GenBio1: Cell Modification - Meiosis

specialized cells

• Designed to carry out a specific role, which has specific components and a specific structure.

1. trichomes

2. root hairs

3. palisade mesophyll

4. spongy mesophyll

plant specialized structures

trichomes

• Hair-like structures on leaves/stems

• Protect the plant from herbivores, reduce water loss, and trap insects to prevent damage.

root hairs

• Extensions of root epidermal cells

• Absorbs water and minerals from the soil

• Increases surface area for absorption

palisade mesophyll

• A layer of cells (like a solar panel) under the leaf’s upper surface

• Performs photosynthesis (contains lots of chloroplasts)

• Tightly packed and column-shaped for maximum light absorption.

spongy mesophyll

• Loosely packed cells below the palisade layer for gas exchange

• CO2 enters the stroma (1) or stromata (many)

1. microvilli

2. cilia

3. flagella

4. stereocilia

animal specialized structures

microvilli

• Tiny finger-like structures on cell surfaces (especially in the intestines).

• Increases surface area for absorption (like nutrients)

• Not for movement, just for absorbing only

cilia

• Short, hair-like structures

• Move fluids or particles over the cell (e.g., move mucus in the lungs)

• Can beat rhythmically

flagella

• Long, tail-like structure

• For movements such as the sperm cell tail

• Only a few per cell, but strong swimmers

stereocilia

• Long, non-motile microvilli (not true cilia)

• Found in the inner ear (for hearing) & the epididymis (sperm storage)

• For sensing or absorbing

1. sperm cells

2. egg cell (ovum)

sex cells

sperm cells

• Male reproductive cell

• Swim to and fertilize the egg

• Has a flagellum (tail), mitochondria for energy, and compact DNA

egg cell (ovum)

• Female reproductive cell

• Waits for fertilization; provides nutrients for early development

• Large size, lots of cytoplasm and organelles.

1. cell-matrix junction

   a. hemidesmosomes

   b. basal ba

2. cell-cell junctions

   a. tight junctions

   b. adherens junctions

   c. desmosomes

   d. gap junctions

cell junctions

cell-matric junction

connects the cell to the extracellular matrix (like the cell’s outside environment):

hemidesmosomes

• Anchor the cell to the basement membrane 

• Found in skin cells

basal infoldings

• Folds at the bottom of some cells

• Increases surface area for ion transport and secretion

cell-cell junctions

connect cells

tight junction

• Seal cells tightly together (like zippers)

• Prevent leakage between cells

adherens junctions

• Use actin filaments to connect cells

• Help cells stick together and maintain shape

desmosomes

• Strong “spot welds” between cells

• Resist stress

gap junctions

• Tiny channels between cells

• Let ions and molecules pass for cell communication

1. red blood cells (rbc)

2. white blood cells (wbc)

   a. monocytes

   b. eosinophil

   c. basophil

   d. lymphocytes

   e. neutrophil

blood cells

red blood cells

• Also called erythrocytes 

• Carry oxygen using hemoglobin

• Biconcave shape, no nucleus, flexible

white blood cells

• Help fight infections

monocytes

1.  become macrophages (destruction of bacteria and other harmful organisms) and eat invaders 

eosinophil

1.  fights parasites and allergies

basophil

1. releases histamine (in allergic reactions)

lymphocytes

1. B cells (make antibodies), T cells (attack cells)

neutrophil

1. first responders to bacteria

cell cycle

• Sequence of events that encompasses the period between the completion of one cell division and the end of the next division

karyokinesis

• division of cell’s nucleus

• the division of the nucleus, ensuring each daughter cell receives a complete set of chromosomes

cytokinesis

• division of cytoplasm

• the division of the cytoplasm following karyokinesis, resulting in the physical separation of the parent cell into two daughter cells.

1. mitosis

2. meiosis

2 types of nuclear division

1. interphase

   a. g1 phase

   b. s phase

   c. g2 phase

2. mitosis

   a. prophase

   b. prometaphase

   c. metaphase

   d. anaphase

   e. telophase

phases of cell cycle

interphase

A cell undergoes normal growth processes while also preparing for cell division.

g1 phase

• Nucleus and cell increase in size

• Chromosomes are fully extended

• The cell expels large amounts of energy in the synthesis of RNA and protein

• The cell carries out normal functions specific to its type

s phase (synthesis of DNA)

• DNA replication results in the formation of sister chromatids.

