Biology

Cell Division

Chp 10 Mitosis

11 Meiosis

12 Genetics

There are different types of cell division for an important biological reason.

We have discussed the simplistic goals

of Life in 2 of the 3 categories of Acquire Energy in our previous chapters of Chemistry and Metabolism. (waste is in here)

The 3rd goal is to “Reproduce”.

Lets explore WHY this step so important to Biology?

Cell division by fission in Staphylococcus aureus, a disease-causing bacterium having resistance to multiple antibiotics.

Highlights of Chapter 10

Cell Division

Cell Cycle

Cancer and the Cell Cycle

Prokaryotic Cell Division

Remember: Cell Theory (Chp 4, “What is a Cell” lecture, slide 6)

What is Cell Division?

Divide as in to cleave into two. Make 2 out of 1.

This keeps with Cell Theory.

The process of Cell Theory is called the Cell Cycle

It comes in two types: Mitosis and Meiosis

Cell Cycle- an orderly sequence of events that describes the stages of a cell’s life from the division of a single parent cell to the production of two new daughter cells. The mechanisms involved in the cell cycle are highly regulated.

Why is here a “cycle” that is highly regulated or controlled?

Genome- is all the DNA of an organism. (we will go over what DNA is later).

Remember- DNA is a nucleic acid represents 1 of the 4 macromolecules of Life. Nucleic Acids are used to store information. DNA is a code.

DNA codes for EVERYTHING concerning the cell. It regulated Cell function including Division, so it must be copied for each new daughter cell.

Cell Cycle during division: We’ll take it in 4 steps.

Remember- Goal is to make 2 cells from 1.

G1 phase- The cell grows. “g”-grow.

S phase- copy genome (DNA). “s”-synthesis of DNA

G2 phase- the cells “recovers” (rests), grows, copying organelles, dismantling cytoskeleton

Mitosis- “all Copies done” & energy ready = Nucleus & cell divide

Mitosis- the dividing of a cell and its genome. In a eukaryote that included the nucleus and all organelles.

Fig 10.5

THM- of Cell Division

Eukaryotic cells alternate in a cycle between cell division and other cell activities. Living or dividing.

The cell division portion of the cycle is called the mitotic phase.

The remainder of the cell cycle, called interphase, consists of two gap phases (during which cell growth and other metabolic activities occur) separated by a DNA synthesis phase, S phase, during which the genetic material is replicated.

Once ALL DNA is replicated… a cell divides.

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There is a time for everything in the eukaryotic cell cycle.

The alternation of activities between cell division and other processes is called the cell cycle.

 

The cell cycle describes the series of phases that leads to cell division.

These phases are divided into a cell division phase, called mitosis, and a phase of growth and non-reproductive activities, called interphase.

Because interphase is further subdivided, four distinct phases of the cycle are recognized.

A eukaryotic cell moves through the phases in this order and is always somewhere within this cycle.

The phases are: mitosis and the three phases of interphase—Gap 1, DNA synthesis, and Gap 2.

 

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Cancer and the Cell Cycle: 10.4

What is cancer? Cancer is “uncontrolled” cell growth.

Looking at Mitosis- when a cell divides, Genome must duplicate a copy for each new daughter cell.

This process is called replication. IF an error occurs in the code this is a mutation. If the error is in the code to control Mitosis, then “division is uncontrolled”.

There are genes (code) called tumor suppressor genes that regulate an replication errors.

This is why Mitosis is highly regulated cell cycle.

But why do EUKARYOTIC cells divide?

* Why are there two process for cell division? Mitosis and Meiosis

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Life’s 3 Goals: 1. Consume Energy. 2. Get rid of waste. 3 Reproduce

Two different kinds of cell categories:

MITOSIS – * Somatic cells: Any cell forming the body of an organism (goals 1&2)

Meiosis – * Germ cell: Any cell that gives rise to the gametes of an organism that reproduces sexually. (goal 3)

The organization and distribution (heredity) of the DNA is different.

