Cellular Reproduction: Cells from Cellscontents.kocw.net/KOCW/document/2014/hanyang/bertbinas/14.pdf · • Cells vs. organisms • Reproduction and proliferation • Non-sexual reproduction

CHAPTER 8

Cellular Reproduction: Cells from Cells

Chapter overview • Reproduction

• Cells vs. organisms

• Reproduction and proliferation

• Non-sexual reproduction

• Mitosis and the cell cycle

• Cancer

• Sexual reproduction

• Meiosis and sex

• Chromosomal abnormalities

• The advantages of diploidy and sex

Today • Reproduction

• Cells vs. organisms

• Reproduction and proliferation

• Non-sexual reproduction

• Mitosis and the cell cycle

• Cancer

• Sexual reproduction

• Meiosis and sex

• Chromosomal abnormalities

• The advantages of diploidy and sex

REPRODUCTION

• Is the creation of new organisms by organisms

• Can refer to single cells and multicellular organisms

• Can be asexual and sexual

• Asexual reproduction (reproduction from one parent) is based on “simple” cell division

Reproduction of Organisms

– Single cell organisms (example: amoeba)

– Some multi-cellular organisms – Lower animals (example:

hydra) – Plants can

• Sexual reproduction (reproduction from two parents) is based on a cycle of fertilization & reduction of chromosome number – More complex than asexual reproduction – Second half of this lecture plus next lecture

“SIMPLE” CELL DIVISION AND

THE CELL CYCLE

Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings

Cell division plays a role in

• The replacement of lost or damaged cells

• Wound healing

• Growth

• Reproduction

• Cancer

• Each minute, ~109 cells die in our body • Each day, ~1012 cells are formed in our body

Physical organization of genetic information

• The central event of cell division is the distribution of genetic information between daughter cells

• Cell division requires equal distribution of genetic information

• The complete set of all genetic information in an organism is called genome

• Human genome contains ~20,000 protein-encoding genes

• The genome is physically organized in pieces called chromosomes

This cell is dead, because it was killed by the staining procedure

Chromosomes


DNA double helix Histones

“Beads on a string”

Nucleosome

Tight helical fiber Supercoil

Sister chromatids

Centromere

2

1

3

4

The DNA is packed by coiling and folding: • 1st level: beads-on-a-string (nucleosome); each bead consists of DNA wound around a protein core of 8 histones • 2nd level: the beaded string is wrapped into a helical fiber • 3rd level: a thick supercoil. • 4th level: the supercoil is folded (this maximum folding only during cell division)

Structure of chromosomes

• Chromosomes are large continuous pieces of DNA in complex with packaging proteins (DNA + packaging proteins = chromatin)

• DNA in chromosomes is highly compacted

• Completely unfolded human chromosomes would be 16 – 85 mm long


Chromosomes may be small or large

The number of chromosomes does not inform about the amount of DNA

Number of chromosomes

• The cell cycle produces two daughter cells from a parent cell

• The central event of the cell cycle is the chromosome cycle

• A chromosome is the genetic information that is physically connected into one unit.

• 1 Chromosome consists of one chromatid or two chromatids (sister chromatids) that are connected at the centromere

• When the cell divides, the two sister chromatids separate from each other

Duplication

Sister chromatids

Cell cycle

1 chromosome = 1 chromatid

1 chromosome = 2 chromatids

1 chromosome = 1 chromatid

centromere

Cell division


•All eukaryotic cells that divide repeatedly undergo a cell cycle

•The cell cycle consists of two phases:

•Interphase

•Mitotic phase

Interphase (90% of time)

Mitotic phase (M)

(10% of time)


S phase

Interphase

Mitotic phase

G1 G2

Interphase

•The interphase consists of three parts:

•G1 (Gap 1): Cell growth

•S phase (DNA synthesis)

•G2 (Gap 2): Cell growth and preparation of mitotic phase


Mitosis and Cytokinesis

• Mitosis = division of nucleus

• Cytokinesis = division of the cytoplasm

• Mitosis and cytokinesis are different processes, but occur in a coordinated manner

• Cytokinesis starts in the final subphase of mitosis.

Interphase

Cytokinesis Mitosis


The four stages of mitosis

1.Prophase

• Condensation of the chromatin sister chromatids become visible in light microscope

• Centrosomes double, move apart, and produce spindle fibers (microtubules)

• Nuclear envelope dissolves Early mitotic spindle

Centrosome Centromere

Chromosome, consisting of two sister chromatids

Spindle microtubules

Fragments of nuclear envelope

Prophase


Metaphase

Spindle

Prophase 2. Metaphase

• Chromosomes convene on an imaginary plate equidistant from the two poles of the spindle

• The centromeres of all chromosomes are lined up at this plate.

• Spindle fibers from both poles attach to a centromere of each chromosome


3. Anaphase Anaphase

Daughter chromosomes

• Each chromatid is now an independent daughter chromosome.

