Bio Unit 6 - Cell Cycle

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

All segments of the sugar-phosphate backbone are sealed by ligase. This Includes: All fragments of lagging strand. Sections of primer replaced by DNA nucleotides.

What is the difference between chromatin and chromosomes?

Chromosomes are super cooled chromatin; chromatin is DNA wound around proteins.

When do you have actual chromosomes in a cell?

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

What are external regulations?

External Regulators: proteins that respond to events outside the cell, and direct cells to speed up or slow down the cell cycle

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

Semi-Conservative Hypothesis - A parent strand is used as a model while new nucleotides attach. This means that each new piece of DNA has one original strand, and one new strand.

Prophase - "pile" of chromosomes:

Prophase is the longest phase of mitosis. During prophase: • The centrioles lineup on opposite sides of the nucleus. • Spindle fibers made of microtubules form, and are organized by the centriole. • The chromatin condenses into visible chromosomes. • Nucleolus disappears and nuclear envelope breaks down. • Prophase can actually be broken down into "early" and "late" based on the condensation of the chromosomes and location of the centrioles.

What are single-stranded binding proteins for?

Single-Stranded Binding Proteins attach and keep the 2 DNA strands separated and untwisted (like thumb tacks).

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

Eukaryotes - many bubbles Prokaryotes - one bubble

What type of asexual reproduction occurs in prokaryotes? Eukaryotes?

Eukaryotes: Mitosis. Prokaryotes: Binary Fission.

Give 3 reasons why large cells need to divide. Explain each!

1. Large cells can't control their functions as well as small cells = DNA overload. • as a cell gets bigger, it still has the same amount of DNA to do the same jobs, but there are more jobs to do. 2. Large cells can't exchange materials as well. • the ratio of surface area (cell membrane) to cell volume decreases as a cell gets bigger, making it harder for good to get in and wastes to go out (volume increases faster than surface area) 3. As cells age, they aren't as efficient.

Explain the difference between autosomes and sex chromosomes.

22 of the homologous pairs match more or less exactly (the autosomes), the 23rd pair (sex chromosomes) will match if it's XX (female) but be different if it's XY (male).

How many pairs of chromosomes do humans have? How many total?

23 pairs; 46 total.

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

3' end.

New nucleotides added to the 3' end of the growing DNA molecule means the new strand grows in what direction?

5' —-> 3'.

What is a checkpoint?

A checkpoint in the cell cycle is a critical control point where stop and go signals regulate the cycle. Many signals registered at checkpoints come from cellular surveillance mechanisms. These indicate whether key cellular processes have been completed correctly.

How do plant and animal cells differ in cytokinesis?

Animals: Cytokinesis happens when the cell membrane is drawn in = cleavage furrow, and the cell cleaves into two new cells. Plants: A structure made of wall-building vesicles, called a cell plate forms between the two new nuclei, and eventually becomes a dividing membrane.

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

Before cell division, so that each daughter cell gets a complete copy of the genome.

What does primase do?

Before new DNA strands can form, there must be RNA primers (short RNA sequences) present to start the addition of new nucleotides. Primase is the enzyme that synthesizes the RNA Primer. The primer is about 10 nucleotides long.

Why do cancer cells grow uncontrollably?

Cancer cells do not respond to the signals that regulate the growth of most cells.

What is cancer?

Cancer: A disorder 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 part of your cytoskeleton. Spindle fibers connect to chromosomes to separate them during cell division.

Describe the structure of chromatin. Include the words histone and nucleosome.

Chromatin consists of DNA tightly coiled around proteins called histones. DNA is wrapped around histones to form nucleosomes. The nucleuosomes are wrapped up to form chromatin - a thick, ropy fiber.

What are cyclins? What do they do?

Cyclins: A family of proteins found in cells that is present in large amounts during cell division, and very small amounts the rest of the time. Cyclins regulate the timing of the cell cycle in eukaryotic cells.

Which enzyme proofreads DNA for errors?

DNA polymerase.

What are replication forks?

DNA replication begins at origins of replication. Two strands open forming replication forks (Y-shaped region). New strands grow at the forks.

What is density-dependent regulation? Explain how it works.

Density-Dependent Regulation: Cells stop growing when they come in contact with other cells. • 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. In our bodies, if we are injured, the cells near the injury are stimulated to divide rapidly to close the wound, and slow down or stop dividing when it is done.

Do all eukaryotic cells do mitosis?

Doesn't occur in some cells such as nerve cells, muscle cells, and red blood cells.

Anaphase - sister chromatids move "away" from each other:

During anaphase: • The centromeres that join sister chromatids separate and the chromatids become individual chromosomes. • The chromosomes move apart until they reach the centrioles near the end of the spindle. • Anaphase ends when the centrioles stop moving.

