General Biology 1- Exam 3

pRb

tumor suppressor; inhibits cancer

Cell reproduction is

similar in all living organisms

Cell division in unicellular organisms

every time you divide or reproduce, you are making a new being

Cell division in multicellular organisms

use cell division for many different things
-reproduction
-growth (addition of cells)
-tissue repair
-regeneration

4 Steps of cell division

1. Signal
2. DNA and cellular components replicate
3. Distribution
4. Membrane separates

Signaling (step 1 cell division)

before a cell may divide, it needs a signal to tell it to divide

Distribution (step 3 cell division)

equally distribute material to new cells

Membran separates (step 4 cell division)

separates into 2 separate cells

Prokaryotic Cell

unicellular
1 circular chromosome
no nucleus

How do prokaryotic cells divide

fission

Cell Reproduction in Prokaryotes

1. Have 1 ORI (origin of replication)
2. Replicate the singular chromosome
3. Chromosome attaches to plasma membrane
4. As the cell grows, new plasma membrane will be added between the two copies of DNA
5. Cytokinesis occurs at the end
-divide this one cell into two, each will have a chromosome

Eukaryotic Cells

-have a nucleus that defines them
*Nuclear information divided between 2 cells
-have multiple chromosomes
-multiple origins of replication

Two ways to divide eukaryotic cells

1. Mitosis (create an identical cell/clone)
2. Meiosis (only occurs in the gametes, specialized cell division for sexual
reproduction)

In meiosis, genetic information in chromosomes is shuffled, divided into gametes which means the gametes only have

half of the genetic material of the chromosomes

Cell Cycle for eukaryotic cells

-regulate whether or not cells divide
-Two major phases:
*Mitosis
*Interphase

Interphase

period between division of the cell
-the cell spends most of its time here
-has 3 phases
1. G1: Gap 1: just after mitosis, before DNA synthesis: cell grow
2. S: S phase: DNA synthesizes (replicates)
3. G2: Gap 2: prior to M phase, microtubule organizers will be assembled,
serves as a checkpoint that all DNA was replicated properly

Cell cycle regulator function

regulate the cell cycle

Checkpoints in the cell cycle

1. G1-->S (signaling)
2. G2-->M (before divided, must be looked at)
3. Transition between metaphase and anaphase in mitosis

Checkpoints are regulated by

-cyclin (protein)
-cyclin will activate another enzyme (CDK), cyclin dependent kinase
*Will phosphorylate a substrate (use ATP)
*Kinase will only act if cyclin is present
*Cyclin is only made when you want to progress though a checkpoint

Controlling Transition of G to S

- cell cycle control is important; you don't want cells to divide unless they
receive a signal

pRb gene

-identified in retinoblastoma, a growth factor binds to receptor, causes cyclin to be made
1. cyclin binds to cdk,
2. cdk phosphorylates RB, signals DNA replication (S phase)
*Normally when active, not phosphorylated and inhibits cell cycle
progression
*When you phosphorylate pRb, you inactivate it and the cell cycle
continues

p53

will recognize when DNA is damaged and will inhibit phosphorylation of pRb
*makes sure you do not replicate damaged DNA

p53 and pRb are

tumor suppressors

Oncogene

can cause cells to replicate too often (growth factors)

Eukaryotic Chromosomes

-have lots of linear, double-stranded DNA
-associated with many proteins
*Referred to as chromatin

Eukaryotic Chromosomes during S phase,

will replicate and will have sister chromatid which are joined

Histone

protein DNA is associated with

Nucleosome

DNA associated with a core of 8 histone proteins

DNA is less condensed during

interphase
*use DNA to either replicate or to make proteins

During mitosis, DNA is tightly condensed so you can

equally separate it between 2 cells

Mitosis

-make an identical copy of your cell's "clone"
-to prepare for mitosis, DNA is replicated during S phase (not mitosis)
*Replication of centrosome
-need 2 to set up mitotic spindle
*Transition from being G2-->Mitosis
*Centrosomes will separate to opposite poles
-sets up plane of division

4 Stages of mitosis

1. Prophase
2. Metaphase
3. Anaphase
4. Telophase

Prophase

-beginning of mitosis
-chromosomes will begin to compact, they condense, held together by
cohesion
-microtubules will begin to form
*Tracks, chromosomes will move along microtubules later in mitosis
-kinetochores will form around the centromere of your chromosomes

Pro/Meta phase

-nuclear lamina begins to break down as well as the nuclear envelope

Metaphase

-kinetochores are going to arrive at the metaphase plate (Equitorial plate)
*Chromosomes are now at the middle of the cell
-microtubules are associated with kinetochores
*Once they are at the plate, metaphase is over

Cohesion

holds chromosomes together; nothing separates until the mitotic spindle is in contact with each kinetochore located at the centromere

Anaphase

-the centromere region at the kinetochore will separate and sister chromatids will go to opposite poles of cells
-moved along microtubules

Telophase

- creates identical clones
- the end, chromosomes stop moving
- rebuild the nuclear lamina and nuclear envelope

Karyotype

photograph of chromosomes during metaphase; chromosomes are able to be separated and organized based on size, number, and shape

Chromosomal painting

each chromosome has its own color

Cytokinesis

division of cell and cytoplasm

Cytokinesis in animal cells

-no cell walls
-use furrowing; divide by furrowing
*a ring made of actin and myosin, it will slowly constrict around the cell
membrane and pinch the cells into 2

Cytokinesis in plant cells

-have a plant cell wall and plasma membrane
*Plants will divide by forming little Golgi vesicles which fuse in the middle,
form a cell plate which expands until it separates the 2 cells

Asexual reproduction involves

mitosis (identical copies)

