bio exam 2 h

Functions of cell division

reproduction
growth and development
tissue renewal

Genome
Prokaryotic vs. Prokaryotic

all DNA in a cell
Prokaryotic- single DNA molecule
Eukaryotic- several DNA molecules
DNA molecules in cell are packages into chromosomes

Chromatin

Eukaryotic chromosomes consist of chromatin, a complex DNA and protein that condenses during cell division

Ploidy

\# of chromosomes in a cell

Haploid cell (n)

one copy of each chromosome (Gametes\=sex cells)

Diploid cell (2n)

two copies of each chromosome (one inherited from mom one inherited from dad)

Somatic cell

body cell (2n)

Interphase

cell growth and DNA replication
90% of cell cycle
divided into 3 sub phases
GROWS DURING ALL 3 PHASES

G1 phase

first gap, growing phase

S phase

DNA is replicated, chromosomes double

G2 Phase

second gap, grows again

Mitotic (M) Phase

mitosis and cytokinesis

G1-gap 1
-ploidy
-function

Ploidy\=2n (animal cell, somatic cell)
No DNA synthesis
cell functions and communicates
protein manufactures
most of cell life is in G1

S-synthesis
-ploidy
-function

chromosomes duplicate
ploidy\=2n to 2n
DNA and chromosomes are synthesized
sister chromatids are identical

G2-gap 2
-ploidy
-function

ploidy\=2n
centrosome duplicate- made up of centrioles

5 phases of Eukaryotic cell division

1. prophase
2. pro-metaphase
3. metaphase
4. anaphase
5. telophase

Prophase

-chromosomes condense, become visible
-Mitotic spindle begins to form (microtubules)
-Centrosomes move away from each other to opposite poles
-Organizes DNA

PRO-metaphase

-nuclear envelope begin to break down
-nucleolus disappears
-mitotic spindle elongates
-chromosomes become more condensed
-some microtubules connect to kinetochordes handles
-drive movement this connection ends pro-metaphase and metaphase begins

Metaphase

-LONGEST STAGE
-centrosomes are at complete opposite ends of cell
-chromosomes align on the metaphase plate( the midway point btwn the spindles two poles)
-each chromosome is now attached to the kinetochore microtubules

Anaphase

-SHORTEST STAGE
-cohesion proteins are cleaved (allowing chromatids to separate
-chromosomes begin to move to opposite sides
-at the end of this phase there are two complete sets of chromosomes 2n on each side of cell
-still diploid 2n (animals always diploid)

Telophase/Cytokinesis

-the tow new daughter cells form
-the nuclear envelope reforms
-nucleoli appears
-cytokinesis has already begun and will divide cells with cleavage furrow
-CYTOKINESIS NOT APART OF MITOSIS
-cytoplasm divides
-each daughter cell gets one centriole
process varies between plant and animal cell
-retrieves to interphase

Process of binary fission (4 steps)

1. chromosome replication begins
2. one copy of the origin is now at each end
3. replication finishes
4. two daughter cells

2n\=2n

MITOSIS

Asexual Reproduction
-how many parents?
-does this organism go through mitosis or meiosis?
-what does this produce?
-advantages/disadvantages

-one parents
-mitosis
-clones
-advantages, always the same offspring
-disadvantages, always the same mutations take a toll (clones will get all the benefits and mistakes of its parent)

Sexual Reproduction
-how many parents?
-does this organism go through mitosis or meiosis?
-what does this produce?
-advantages/disadvantages

-two parents
-meiosis
-variable
-advantage, genetic variation
-disadvantage, hard to find a partner

Human chromosomes

46 chromosome
23 pairs of homologs
-1 pairs if sex chromosomes (XX or XY)
-22 pairs of autosomes (body chromosomes)

Fertilization and Meiosis
4 facts

1. sexual reproduction
2. makes sure each offspring has same number of chromosomes
3.haploid and diploid alternate during life cycle
4.timing of 2 events varies among species

Haploid and diploid alternate life cycle

-2n-multicellular diploid stage (sporophyte) alternated with the
-n-multicellular haploid state (gametophyte)

Meiosis

-like mitosis: replication of DNA before meiosis
-NOT A CYCLE
-results in 4 daughter cells (haploid cells\= 1 copy of chromosome)

4 stages of Meiosis

1. interphase same as mitosis (G1, S, G2)
2. meiosis 1 (prophase, metaphase, anaphase, telophase, PMAT)
3. interkinesis
4. Meiosis II (PMAT)