Telophase - "two" nuclei are visible:

During 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. • The spindle breaks apart. • Nucleoli become visible in each new nucleus. • This is the end of mitosis! Cytokinesis: the actual cell divides

What does helicase do?

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

Describe what happens during each of the three parts of interphase.

G1 Phase = Primary Growth • in G1, cells do most of their growing • cells also synthesize new proteins and organelles in G1 S Phase = Synthesis • in S, cells replicate their DNA so that they have a copy for each new daughter cell • once S Phase begins, it is ready for mitosis G2 Phase = Secondafy Growth • in G2, the cell grows a little bit more • the cell also makes the organelles and molecules required for mitosis while in G2 • once G2 ends, mitosis begins!

When are growth factors important?

Growth Factors: important external regulators; they stimulate the growth and division of cells. important during embryonic development and wound healing.

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

Have the same number of chromosomes as each other and as the parent cell from which they were formed: • have the same genes as the parent cell and as each other • identical to each other, but smaller than parent cell

What are homologous chromosomes?

Homologous Chromosomes: Pair of chromosomes (maternal and paternal) that are similar in shape and size. Homologous pairs (tetrads) carry genes controlling the same inherited traits.

What happens at the G1 checkpoint if the cell gets a go-ahead signal? What if it does not?

If the cells receives a go-ahead signal, it usually completes the cell cycle and divides. If it does not receive a go-ahead signal, this cell exits the cycle and switches to a non-dividing state, the G0 phase. Most human cells are in this phase. Liver cells can be "called back" to the cell cycle by external cues (growth factors), but highly specialized nerve and skeletal/cardiac muscle cells never divide.

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

In eukaryotic chromosomes, DNA replication occurs at hundreds of places. Replication proceeds in both directions until each chromosome is completely copied.

Which chromosomes are autosomes? Which are sex chromosomes?

In humans, the autosomes are sets of 1-22. 23rd set of chromosomes = sex chromosomes.

Describe the DNA replication process in prokaryotes.

In prokaryotic cells, DNA is located in the cytoplasm. Most prokaryotes have a single, circular DNA molecule containing nearly all of the cells genetic information. In prokaryotes - replication begins at a single point and proceeds in two directions simultaneously until the DNA is copied. Prokaryotes (bacteria) have a single bubble. It is faster than DNA replication in eukaryotes.

What are internal regulations?

Internal Regulators: proteins that respond to events inside the cell, and allow the cell cycle to proceed only when certain processes have happened inside the cell. They stop cells at checkpoints in the cell cycle before moving to the next phase.

What jobs does DNA replication do? (hint: more than one!!)

It adds new DNA nucleotides, it removes primers, and it proof reads the DNA for errors.

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

Leading stands are synthesized continuously as one long strand from the point of origin toward the opening replication fork. Each individual lagging strand is synthesized against overall direction of replication, but all lagging strands as a whole can be said to be synthesized discontinuously, but over all toward the opening replication fork. They are made in different ways because DNA is anti-parallel, and new nucleotides can only be added to the 3' end, and the new strand must be made in the 5' —-> 3' direction.

What is a tumor?

Masses of cancer cells.

Metaphase - chromosomes line up in the "middle":

Metaphase only lasts for a few minutes. During metaphase: • The chromosomes line up across the center of the cell. • Microtubules connect the centromere of each chromosome to the spindle fibers.

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

Mitosis: PMAT Cell Cycle: IPMATC

What is anchorage dependence?

Most animal cells also exhibit anchorage dependence for cell division. • To divide, they must be anchored to a substratum (underlying layer or substance), typically the extracellular matrix of a tissue. Control appears to be carried out by connections between the extracellular matrix and plasma membrane proteins and cytoskeletal elements.

Why are new cells made?

New cells are produced for growth and to replace damaged or old cells (or in unicellular organisms, for reproduction).

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

Nuclease (exonuclease).

Mitosis is division of the ___?

Nucleus/ genetic material.

What are the lagging strand fragments called?

Okazaki fragments.

Do prokaryotes or eukaryotes perform DNA replication more rapidly?

Prokaryotes.

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

Telomeres are repeating segments of DNA located at both ends of a chromosome, and they make sure that all genes are replicated and not lost, and that the ends of chromosomes don't fray or stick to each other.

What is the M checkpoint for?

The M phase checkpoint ensures that all the chromosomes are properly attached to the spindle at the metaphase plate before anaphase. This ensures that daughter cells do not end up with missing or extra chromosomes.

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

The primer will be removed by DNA polymerase, and replaced with DNA nucleotides (by DNA polymerase) at the end of replication.

XX = ___? XY = ___?

XX = female. XY = male.