• Motor proteins (= kinetochore) at the centromeres “walk” the daughter chromosomes along their microtubules toward opposite poles of the cell

• Meanwhile, these microtubules shorten

• The microtubules that are not attached to chromosomes lengthen, pushing the poles farther apart


4. Telophase

• Produces two daughter cells

• The reverse of prophase

• Nuclear envelopes form

• The chromosomes uncoil

• Nucleoli reappear

• Spindle disappears

Cleavage furrow

Nuclear envelope forming

Nucleolus forming

Telophase and Cytokinesis


Cytokinesis (= division of cytoplasm) • In animals, cytokinesis is caused by a ring of cytoskeletal proteins (microfilaments)

• In plants, membrane vesicles that contain cell wall material accumulate in the middle of the cell and gradually fuse

Cell wall

Vesicles containing cell wall material

Cell plate New cell wall

Cleavage furrow Contracting ring of microfilaments

Mitosis animations: http://www.maxanim.com/genetics/Mitosis/Mitosis.htm http://www.johnkyrk.com/mitosis.html Mitosis movies: http://www.youtube.com/watch?v=aDAw2Zg4IgE http://www.youtube.com/watch?v=DD3IQknCEdc


•This is actually not very precise: In the human body, 3x109 cells form every minute 30,000 errors occur each minute.


Normal plant and animal cells have a cell cycle control system that consists of special proteins

• These proteins generate “stop” and “go ahead” signals at certain key points during the cell cycle • The cell cycle normally halts at the G1 phase unless the cell receives a go-ahead signal • If that signal never arrives, the cell will switch into a permanently non-dividing state called G0

(for example, nerve and muscle cells) • If the go-ahead signal is received and the G1 checkpoint is passed, the cell will usually complete

the rest of cycle S phase

Interphase G1

Mitotic phase

(M)

G2

Go

G1 checkpoint

Muscle and nerve cells

•More than 500,000 people die of cancer in the USA each year •1/3 of all cancers in men are prostate cancer •¼ of all cancers in women are breast cancer

In Cancer Cells the Cell Cycle is Out of Control

Role

• Enables the continued existence of many species (single cells and multicellular organisms).

• Enables the maintenance and repair of organs.

• Loss of cell cycle regulation can lead to cancer.

Summary – Nonsexual reproduction Nature of nonsexual reproduction

• Creation of a new organism from a single parent, and the offspring is genetically identical to the parent.

Mechanism

• “Simple” cell division (mitosis). Repeatedly dividing cells go through cell cycles. Each cycle produces an exact copy of the genetic information of the parent cell.

Most important words to know

• Genome, chromosome, chromatid, chromatin

• Cell cycle, mitosis, interphase, cytokinesis

요약- 무성생식

무성생식의 특징

• 단일 부모로부터 새로운 유기체를 생산하며, 그 자손은 부모와 유전적으로 동일하다.

기작

• “단순한” 세포분열 (체세포분열, mitosis). 세포주기를 통해 반복적으로 세포가 분열함. 각 주기는 부모 세포의 유전정보를 정확하게 복사한다.

역할

• 많은 종 (단세포와 다세포 유기체)들의 존재를 지속시킨다.

• 장기의 유지와 보수를 가능하게 한다.

• 세포주기를 조절할 수 없는 세포는 암세포가 될 수 있다.

가장 중요한 단어들

• Genome, chromosome, chromatid, chromatin

• Cell cycle, mitosis, interphase, cytokinesis

SEXUAL REPRODUCTION AND MEIOSIS (Introduction)

– A new cell is created by “mixing” the chromosomes of two parent

cells number of chromosomes is doubled

– The cell with the doubled chromosome set can exist a long time and

even divide and create a multicellular organism

– Eventually, a special cell division reduces the chromosome number

back to the original level.

Sexual reproduction

– The mixing step that doubles chromosome number is called fertilization – The division that reduces the chromosome number is called meiosis. – Therefore sexual reproduction involves a cycle of fertilization & meiosis


• The human karyotype – 1 haploid set = 22 autosomes + X or Y – 1 diploid set = 22 pairs of autosomes + XX (♀) or XY (♂)

• The karyotype

– is the ordered set of chromosomes characteristic for each eukaryotic species

– The simple set of chromosomes (before fertilization) is called haploid

– The karyotype resulting from fertilization is diploid: The chromosomes exist in two copies

– The two copies are called homologous chromosomes

– The homologous chromosomes are almost identical: Same order of genes

The sexual life style is usually a cycle between a haploid and a diploid karyotype

http://en.wikipedia.org/wiki/Sex

Diploid stage (2n) of life cycle

Haploid stage (1n) of life cycle

In some organisms both the haploid (1n) and the diploid (2n) stages can multiply

http://en.wikipedia.org/wiki/Yeast

Life cycles of yeast

In multicellular organisms, either the haploid or the diploid stage dominates

1 n Main stage in lower plants (mosses)

2 n Main stage in •Higher plants (flowering plants) – only pollen and eggs are haploid; •Animals – only sperm and eggs are haploid

• In higher multicellular sexual organisms (higher plants and animals):

– Somatic cells do not transmit their genetic material to the next generation are mortal

(Somatic cells are diploid)

– Germ cells (egg, sperm) transmit their genetic material to the next generation are immortal

(Germ cells are haploid and generated by meiosis)

Multicellular sexual organisms have two principally different kinds of cells

In this chicken, the eggs and their precursors in the ovary

are the germ line cells - All other cells are somatic cells

• Hence, sex is the reason that we are mortal


Gametes and the life cycle of humans

Documents

Cellular Reproduction: Cells from Cellscontents.kocw.net/KOCW/document/2014/hanyang/bertbinas/14.pdf · • Cells vs. organisms • Reproduction and proliferation • Non-sexual reproduction