Mitosis and Meiosis solve these requirements.

Basically… Cells (*multicellular organisms) need to grow and replace themselves

1. Growth. During growth and development, organisms get bigger and must add new cells. In fact, if you want to see cell division in action, one sure-fire place to look is at the tip of a plant root because that is one of the fastest growing parts of a plant, at about half an inch per day (Figure 6-7 Part 1 Reasons for mitosis).

2. Replacement. Cells also must be replaced when they die. The wear and tear that comes from living can physically damage cells. The daily act of shaving, for example, damages thousands of cells on a man’s face (Figure 6-7 Part 2 Reasons for mitosis). It’s nothing to worry about, though. Microscopic views of human skin reveal several distinct layers, with the outermost layers—the layers under assault during shaving—made up primarily from dead cells. These cells help protect us from infection and also reduce the rate at which the underlying living cells dry out. The living cells that exist just below the layers of dead cells are being produced at a high rate by mitosis; they can also be harmed if you’re not careful.

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Prokaryotic Cell Division- That “other cell” from Chapter 4.

Mitosis and next Meiosis are how Eukaryotes divide, but there is more than one kind of cell on Earth.

Prokaryotes undergo a cellular process called binary fission. This is the usual form of asexual replication for bacteria. Prokaryotes are less complicated organisms, thus it is a simple identical copy.

Single celled Eukaryotes that “copy themselves” still undergo Mitosis, which is still a process of making an identical copy.

Copy the DNA: Genomes are circular or linear.

Eukaryotes have much more DNA.

In eukaryotes, genetic information is organized into linear chromosomes.

Eukaryotic chromosomes float freely in the nucleus.

As a method for storing genetic information, DNA has complete market saturation. All life on earth uses it. This is pretty remarkable considering the tremendous diversity of life that exists on earth—from bacteria to plants and animals. One way in which different organisms’ DNA varies is in how it is organized into chromosomes.

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Highlights of Chapter 11 Meiosis and Sexual Reproduction.

Process of Meiosis

Sexual Reproduction

As mentioned in Chp 4 & 5: all cells come from preexisting cells (Cell Theory), an egg is a “single cell”, but how and why does a multicellular organism made of trillions of cells start from a single cell?

What about the DNA?

Why are there two forms of cellular division?

Remember: Two different kinds of cell divisions for eukaryotes.

There are two versions because of sex.

Let’s use humans as our eukaryotic example. We are mammals and a eukaryote.

Of the trillions of cells in you most tissues and organs use Mitosis to grow and repair you. They are copies of copies… etc

Your sexual organs have secialized Germ Cells to form eggs and sperm. Egg and sperm are called haploid cells. Haploid cells have half the DNA of the parent.

Sex has the goal of joining the DNA (1/2 mom) in an egg (oocyte) and the DNA (1/2 Dad) in one sperm to make a new (1:whole) cell (zygote) that will grow mitoticly into a new human of another trillion cells. The secret is that this new individual is not an exact copy of the parents.

MITOSIS – * Somatic cells: Any cell forming the body of an organism (goals 1&2)

Meiosis – * Germ cell: Any cell that gives rise to the gametes of an organism that reproduces sexually. (goal 3)

The organization and distribution (heredity) of the DNA is different.

Mitosis and Meiosis solve these requirements.

What is Meiosis?

Meiosis- is nuclear division that forms haploid cells.

Mitosis occurs almost everywhere in an animal’s body. Meiosis only occurs in one place.

Where?

What’s the “goal” of this other form of cell duplication?

Hint: It’s not directly

about the “cell”

A simple look at Meiosis

Figure 6-19 (not in your book) Meiosis reduces the genome by half in anticipation of combining it with another genome.

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Meiosis is more complicated. It has to essentially ”double” the steps of Mitosis.

I prefer the simpler version for our needs of this class. DON’T get lost in memorizing all the steps… That’s for biology majors.

Why not learn the steps of Meiosis now?

Know WHY Meiosis happens.

