The Cell Cycle Life cycle of cells Begins

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The Cell Cycle ©Life cycle of cells ©Begins with cell formation ©Ends when the

The Cell Cycle ©Life cycle of cells ©Begins with cell formation ©Ends when the cell divides & forms new cells

Why Cells Divide © Growth © Repair & Replace (maintain) © Reproduce © Mitosis

Why Cells Divide © Growth © Repair & Replace (maintain) © Reproduce © Mitosis (asexual = makes clones) like binary fission of bacteria © Meiosis (forms gametes for sexual reproduction)

Cell Size Limitations • The cells that make up a multicellular organism come in

Cell Size Limitations • The cells that make up a multicellular organism come in a wide variety of sizes & shapes. • Considering this wide range of cell sizes, why then can’t most organisms be just one giant cell? Diffusion limits cell size • Although diffusion is a fast & efficient process over short distances, it becomes slow & inefficient as the distances become larger. • Because of the slow rate of diffusion, organisms can’t be just one giant-sized cell.

Surface area-to-volume ratio If cell size doubled in size, the cell volume would require

Surface area-to-volume ratio If cell size doubled in size, the cell volume would require 8 times more nutrients & would have 8 times more waste to excrete. 4 mm 1 mm 2 mm 1 mm mm 2 Surface area = 6 Volume = 1 mm 3 4 mm 2 mm 4 mm Surface area = 24 mm 2 Volume = 8 mm 3 The surface area, however, would increase by a factor of only 4. The cell would either starve to death or be poisoned from the buildup of waste products.

Eukaryotic Reproduction: • Before eukaryotic cell division, DNA (chromatin) coils tightly around proteins &

Eukaryotic Reproduction: • Before eukaryotic cell division, DNA (chromatin) coils tightly around proteins & forms chromosomes. • At cell division, each chromosome consists of 2 sister chromatids attached at the centromere. • The chromatids separate during cell division into each new cell.

CHROMOSOMES Sister Chromatids are the two Parts of the chromosome and Are connected by

CHROMOSOMES Sister Chromatids are the two Parts of the chromosome and Are connected by the centromere

Chromosomes • Sets of Chromosomes • Each organism has a characteristic number of chromosomes.

Chromosomes • Sets of Chromosomes • Each organism has a characteristic number of chromosomes. • Human somatic (body) cells are diploid (2 N) with 23 pairs (46 in total) of homologous chromosomes – contain genes that code for the same traits • Human gametes are haploid (N), with 23 chromosomes. Gametes are sex cells (sperm and egg) used in sexual reproduction • Sex Chromosomes- the 23 rd pair • These carry information that determines an organism’s sex. XX= female. XY= male

This is the cell cycle Interphase (most of the time) Consists of G 1,

This is the cell cycle Interphase (most of the time) Consists of G 1, G 0, S and G 2 Interphase is sometimes known as the resting phase, but it is also when DNA is replicated by the cell (in the S phase) Study this!!! Mitosis: replicated chromosomes are split into two new daughter cells. See your notes and the workshops to learn about the phases of mitosis: Prophase, Metaphase, Anaphase and Telophase. Cytokinesis: the division of one cell into two daughter cells When cancer happens, the cell can’t reach G 0, it repeats the process of replication and division over and over. G 0: the cell stops dividing

The Cell Cycle Eukaryotic Cell • Interphase: A cell spends 90% of its time

The Cell Cycle Eukaryotic Cell • Interphase: A cell spends 90% of its time in interphase Interphase consists of 4 phases • G 1 - Growth • G 0 - Division stops • S - DNA synthesis-replication • G 2 - Preparation for cell division • Mitosis- division of the nucleus (chromosomes) • Cytokinesis- division of the cytoplasm S G 1 G 2

Before cell division: ©DNA replicates ©Remember, DNA has info that tells a cell how

Before cell division: ©DNA replicates ©Remember, DNA has info that tells a cell how to make proteins

DNA Replication happens in the S phase G 0

DNA Replication happens in the S phase G 0

Now we will look at the steps of DNA replication. Pay attention to the

Now we will look at the steps of DNA replication. Pay attention to the order and the enzymes involved.

Step 1 An enzyme called helicase “unzips” the DNA by breaking the hydrogen bonds

Step 1 An enzyme called helicase “unzips” the DNA by breaking the hydrogen bonds apart and creating a replication fork. Each strand from the original molecule of DNA is called the “parent” strand.

Step 2 Enzymes called DNA polymerases add nucleotides one at a time to each

Step 2 Enzymes called DNA polymerases add nucleotides one at a time to each parent strand. Each new strand is called a “daughter” strand

Step 3 The enzyme DNA ligase joins the backbone of each nucleotide together What

Step 3 The enzyme DNA ligase joins the backbone of each nucleotide together What is the backbone of DNA made of?

©With a partner, see how many of these questions you can answer… ©Helicase and

©With a partner, see how many of these questions you can answer… ©Helicase and polymerase are what kind of biomolecule? ©What does DNA Polymerase do? ©What does helicase do? ©What does ligase do? © 5’ to 3’ and 3’ to 5’ means that DNA replication is anti-_____.

The Ameoba Sisters ©https: //www. youtube. com/watch? v=5 q. Srmei. Ws uc#action=share

The Ameoba Sisters ©https: //www. youtube. com/watch? v=5 q. Srmei. Ws uc#action=share