Cell Reproduction

Disclaimer:Please remember that none of the information provided is in any way an encouragement for students to “investigate” on their ownAll “experiments” must be approved by: teacher, parents/guardians, and a possible religious leader of your choiceThank you and enjoy the show

Structure of a Chromosome

Structure (cont.)

Rod-shaped made of DNA wrapped around proteins In Prokaryotes, DNA is circular and have

associated proteins In Eukaryotes, the proteins are histones

Maintain shape Aid in tight packing of DNA

Nonhistone proteins Involved in controlling activities of specific regions

of DNA

Structure (cont.)

Made of two chromatids attached at the centromere

These form as DNA copies itself

Chromatin

Between cell divisions, DNA loosens up and (under a microscope in most situations) chromatin forms

Easier to read Information can be used to direct cells

activities

Chromosome NumbersA human adult – 40+ Sex chromosomes are 2

of the 46 -determine the sex of the offspring-carry genes for other characteristics-humans are X or Y

Autosomes

All other chromosomes Every cell of organism produced by sexual

reproduction Autosome from mother + Autosome from

father = Homologous chromosome Carry genes for same trait Same size and shape

46 Human Chromosomes

22 Homologous Pairs of Autosomes 2 Sex Chromosomes

Diploid vs. Haploid Cell

Diploid- 2 sets of chromosomes All normal cells except

reproductive 2n

Haploid – 1 set of chromosomes Sperm/Egg 1n

Diploid

Haploid

Cell Cycle

Interphase – precedes mitosis DNA duplicates Nucleolus may be

visible in this phase, however, the chromosomes are not visible

Cell is involved in metabolic activity

Nucleolus

How do you knowthis is a plant cell?

Nuclear membrane

CellWall

Prophase

This stage is the first stage of cell division Chromosomes become more visible Chromatin fibers are thick enough to be seen

with a light microscope. Sister chromatids joined at the centromere

can be seen under high power. Late in this phase the nuclear envelope

breaks down (looks like dashes) Mitotic spindle (made from microtubles) forms

in the cytoplasm – chromatids attach to microtubles; spindle is football shaped; spindle tugs chromosomes towards middle of cell.

Cell wall

NuclearEnvelope – Begins breakingdown

Metaphase

This stage is very brief Chromosomes gather in the Middle Mitotic spindle is completely formed

and all chromosomes are attached to these microtubules

Centromeres are lined up about halfway between the two poles

Mitotic Spindle

Chromosomes are lined up in center

Poles

Anaphase

This is the third stage Sister chromatids suddenly separate

and are now considered “daughter” chromosomes

Microtubules shorten, pulling the chromosomes closer to the poles

Spindle microtubules that are not attached to the centromeres grow longer and push the poles farther apart.

Poles

“Daughter”chromosomespulled towardspoles

Spindle attachedto chromosomes

Spindle elongatesand stretches polesapart

Telophase and Cytokinesis

This is the final stage of mitosis Chromosomes reach the poles of the

spindle Spindle disappears Two nuclear envelopes form around each

new daughter chromosome Chromosomes uncoil and lengthen Nucleoli reappear Cytokinesis divides the cytoplasm into two

daughter cells, each with a new nucleus – this usually occurs along with telophase

Cytokinesis separates thecytoplasm

Interphase

This stage starts the whole cycle over again.

MeiosisCell division in eukaryotes

Meiosis vs. Mitosis

Yet another comparison…

Meiosis Outcome

The products of meiosis are 4 Haploid daughter cells: Sperm cells Egg cell and polar bodies

Meiosis I and Meiosis II

What are the main differences between Meiosis I and Meiosis II? Look at what is going on inside Write in your notes what is happening….

Cell Division in Prokaryotes

Binary Fission -