Know the difference

between

Mitosis and

Meiosis

Notice!

Look at “outcome”

Know the difference between Mitosis and Meiosis-

Diploid cells with full genomes undergo Mitosis, and

special diploid germ cells undergo Meiosis to make

haploid cells.

Fig 11.8

Know why Meiosis happens- Sex. To make an offspring

with genetic variation to the parents original DNA.

Our bodies have a problem to solve relating to cell division. We are sexually reproducing organisms; that is, when offspring are created, they carry the genetic material from two individuals. But think about the difficulties this presents. If reproductive cells were produced through mitosis, both parents would contribute a full set of genes—that is, 23 pairs of chromosomes in humans—to create a new individual; the new offspring would inherit 46 pairs of chromosomes in all. And when that individual reproduced, if she contributed 46 pairs of chromosomes and her mate also contributed 46 pairs, their offspring would have 92 pairs of chromosomes. Where would it end? The genome would double in size every generation. That wouldn’t work at all. At the very least, within a few generations cells would be so overloaded with chromosomes that they would explode.

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Know why Meiosis happens- Sex. The evolution of sex is important because it increases the chance to produce better offspring as a result of the genetic variation created by Meiosis. Meiosis performs genetic recombination called a “crossover”.

What? Sex!

Two parents do not make an identical child every time. Each offspring is a “little different” mix of the parents. (excluding genetic twins)

During a step of Meiosis the chromosomes swap DNA. This occurs in the mom and dad. Thus a each creation of an egg produces a different egg.

Same with sperm

Crossover occurs between non-sister chromatids of homologous chromosomes. The result is an exchange of genetic material between homologous chromosomes.

Occurs when making 1 egg in mother. This mother get her DNA from her Dad and Mom.

DNA (blue-Dad) (Red-Mom)

Egg #1

Egg #2  into

X

= Genetic mix?

Sex!

sperm

What are the costs and benefits of sexual reproduction?

Sexual reproduction leads to offspring that are all genetically different from each other and from either parent in three different ways (Meiosis + fertilization)

Asexual Reproduction (Mitosis & Binary fission) is fast! Some bacteria split every 20 min/generation. But all “new” generations are the “same” (mutations?)

Sexual reproduction takes 2.

At costs of…

At great benefits of…

There are fundamentally different ways that cells and organisms can reproduce. On one hand there is mitosis and asexual reproduction via binary fission. On the other hand, there is meiosis and sexual reproduction. Is one method better than the other? It depends. In fact, the more appropriate question is: what are the advantages and disadvantages of each and under what conditions do the benefits outweigh the costs?

Crossing over and meiosis: creating many different combinations of alleles.

Crossover can occur during the creation of haploid cells within one parent and then again during fertilization and the combining of the egg/sperm during the first mitosis event. It will occur again when that new individual Germ Cells undergo Meiosis to produce egg or sperm.

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Why is “sex” a big deal?

Life cycles of organisms from single to multicellular that preform sex have evolved a way to make consecutive generations that have the “chance to be an improvement” from the previous generations to face the uncertain future.

Read “The Red queen Hypothesis” in your book. 11.2, page 313.

This genetic variation created during EVERY generation between EVERY member of a species is a major concept in the process of Evolution by Natural Selection.

This genetic variation is also why a curious Scientist named J. Gregor Mendel set to work on the biological process of inheritance… or also called Genetics. Chapter 12

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Meiosis

Gametes- a cell that will combine at fertilization (sexual reproduction) to produce offspring. A reproductive cell.

Diploid- refers to cells that have two copies of each chromosome (in humans that is two sets of 23= 46)

Haploid- refers to cells that have one copy of each chromosome. 23 (Germs cells= gametes)

* haploid gametes maintain a stable genome size in a species and allow for different combinations to be passed to the next generation (inherited).