• The centrosome is duplicated, which will give rise to the mitotic spindle

• Centrioles are located at the center of each animal cell and play a crucial role in organizing cell division.

g2 phase

• The cell replenishes its energy stores and synthesizes proteins necessary for chromosome manipulation.

• Some cell organelles are duplicated

• There may be additional cell growth during this phase 

• The cytoskeleton become dismantled

mitosis

• The process by which the duplicated chromosomes are aligned, separated, and moved into two new, identical daughter cells. 

prophase

• Chromatin condensation

• Nuclear envelope breakdown

• Spindle formation

• Condensation and shortening of chromosome genetic material occur

prometaphase

• The nuclear envelope disintegrates. 

• The microtubules are allowed to extend from the centrosome to the chromosomes

• The microtubules attach to the kinetochores, which allow the cell to move the chromosomes around

metaphase

• Chromosome alignment in the center of the cell to ensure that each daughter cell will receive one chromatid from each chromosome

• Spindle attachment to the centromere of each chromosome

anaphase

• The splitting of the sister chromatids

• These sister chromatids become the chromosomes of the daughter nuclei.

telophase

• The nuclear envelope reforms around each set of separated sister chromatids

• The nucleolus, Golgi bodies, and the ER complex start to reappear

1. presence of essential nutrients

2. anchorage dependence

3. density dependent inhibition

4. growth factors

factors that affect cell division

anchorage dependence

The need for the cell to be in contact with a solid surface to divide

density dependent inhibition

• Crowded cells stop dividing

growth factors

• Proteins that stimulate division

• Easier for cells to divide with this factor

• Commitment to divide

• Size of cells

• Growth factor present

• No DNA damage

g1 checkpoint

• proper dna replication

g2 checkpoint

• all chromosomes are attached to the spindle fibers

m checkpoint

oncogenes

1. muted or over-expressed proto-oncogene that can lead to uncontrolled cell division, leading to a tumor if too much

proto-oncogene

1. genes that regulate cell division and promote normal cell division.

1. oncogene

   a. proto-oncogene

2. tumor suppressor gene

3. dna repair gene

genes and cancer

mitosis

• produces two daughter cells

• diploid

• make body cells (identical copies)

meiosis

• produces 4 daughter cells

• haploid

• make sex cells and makes them different

homologous chromosome

• Same size/length

• Same type of gene location

• Centrosome position

• Locus (plural, loci) - the position of a gene

human karyotype

• An individual connection of a chromosome

• Used to look for abnormal numbers of structures of chromosomes

meiosis 1: homologous chromosomes separate

• Meiosis follows the interphase, consisting of G1, S, and G2 phases, which are nearly identical to the phases preceding mitosis.

synapsis

• pairing of homologous chromosomes forming a tetrad, aligned by a protein structure called the synaptonemal structure

crossing over

• segments of DNA are exchanged between non-sister homologous chromatids. Can be observed visually after the exchange as chiasmata (singulr=chiasma). 

metaphase 1

• Homologous chromosome pairs (tetrad) align along the metaphase plate

• Spindle microtubules are attached to a kinetochore

anaphase 1

• Microtubulus pull the linked chromosomes apart

• Sister chromatids remain attached

• The chiasmata are broken as the microtubules attached to the fused kintochores pull

telophase 1 and cytokinesis

• separated chromosomes arrive at opposite poles.

• Two haploid cells are the result of the first meotic division

meiosis 2: sister chromatids separate

• Interkinesis lacks an S phase so chromosomes are not duplicated.

• The sister chromatids within the two daughter cells separate, forming four new haploid gametes

• Each diving cells has only one set of homologous chromosomes

• Therefore, each cell has half the number of sister chromatids to separate out as a diploid cell undergoing mitosis

prophase 2

• Chromosomes condense again just like in telophase 1

• Nuclear envelopes fragment into vesicles

• Centrosomes that were duplicated during interkinesis move away from each other toward opposite poles

• New spindles are formed.

metaphase 2

sister chromatids are maximally condensed and aligned at the equator of the cell

anaphase 2

• sister chromatids are pulled apart by the kinetochore microtubules and move toward opposite poles

Non-kinetochore microtubules elongate the cell, the homologous chromosomes apart

telophase 2 and cytokinesis

• Chromosome arrive at opposite poles and begin to decondense

• Nuclear enveloped form around the chromosomes

• Cytokinesis separates the two cells into four unique haploid cells

• Newly formed nuclei are both haploid