Lecture 13: The Cell Cycle

Question 1

What is heredity?

Answer 1

-All organisms come from other organisms
-All organisms resemble their parents
-Siblings are not identical

Question 2

Why do children look like their parents?

Answer 2

Sperm and eggs are single cells that fuse together to become a zygote.
-This explains why you get features from both parents

Question 3

How are organism made from one diploid cell?

Answer 3

Diploid cells divide many times to produce an organism(organisms are multicellular)

Question 4

True or False: Every cell in your body derives from one single cell?

Answer 4

TRUE

Question 5

What do daughter cells need to inherit from mother cells?

Answer 5

Daughter cells must inherit everything from the mother cells that they need to be successful

Question 6

What is one very important thing that all daughter cells need?

Answer 6

Mitochondria

Question 7

Cells contain multiple mitochondria, if a daughter cell only get one mitochondria from the mother cell how can it eventually get more?

Answer 7

Mitochondria can also divide

Question 8

What are chromosomes?

Answer 8

-A package made up of one single double stranded DNA molecule

Question 9

What are the two types of chromosomes?

Answer 9

Circular chromosome: Found in bacteria which have circular DNA
Linear Chromosome: Found in eukaryotes

Question 10

Why are we able to see chromosomes under a microscope?

Answer 10

-When a cell is getting ready to divide the chromosomes condense by associating with proteins such as the histone protein
-That is what can be seen

Question 11

What are the proteins that help chromosomes condense before dividing ?

Answer 11

Histones

Question 12

So what is seen under a microscope when chromosomes are condensed?

Answer 12

DNA wrapped up in a tight knot around the histone proteins

Question 13

What is a karyotype?

Answer 13

A way of organizing and identifying chromosomes

Question 14

How to make a karyotype(DIY!)?

Answer 14

1.Take a cell in its process of dividing and put a cover slip on top of it and flatten it(mitotic squash)
2.This causes the cell to break open and the chromosomes spread out everywhere
3.The chromosomes are then stained and a photo of them is taken
4. Then line the chromosomes up into a pattern that you see

Question 15

What does the karyotype reveal about chromosomes?

Answer 15

They come in pairs

Question 16

What are pairs of chromosomes called?

Answer 16

Homologs

Question 17

How many chromosomes do humans have?

Answer 17

23 pairs chromosomes(homologs), 46 individual chromosomes

Question 18

What two chromosomes don’t appear to have pairs?

Answer 18

X and Y

Question 19

True or False: The number of chromosomes depends on the organism/species?

Answer 19

TRUE

Question 20

What happens to chromosomes right before division?

Answer 20

Each chromosome is replicated to produce two chromatids attached by a centromere

Question 21

What is found in each chromatid?

Answer 21

Each chromatid has one double-stranded piece of DNA

Question 22

After chromatids are formed, how many strands of DNA are found in each pair of homologous chromosomes?

Answer 22

4 strands of double stranded DNA
1 per chromatid, 4 chromatids

Question 23

What is a mitotic chromosome?

Answer 23

Chromatids two identical pieces of DNA bound by a centromere
-It is called this because it is about to undergo division and must have two strands of DNA

Question 24

What is a sister chromatid?

Answer 24

-Identical chromatids with duplicated genetic material
-There are two sister chromatids in a mitotic chromosome

Question 25

How many chromosomes do daughter cells need?

Answer 25

Each daughter cell NEEDS one of each chromosome because they carry essential genetic material

Question 26

Can daughters receive more than one of each chromosome?

Answer 26

No they cannot as this can cause problems such as Down syndrome

Question 27

What extra chromosome causes down syndrome?

Answer 27

people with down syndrome have an extra chromosome 21

Question 28

How do cells ensure that daughter cells receive only one of each chromosome and no more?

Answer 28

Make sure the chromosome is duplicated once before the cell divides

Question 29

What is the first stage of cell division?

Answer 29

S phase - Chromosome DNA replication

Question 30

What is the second stage of cell division?

Answer 30

Mitosis or Meiosis

Question 31

What is mitosis?

Answer 31

Somatic cells make identical clones of themselves by creating daughter cells that inherit one chromosome

Question 32

What is meiosis?

Answer 32

Process by which germ cells(reproductive cells) make non-identical copies of themselves by creating daughter cells that have one of each homolog

Question 33

What is the third stage of cell division?

Answer 33

Cytokinesis: dividing the cytoplasm in two(optional)

Question 34

What are the four stages of the cell cycle?

Answer 34

1. Gap phase 2. DNA Synthesis 3. Gap 2 4. Mitosis

Question 35

What happens during the gap phase of the cell cycle?

Answer 35

-Cell grows -Builds up mitochondria and ribosomes so that it can later give them to its daughter cells

Question 36

What happens during DNA Synthesis of the cell cycle?

Answer 36

Creation of one and only one copy of the DNA

Question 37

What happens during the gap 2 phase of the cell cycle?

Answer 37

Verification that DNA is properly ready and cell is ready for division

Question 38

What happens during the mitosis stage of the cell cycle?

Answer 38

Chromosomes divide and cell splits in two daughter cells

Question 39

How does the cell regulate the cell cycle?

Answer 39

-Cell has checkpoints to make sure the cell is ready to enter the next phase

Question 40

What proof is there to prove that these checkpoints exist?

Answer 40

First, scientists added drugs into the chromosomes to ensure that the cell could not efficiently replicate the DNA. What they saw was that the cell stopped before it could undergo cell division Then, scientist disabled the check point by adding caffeine then added the drug to stop replication and what they saw was the cell continued to undergo cell division

Question 41

What are the check points?

Answer 41

The check points are proteins that make sure everything is ready to move to the next phase -CDK and Cyclins

Question 42

What proteins are important for the transition from G1 to S phase?

Answer 42

-Cyclin A -CDK2

Question 43

True or False: Little effort is used by cells to make sure each daughter cell inherits equally

Answer 43

True and False, simply making sure the division occurs roughly in the middle of the cell seems to do the trick. However, cells do spend a lot of time dividing up their chromosomes

Question 44

Why are karyotypes made with dividing chromosomes?

Answer 44

Only during division chromosomes are visible

Question 45

What is the karyotype made of?

Answer 45

Mitotic Chromosomes

Question 46

What is chromatin?

Answer 46

The combination of DNA and proteins before cell division

Question 47

What is the order of the cell cycle?

Answer 47

1. G1 2. S 3. G2 4. M **Cytokinesis is not included as it it optional**

Question 48

What does interphase refer to ?

Answer 48

All stages of the cell cycle except for M phase

Question 49

True or False: Most cells in your body have not divided in a long time?

Answer 49

True

Question 50

In what phase do most cells stop cycling?

Answer 50

G1

Question 51

What does the S to G2 checkpoint look for?

Answer 51

Internal signals that tell the cell that all of the DNA has been replicated

Question 52

What does the G1 to S checkpoint look for?

Answer 52

External chemical signals from other cells

Question 53

What is the basis of cancer? I

Answer 53

If something goes wrong with the checkpoint controls that regulate cell division, cells divide continuously and at the wrong time, this can cause cancer