DNA packaging

chromatin

in non-dividing cells, a complex of DNA and histones that compresses to form chromosomes

histones

small, positively charged proteins that compact chromosomal DNA into the microscopic space of the eukaryotic nucleus, 8 subunits make up a histone

nucleosomes

structural unit of a chromosome that consists of a length of DNA coiled around histones

30 nm fiber

chromatin that is coiled into a short, thick fiber that is 30 nanometers in diameter so it can fit in the nucleus

chromatid

the two halves of a duplicated chromosome (each one is a "sister chromatid")

centromere

holds the sister chromatids together

chromosome

in dividing cells, the thread-like structure in which DNA is packaged into, each one carries a specific gene

linker DNA

the DNA that joins nucleosomes to one another in chromosomes

diploid

having two complete sets of chromosomes, one from each parent

eukaryotic DNA

shape: linear

proteins to help pack? yes (histones)

# chromosomes: varies (2+)

extra genetic material? yes (introns)

prokaryotic DNA

shape: circular

proteins to help pack? no

# chromosomes: 1

extra genetic material? no

how many chromosomes do humans have?

46

how does the size of the genome relate to the complexity of the organism?

the larger the genome, the more complex the organism

genome

all of the genetic material in an organism

before a cell can divide, what must happen?

-DNA must be duplicated

-organelles must be duplicated

-cell must grow

-cytoplasm must be made

interphase

-before mitotic (M) phase

-consists of the steps G1, S and G2

-G1 phase = gap 1 phase, where the cell grows

-S phase = synthesis phase, where DNA is replicated

-G2 phase = gap 2 phase, cell grows again

mitotic (M) phase

-after interphase

-consists of the steps mitosis and cytokinesis

-mitosis = division of the nucleus

-cytokinesis = cell splits in two

G1 phase (gap 1 phase)

the first stage of the cell cycle (part of interphase) where the cell grows

S phase (synthesis phase)

the second stage of the cell cycle (part of interphase) where the DNA is replicated

G2 phase (gap 2 phase)

the third stage of the cell cycle (part of interphase) where the cell grows again

M phase (mitosis)

the fourth step of the cell cycle (part of the mitotic phase) where the nucleus divides

cytokinesis

-the fifth step of the cell cycle (part of the mitotic phase) where the cell splits into two

-division of the cytoplasm

-at the same time as telophase

-in animals, a cleavage furrow is formed which pinches the cell into two daughter cells

-in plant cells, a cell plate is formed and grows outward to create a new cell wall

the cell cycle

the continuous cycle of how cells divide, as soon as cells exit the cycle all cells go back in. includes the steps (in this order) G1, S, G2, M, cytokinesis

can prokaryotes preform mitosis?

no, because they do not have a nucleus

growth factor

increases rate of the cell cycle. it is a protein secreted by certain body cells that simulates other cells to divide. different cells have different growth factors.

external regulator

proteins that respond to the environment outside the cell

density dependent inhibition

decreases rate of the cell cycle. it is a phenomenon where crowded cells stop dividing once the place they operate in is dense enough. cancerous cells do not have a DDI

cell cycle control system

-a cyclically operating set of molecules in the cell that triggers and coordinates key events in the cell

-checkpoints are like stoplights

G1 checkpoint

-determines whether a cell will divide or go to G zero

-if a cell receives a go signal, it may continue in the cycle

-if it receives a stop signal, it enters G zero, a non-dividing stage

-most cells actually exist in G zero

P53

-"guardian on the genome"

-regulates cell cycle, also a tumor suppressor gene

does this in two ways:

-activate the DNA repair pathways

-stop signal at G1 checkpoint for DNA repair

-initiate apoptosis (programmed cell death if DNA damage is too extensive)

cell cycle regulatory proteins

-cyclins

-cyclin dependent kinases

-activate when a cyclin binds to them

-always present but not always on

MPF

-maturation promoting factor

-cyclin-CDK complex that triggers cells' passage past the G2 checkpoint into the M phase

-promotes mitosis

G2 checkpoint

-chromosomes must be replicated successfully

-DNA must be undamaged

-activated MPF must be present

-is there two of everything so the daughter cells will both have everything?

M checkpoint

-ensures that all chromosomes have lined up on the metaphase plate before the sister chromatids

-this makes sure that each daughter cell will have a copy of each chromosome

oncogene

-a gene that has the potential to cause cancer

-it helps cancer escape death (apoptosis)

tumor

abnormally growing mass of cells. 2 types:

benign: harmless, stays in same location (but CAN become malignant

malignant: harmful, spreads into neighboring tissues

metastasis

when a tumor spreads (from the primary tumor) through the circulatory system to another body location (secondary tumor)

naming cancers

-cancers are named based on their site of origin

carcinomas: external/internal body covering

sarcomas: tissues that support body

leukemias: blood forming tissues

lymphomas: lymph nodes, immune system tissues

what does a cell in interphase look like under a microscope?

black blob, individual chromosomes not visible

phase 1 of mitosis

PROPHASE

-sister chromatids (duplicated chromosomes) are condensed

-mitotic spindle (microtubules) begin to form in the cytoplasm, begin to grow out of the centrosomes (these make sure each cell gets the right DNA)

-centrosomes move away from each other

-in the last part of this stage, the nuclear envelope begins to break down

what does a cell in prophase look like under a microscope?

black blob with more individual chromosomes

phase 2 of mitosis

METAPHASE

-sister chromatids line up along the metaphase plate (the process may not proceed until all of them line up)

-mitotic spindle is fully formed

-centrosomes are now at opposite poles

-nuclear envelope is gone

what does a cell in metaphase look like under a microscope?

