaryotes and eukaryotes in terms of these bubbles.

As the 2 DNA strands open at the origin, replication bubbles form. Eukaryotes have many bubbles while prokaryotes (bacteria) have a single bubble.

Why do cancer cells grow uncontrollably?

Cancer cells don't respond to the signals that regulate the growth of normal cells.

What is cancer?

Cancer is a disorder of uncontrolled cell growth in which some of the body's own cells lose the ability to control growth

What do centrioles and spindle fibers do?

Centrioles and spindle fibers are a part of your cytoskeleton. Spindle fibers connect to chromosomes to separate them during cell division.

Describe the structure of a chromatin (include the words histone and nucleosome).

Chromatin consists of DNA tightly coiled (wrapped) around proteins called histones. It's wrapped 2 times around 8 histones to form nucleosomes and the nucleosomes are wrapped up to form chromatin.- a thick, ropy fiber.

Which enzyme proofreads for DNA errors?

DNA Polymerase

What job does DNA polymerase do?

DNA Polymerase adds new nucleotides, it removes the RNA primers and proofreads the DNA for errors.

Where does DNA replication begin in eukaryotes? How many sites are there?

DNA in eukaryotes begin at the origin of replication. There are hundreds of origin of replication sites.

When must DNA replication occur during the life of a cell? Why?

DNA replication has to occur before a cell divides in the form of chromatin, so then the daughter cells each have their own genome.

How many pairs of chromosomes does each human have? How many in total?

Each human has 23 pairs of chromosomes. Each human has 46 chromosomes in total.

What happens at the G1 checkpoint if a cell gets a go-ahead signal? What happens if it doesn't?

G1 GO: completes the rest of the cycle and divides NO: cell exits the cycle and goes to a non-dividing stage called the G0 phase (most human cells are in this phase; nerve cells and heart muscle cells are usually in this phase)

When are growth factors important?

Growth factors are important external regulators. They stimulate the growth and division of cells. It's important during embryonic movement and wound healing.

What does helicase do?

Helicase unwinds and separates the 2 DNA strands by breaking weak hydrogen bonds.

What are homologous chromosomes?

Homologous chromosomes are chromosomes that are identical in shape, size, same genes and same location.

What is a tumor?

Masses of cancer cells

Do all eukaryotic cells do mitosis?

Mitosis doesn't occur in nerve cells, muscle cells and red blood cells.

What is the acronym for mitosis? For the whole cell cycle?

Mitosis: PMAT Cell Cycle: IPMATC

What are the lagging strand fragments called?

Okazaki Fragments

What does primase do?

Primase is the enzyme that synthesizes the RNA Primer. The primer is about 10 nucleotides long.

Do prokaryotes or eurkaryotes perform DNA replication rapidly?

Prokaryotes

How do the daughter cells of mitosis compare to each other and to the parent cell?

The daughter cells have the same number of chromosomes as each other and their parents cells. They have the same genes as the parents cells as each other. The daughter cells are completely identical and they're also identical to their parent cells, but the daughter cells are smaller.

What is the difference between leading and lagging strands? How and Why are they made differently?

The leading strand is synthesized continuously as a single strand from the point of origin toward the opening replication fork. The lagging strand is synthesized discontinuously against the direction of replication. The strands are made in different ways because nucleotides are added to the 3' end, but the strands are antiparallel. They're also only added in the 5' to 3' direction.

What happens to the RNA primer at the end of replication?

The primer will be removed and replaced with DNA.

After primers have been replaced with DNA nucleotides, what must ligase do?

The segments of sugar-phosphate backbone are sealed by ligase, which include all fragments of lagging strand and sections of primer replaced by DNA nucleotides.

What are replication forks?

The sites where separation and replication occur (y-shaped region)

Why are new cells made?

They're produced for growth and to replace damaged or old cells.

What happens during the 3 parts of interphase?

When a daughter cell is formed, it immediately starts it's life cycle at interphase. Three parts of interphase: G1, S and G2 G1: -cell spends most time here -cells do most of their growing -make new proteins and organelles S: -DNA replication happens here, so each daughter cell has own copy -once this phase begins, the cell is ready for mitosis G2: -cell grows a little more -cell makes organelles and molecules required for mitosis -Once G2 ends, mitosis begins

XX= ______ and XY=______

XX= female, XY= male

Mitosis is the division of ...

a cell's nucleus and cytoplasm in order to form two new cells.

What is the difference between autosomes and sex chromosomes? Which chromosomes are autosomes? Which chromosomes are sex chromosomes?

autosomes- code for most of offspring traits (chromosomes 1-22) sex chromosomes- code for sex of the offspring (23rd set of chromosomes