Sexually reproducing organisms have evolved a way to avoid the inevitable chromosome overload. It is called meiosis, a process that enables organisms, prior to fertilization, to make special reproductive cells called gametes that have only half as many chromosomes as the rest of the cells in the body. In other words, in anticipation of combining one individual’s genome with another’s, meiosis reduces each individual’s genome by half. In humans, for example, gamete cells have only one set of 23 chromosomes, rather than two sets.

In studying genetics, the term diploid refers to cells that have two copies of each chromosome, and the term haploid refers to cells that have one copy of each chromosome. Thus, somatic cells are diploid and gametes, the cells produced in meiosis, are haploid.

At reproduction, two haploid cells, each with one set of 23 chromosomes, are brought together creating a new individual with the proper diploid genome of 46 chromosomes. And when the time comes to reproduce, this new individual also will produce haploid gametes through meiosis that have only a single set of 23 chromosomes. With sexual reproduction, then, diploid organisms produce haploid gametes that fuse at fertilization to restore the diploid state. This repeats perpetually and maintains a stable genome size in a species.

There are some variations on this pattern of alternation between the haploid and diploid state. Most multicellular animals, nonetheless, produce simple haploid cells for reproduction. And after two of those gametes come together as a diploid fertilized egg, multiple cell divisions via mitosis produce a diploid multicellular animal again.

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Highlights of Chapter 12 Mendel’s Experiments and Heredity

Chapter 12

Laws of Probability

Characteristics and traits

Laws of Inheritance

Johann Gregor Mendel is considered the father of genetics.

We will explore this as it was discovered with larger perspective of organism to chromosomes to DNA, based on advancements of technology. What was able to be observed? ”Size” is important to the progression of these discoveries.

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Genetics is the study of heredity.

Heredity is the result of sexual reproduction.

Sexual reproduction has the goal of genetic variance.

… but how did Science begin to understand what genetic variance is?

Now… “The Science” and “the maths” of these principles in biology need to be discussed.

The class is taught in a particular order of facts, concepts, information becuase we NOW know how Life works, but in the beginning it took individuals with keen Scientific minds to make observations of biological phenomenon that provided emperical data (facts) to change how we think.

G. Mendel and his work is nicely described here Chapter 12.1, page 322-3, but he used the core principles of the Scientific Method, a good organism, and time, to collect repeatible data and thus emperical data for “variation” found in Life.

Understanding “variation” of heredity then suports Darwin’s Evolution by Natural Selection.

In Mendel’s experiements, he “removed” the natural processes for systimatic controlled cross breading to understand ”traits” and generational mixing of traits called “hybridization”.

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Vocab to Inheritance-

Generation- the offspring of crossing to distinct genotypes or “parents: PO”. F1 generation is the first set of offspring from the original pairing PO, The F2 generation is the offspring of parental F1 crossing. And so on…

Continuous variation: The original concept in biology before Mendel’s work. A gene determines a trait and genes of parents are “blended” to explain variation and parents traits were “lost” in future generations as they were mixed “to be” the offspring.

This had some observable inconsistences and Mendel sought to figure it out.

Discontinuous variation: traits being inherited in “distinct classes”, such as color or shape, that can be passed on “whole”.

He noticed that there was a mathimatical probobility to his generations and that some “traits” skipped generations and where not “lost”, but somehow were inherited but skipped being observed.

To explore this Mendel created, found, used plants with distinct single traits. “Color”: example ALL generations produced purple flowers or ALL generations produced white flowers.

He then crossed KNOWN PO parents purple and white to create a Hybridization- two indiv with clear seperate inheritale traits crossed to produce varried offspring.

What’s a Trait? Is defined as a variation in physical apperance of a heritable characteristic.

After a reported 19,959 F2 crosses his notice of ratios proved correct. But for every cross his numbers had ratios of 3:1 puple:white, or 75% purple to 25% white. Which led him to concluded that some traits were-

inherited and unchanged in hybridization, to be defined as a Dominant trait.

– Inherited and latent, disappear for generation(s) in hybridization, thus the offspring “change” in appearance, to be defined as a Recessive trait.

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