Sexual reproduction involves

meiosis and the combination of gametes (sex cells)
*During meiosis, you will produce 4 cells (progeny) that are genetically
unique
*You make gametes, gametogenesis
*2 gametes, 1 from each parent, fuse to make a zygote (first cell)

Somatic cells

all of the cells in your body besides the gametes (sex cells); contain 2 sets of chromosomes 1 from mom, 1 from dad, homologous
*Somatic cells all go through mitosis
*Do not contribute to the next generation

Homologous chromosomes

a pair of chromosomes that have corresponding, but not identical genetic information
*Haploid cells: 1 copy (1n), product of meiosis (ex. gametes)
*Diploid cells: (2n), created when 2 haploid cells fuse (ex. somatic cells)

DNA purposes

-replication
-reading for instruction

Cohesion is cleaved by

separase; lets sister chromatids separate during anaphase

Eukaryotes are classified by

how long they spend in the 1n or 2n phase

3 Categories of Eukaryotes

1. Haplontic Life cycle
2. Alteration of generations
3. Diplontic life cycle

Haplontic Life cycle (eukaryotes)

-predominant life cycle is a 1n haploid individual

Alteration of Generation (eukaryotes)

-includes a 1n multicellular stage and a 2n multicellular stage and spend half of their life in both

Diplontic Life cycle (eukaryotes)

-seen in most mammals
-only time you have a haploid is gamete form, the rest is diploid

Meiosis

consists of 2 nuclear divisions
-reduce number of chromosomes from diploid to haploid
-DNA will only be replicated once before meiosis occurs

Functions of Meiosis

1. reduce chromosomes from diploid to haploid
2. ensure each gamete gets a complete set of chromosomes
3. promote genetic diversity

Meiosis I

DNA was replicated

Prophase I

-synapsis between homologous chromosomes
-this is when chromosomes are joined by a complex of proteins and form a tetrad
-tetrads can cross over at a point known as a chiasmata

Tetrads

2 homologous chromosomes with sister chromatids

Crossing over

increases genetic variation/diversity by exchanging genes on homologous chromosomes
*recombination/ recombinants
*Only during meiosis

Metaphase

align chromosomes on equatorial plate

Anaphase I

independent assortment
-homologous chromosomes are going to separate, not sister
chromatids
which chromosome goes to either cell is a matter of chance
-reshuffling of genetic material

Telophase I

-chromosomes stop moving
-nuclear envelope splits

Meiosis II

1. Prophase II
2. Metaphase II
3. Anaphase II
4. Telophase II

Anaphase II

separate sister chromatids

Telophase II

4 genetically different gametes are produced (1N)

Nondisjunction

-homologous chromosomes fail to separate during anaphase I
-sister chromatids fail to separate during anaphase II

Cireploidy

incorrect number of chromosomes

Monosomy

missing 1 chromosome

Trisomy

have an additional chromosome
-trisomy 21: downs syndrome

Translocation

-occurs when chromosomes align for crossing over and they are incorrect chromosomes; not homologous
-a part of one chromosome us going to attach to another that is not homologous

Cri Du Chat

occurs because of a translocation
-affects development of larynx
-cancer: leukemia

Meiosis complications can create

polyploids in plants
-they have an entire extra set of chromosomes
*Triploid (3N)
*Tetraploids (4N)

Necrosis (cell death)

a messy cell death: cells are damaged: starved of nutrients, poisoned, burned, infected

Apoptosis (cell death)

programmed cell death, cells die because they are no longer needed
-a key enzyme us caspases
-involves a signaling cascade
-good for chemotherapy

Reason Mendel uses seeds and plants in genetics

-grown in large quantities
-large # of offspring
-short generation time
-male and female reproductive organs are present in plants
*Allows for self-fertilization
-control mating

Joseph Kolreuter

observed reciprocal crosses
-allowed him to see that both male and female gametes contributed
equally to the characteristics seen in offspring

Blending (Kolreuter)

traits from the mom and dad will mix and they will never be separated again
-Mendel proved this was incorrect

Mendel figured out

the laws of inheritance in plants

Gregor Mendel looks at

heritable characters and traits of characters

Characters

observable features (category)
-seed shape

Traits

form of character
-wrinkly or smooth

In order to study, Mendel had to

create true breeding peas
-inbreed for many generations so that all characters have the same
trait

Monohybrid cross

one trait

Dihybrid cross

two traits

Parental Generation (P)

the true breeding individuals that were used; what you start with

First Filial Generation (F1)

the cross of the P generation and their progeny

Subsequent Generation (F2)

offspring of the F1 generation

Mendel's First experiment

monohybrid cross looking at 1 character
-looked at seed shape
-F1 Generation: all seeds were smooth/spherical, no wrinkled
-Cross F1, in F2 there is 3 smooth, 1 wrinkled seed
-theory of blending does not hold true

Phenotype

the physical appearance of an allele in a gene (physically see from alleles)

Genotype

composition of the organism's alleles for a gene (made of 2 alleles)

Gene

a portion of the chromosome, will reside at one spot called the locus
-each gene is going to code for a specific protein function or
character

Allele

a different form of a gene
-each individual has 2 alleles for each gene

True breeding

homozygous
-SS
-ss

Heterozygous breeding

two forms of an allele
-Ss
-sS

Dominant

one allele will determine the phenotype in the heterozygous form

Recessive

hidden in the presence of a dominant allele

Mendel's Conclusions (genes)

the inheritable units are discrete particles
-these exist in pairs and separate during gamete formation

Mendel's Conclusions (alleles)

each pea had 2 units of inheritance for each character

Mendel's Conclusions (meiosis)

one unit is passed to the gamete when the gamete is formed