Cell ReproductionCell Reproduction

Chapter 4 NotesChapter 4 Notes

Why is cell division important?Why is cell division important?

Many celled organisms grow because cell Many celled organisms grow because cell division increases the number of cells they division increases the number of cells they have. have.

One-celled organisms reproduce using cell One-celled organisms reproduce using cell division.division.

The Cell CycleThe Cell Cycle

Like organisms have life cycles, cells have life Like organisms have life cycles, cells have life cycles. cycles.

It is a series of events that takes place from one It is a series of events that takes place from one cell division to the next.cell division to the next.

The time it takes to complete the cycle is not the The time it takes to complete the cycle is not the same for all organisms or all cells in an same for all organisms or all cells in an organism. organism.

Most of the time, a cell is in interphase. Most of the time, a cell is in interphase. (Inter=between) (Between cell divisions). It is a (Inter=between) (Between cell divisions). It is a period of growth and development. After that, period of growth and development. After that, cell division begins.cell division begins.

Study Figure 2 on page 97.Study Figure 2 on page 97.

MitosisMitosis

PART of cell division—the PART of cell division—the nucleus divides into twonucleus divides into two. . The The two new nuclei will be identicaltwo new nuclei will be identical because everything because everything

duplicates (copies) before it separates (during duplicates (copies) before it separates (during interphase). The chromosomes thicken into coils called interphase). The chromosomes thicken into coils called chromatids and they attach to their pair at a spot called chromatids and they attach to their pair at a spot called a centromere.a centromere.

Steps of mitosis: (PMAT)Steps of mitosis: (PMAT) prophase – nuclear membrane breaks down, chromatid pairs prophase – nuclear membrane breaks down, chromatid pairs

are visible, centrioles move to opposite ends of the cellare visible, centrioles move to opposite ends of the cell metaphase – the pairs of chromatids line up at the center of the metaphase – the pairs of chromatids line up at the center of the

cell, centromere is attached to centriole by spindle fiberscell, centromere is attached to centriole by spindle fibers anaphase – centromere divides, spindle fibers shorten and anaphase – centromere divides, spindle fibers shorten and

chromatids begin to move to opposite ends of the cell (now they chromatids begin to move to opposite ends of the cell (now they are called chromosomes again)are called chromosomes again)

telophase – new nucleus forms, chromosomes uncoiltelophase – new nucleus forms, chromosomes uncoil

Cell DivisionCell Division

After mitosis, the cytoplasm divides and After mitosis, the cytoplasm divides and two new cells are created.two new cells are created.

In animal cells, the cytoplasm pinches in In animal cells, the cytoplasm pinches in (like a balloon with a string tied around it).(like a balloon with a string tied around it).

In plant cells, a cell plate forms and new In plant cells, a cell plate forms and new cell walls grow on each side. cell walls grow on each side.

After the cytoplasm divides, the cell enters After the cytoplasm divides, the cell enters interphase again, the period of growth and interphase again, the period of growth and development.development.

Asexual ReproductionAsexual Reproduction

Some organisms with eukaryotic cells can Some organisms with eukaryotic cells can reproduce asexually by using cell division. reproduce asexually by using cell division. All cells will be genetically identical to the parent cell All cells will be genetically identical to the parent cell

because of the duplication of the nucleus that because of the duplication of the nucleus that happens in mitosis.happens in mitosis.

Bacteria do not have a nucleus, so they can’t Bacteria do not have a nucleus, so they can’t use mitosis/cell division to reproduce asexually. use mitosis/cell division to reproduce asexually. They use fission.They use fission.

Budding – new organism growing from the body Budding – new organism growing from the body of a parent organismof a parent organism

Regeneration – process that uses cell division to Regeneration – process that uses cell division to replace lost body partsreplace lost body parts

Body Cells vs. Sex CellsBody Cells vs. Sex Cells

Two types of cells in your body—body Two types of cells in your body—body cells and sex cells. (ALL cells except sex cells and sex cells. (ALL cells except sex cells (sperm and egg) are body cells.)cells (sperm and egg) are body cells.)

Body cells – chromosomes are in pairs Body cells – chromosomes are in pairs (diploid). Humans have 23 pairs (46 (diploid). Humans have 23 pairs (46 chromosomes).chromosomes).

Sex cells – have half the number of Sex cells – have half the number of chromosomes as body cells (one from chromosomes as body cells (one from each pair). (23 for humans.) each pair). (23 for humans.)

Sexual ReproductionSexual Reproduction

Two sex cells come together—sperm Two sex cells come together—sperm (male) and egg (female).(male) and egg (female).

The sperm cell enters the egg cell in a The sperm cell enters the egg cell in a process called fertilization.process called fertilization.

The resulting cell is called a zygote.The resulting cell is called a zygote.

MeiosisMeiosis

Meiosis is the process used to create haploid Meiosis is the process used to create haploid cells so that sexual reproduction can take place.cells so that sexual reproduction can take place. Sex cells have half so that when they combine with Sex cells have half so that when they combine with

another sex cell, which also has half, the result will be another sex cell, which also has half, the result will be “whole.” [If two diploid cells combined, the offspring “whole.” [If two diploid cells combined, the offspring would have double the amount of chromosomes.]would have double the amount of chromosomes.]

During meiosis, the nucleus divides twice During meiosis, the nucleus divides twice (Meiosis I and Meiosis II).(Meiosis I and Meiosis II).

Study diagrams and descriptions on pages 106-Study diagrams and descriptions on pages 106-107.107.

DNA (deoxyribonucleic acid)DNA (deoxyribonucleic acid)

Contains information that an organism needs to Contains information that an organism needs to grow and functiongrow and function

Has a structure that resembles a twisted ladderHas a structure that resembles a twisted ladder sides are made up of sugar-phosphate moleculessides are made up of sugar-phosphate molecules rungs are made up of nitrogen bases (remember this rungs are made up of nitrogen bases (remember this

later for nitrogen cycle)later for nitrogen cycle)

To duplicate itself, it unwinds, separates its To duplicate itself, it unwinds, separates its sides, and then forms new sides.sides, and then forms new sides.

GenesGenes GenesGenes—sections of DNA on a chromosome —sections of DNA on a chromosome

(pieces of code) [Ex: like a slice is part of a loaf](pieces of code) [Ex: like a slice is part of a loaf] Contain instructions for making specific proteinsContain instructions for making specific proteins RNA carries codes for making proteins from the RNA carries codes for making proteins from the

nucleus to the ribosomes in the cytoplasmnucleus to the ribosomes in the cytoplasm Messenger RNA (mRNA), Ribosomal RNA (rRNA), Messenger RNA (mRNA), Ribosomal RNA (rRNA),

Transfer RNA (tRNA)Transfer RNA (tRNA) Cells use only the genes that direct the making Cells use only the genes that direct the making

of proteins needed by that cell (like a character of proteins needed by that cell (like a character in a play only reads the lines in the script for in a play only reads the lines in the script for them)them)

MutationsMutations

Any permanent change in the DNA Any permanent change in the DNA sequence of a cell’s gene or chromosome. sequence of a cell’s gene or chromosome. can change the traits of the organismcan change the traits of the organism can be caused by outside factors like X-rays, can be caused by outside factors like X-rays,

sunlight, and some chemicalssunlight, and some chemicals Can be passed to offspring only if mutation Can be passed to offspring only if mutation

is passed to a sperm or egg cell.is passed to a sperm or egg cell.