all of the chromosomes in the middle

centriole

an organelle near the nucleus in animal cells, occurring in pairs and involved in the development of spindle fibers in cell division

centrosome

organelle near the nucleus of a cell that contains the centrioles (in animal cells) and from which the spindle fibers develop in cell division

phase 3 of mitosis

ANAPHASE

-sister chromatids pulled apart by motor proteins (they move to opposite poles)

-they are now daughter chromosomes

-spindle apparatus: fibers push apart to opposite sides

-still no nuclear envelope

what does a cell in anaphase look like under a microscope?

chromosomes on either pole

phase 4 of mitosis

TELOPHASE

-chromosomes begins to de-condense to form chromatin

-spindle apparatus disintegrates

-nuclear envelopes appear around chromosomes at the poles

-cell elongation continues

what does a cell in telophase look like under a microscope?

2 dark, dense blobs on either pole

mitotic spindle

-contains two types of microtubules

POLAR: extend from each spindle and overlap through the cell

KINETOCHORE: attach to chromosomes

epigenetics

chemical modifications due to the environment

impact gene expression

-methylation of cytosine (addition of methyl group)

-acetylation of histones (addition of acetyl group)

unmethylated cytosine, acetylated histones:

-switch goes ON

-DNA loosely packed ("active/open chromatin")

-transcription possible

methylated cytosine, deaceylated histones:

-switch goes OFF

-DNA tightly packed ("silent/condensed chromatin")

-prevents transcription

calculating a mitotic index

(# of cells in mitosis) divided by (total # of cells) = percentage mitotic index

mutagen

agent that causes changes in the genetic material of an organism, can be physical, biological or chemical

carcinogen

a mutagen that leads to the formation of cancer

primary tumor

original location of the tumor

secondary tumor

the place to which the tumor spread

asexual reproduction

reproduction that creates genetically identical offspring (mitosis)

sexual reproduction

2 gamete unite to form genetically different offspring (meiosis)

meiosis 1

first cell division in which synapsis and crossing over occur, 2 daughter cells are produced that have half as many chromosomes as the parent

crossing over

occurs in prophase 1. paternal and maternal chromatids break and rejoin at chiasmata, then each chromatid has maternal and paternal DNA

gametes

sex cells (egg and sperm)

somatic cells

all other body cells (non-sex cells)

meiosis 2

second cell division in meiosis in which sister chromatids separate, similar to mitosis

non-sister chromatids

chromosomes that aren't connected but are in the same homologous pair

haploid

having one copy of each chromosome

homologous chromosome

the paternal and maternal pair chromosome (i.e. #23 from both mom and dad)

synapsis

the pairing of homologous chromosomes

prophase 1 (meiosis)

chromosomes condense, nuclear envelope breaks, spindle apparatus forms, synapsis of homologous chromosomes, crossing over of non-sister chromatids

metaphase 1 (meiosis)

migration of tetrads to metaphase plate is complete

anaphase 1 (meiosis)

homologs separate and begin moving to opposite poles

telophase 1 (meiosis)

chromosomes move to opposite sides of the cell

cytokinesis 1 (meiosis)

cell (cytoplasm) divides

meiosis

in sexually reproducing cells, 2 stage cell division to produce 4 haploid cells from 1 diploid, halving the chromosome number

chiasmata

the x-shaped structure formed during meiosis when non-sister chromatids (homologous chromosomes) cross over

prophase 2 (meiosis)

spindle apparatus forms

metaphase 2 (meiosis)

chromosomes line up at the metaphase plate (middle of the cell)

anaphase 2 (meiosis)

sister chromatids separate, begin moving to opposite sides of the cell

telophase 2 (meiosis)

chromosomes move to opposite sides of the cell

cytokinesis 2 (meiosis)

cell (cytoplasm) divides

why is it crucial that gametes reduce their number in half?

so they can pair with the other parent's gamete and create a cell with the normal number of chromosomes that has half it's DNA from each parent

why do homologous chromosomes separate during meiosis?

because they need to be equally distributed in the daughter cells and make sure that each daughter cell has a copy of each gene from both parents

how does meiosis create genetic diversity?

-crossing over

-random alignment and separation

problems from meiosis?

if both homologs or sister chromatids move to the same pole of the parent cell, meiosis will be abnormal because of too much DNA

karyotype

pictures of the chromosomes inside a cell, from these one can tell the gender and any abnormalities

XX

female

XY

male

steps for making a karyotype

1. get cells

2. visualize chromosomes

3. organize chromosomes

1 - getting cells

-for newborns/children/adults, blood must be drawn

-for fetuses, the mother must undergo amniocentesis or chorionic villus sampling (CVS)

amniocentesis

-use needle to extract amniotic fluid from the womb (fetal cells found there)

-miscarriage rate: 1 in 1000

-can be done at 15 weeks or later

chorionic villus sampling (CVS)

-catheter inserted into vagina to collect fetal cells found on placenta

-miscarriage: 1 in 100

-can be done at 10-12 weeks

2 - visualize chromosomes

-find cells that are actively dividing

-chromosomes are dyed so they can be seen

-chromosomes are photographed in metaphase

3 - organize chromosomes

-homologous chromosomes paired

-scientists can analyze for normality/gender

"normal" karyotype

-46 chromosomes (23 pairs)

-22 pairs of homologous autosomes

-23rd pair = sex chromosomes

trisomy

3 copies of one chromosomes instead of 2

monosomy

1 copy of one chromosome instead of 2

trisomy 21

down syndrome

non-disjunction

the failure of homologs or sister chromatids to separate