Meiosis interphase

-same as mitosis
-chromosomes duplicate & centrioles replicate
-each chromosome is composed of two sister chromatids exact copies
-ploidy\=2n (still diploid just double the mass of DNA)
-humans (46\=2n 23 chromatids AFTER DUPLICATION 92 chromatids)

Meiosis I summary

-HOMOLOGOUS chromosomes separate resulting in 2 haploid (n) daughter cells
-2n\-----\> 2 x n
-diploid to 2 cells that are haploid
each
-each chromosome still consists of two sister chromatids

Prophase 1

-same as mitosis
- EXCEPT each chromosome pairs with it homolog, aligned gene by gene and crossing over occurs: the DNA molecules of non sister chromatids are broken by proteins and are rejoined to each other
-cell is diploid

Chiasmata

where crossing over has occurred in Prophase 1

Metaphase 1

-homologs pairs line up at the metaphase plate
-microtubules from poles attached to kinetochore of the chromosome

Anaphase 1

-homologous pairs separate
-sister chromatids remain attached at centromere and move as one unit to pole
disjunction-separate
nondisjunction-if it goes wrong

Telophase 1 and Cytokinesis

- each half of the cell has a complete haploid set of duplicated chromosomes
-each chromosome is composed of two sister chromatids - one or both regions contain regions of non sister chromatid
-cytokinesis occurs simultaneously

Interkinesis

no chromosome replication occurs
because the chromosomes are already replicated
-does not go through S phase again

Meiosis II

-sister chromatids separate
-4 haploid (n) daighter cells
-division occurs like meiosis

Prophase II

-spindle forms
-chromosomes \= pair of sister chromatids

Metaphase II

-sister chromatids line up on the metaphase plate
-tow sister chromatids of each chromosome are not identical
-kinetochores of sister chromatids attach to microtubules extending from opposite poles

Anaphase II

-sister chromatids separate
-sister chromatids of each chromosome now move as two newly individual chromosomes towards opposite poles

Telophase II/ Cytokinesis

-chromosomes arrive at opposite poles
-Nuclei forms and chromosomes decondense
-4 haploid daughter cells are formed

Gene

unit of heredity

Allele

alternative version of gene

Character

observable heritable feature

Trait

detectable variable of variable

Genotype

genetic makeup, what alleles are present (not seen)

Phenotype

observable physical traits (can see)

Why did Mendel use pea plants?
(6 reasons)

1. inexpensive
2. many varieties
3. easy to grow
4. large \# of offspring
5. choose clearly identifiable traits
6. easy to control pollination

Blending hypothesis

to test this hypothesis Medal crossed "true breeding" plants with contrasting traits
P\=parental generation- PXW
F1\=first filial generation- all plants were purple
F2\=second filial generation: 3:1 purple:white
no intermediate phenotypes appeared
Mendel rejected blending hypothesis

Mendel's developed hypothesis that explains the 3:1 inheritance pattern
(4 related concepts)

1. alleles- alternative versions of genes
2. 2 alleles inherited - 1 from each parent
3. dominant and recessive alleles
4. two principles of heredity (Mendel's Law)

Concept \#1. alleles

alternative versions of genes (codes for protein in DNA on chromosome)
each gene is at same locus (location) on homologous chromosomes

Concept \#2. two alleles one inherited from each parent

two alleles may be identical as in the true breeding plants
(P generation)- same homozygous
or
may be different
(F1 hybrids) - heterozygous

Concept \#3. dominant & recessive

if two alleles at a locus are different, then dominant allele determines the organisms appearance

Concept \#4. Mendel's Law

law of segregation- each gamete gets 1 allele for every trait

law of independent assortment- two alleles for a character segregate during gamete formation (meiosis)

Limitations of Mendel's law of independent assortment

today this law applies only to genes
genes located near each other n the same X tend to be inherited together (we call them linked)
Mendel did not know this

Multiplication rule

predicts combined probability of independent events (one does no affect probability of other to occur
(P)this and (P)that
word "and" means to multiply

The chromosome theory of inheritance
-what did it suggest?
-what was the experiment

Thomas Hunt Morgan
-evidence that chromosomes are the location of Mendel's law of heritable factors
-Drosophila , fruit fly (4 pairs of chromosomes, 3 pairs of autosomes, 1 pair of sex chromosomes) diploid \#\=8

Wild type

phenotype most observed in population
(red eyes in Drosophila)

Mutation phenotype

alternatives to wild type
(white eyes in Drosophila)

Sex linked gene

-can be located on either sex chromosome X or Y

Y linked gene

on the Y (few of these) most are related to sex determination

X linked gene

on the X, has as many genes as an autosome, not all determine sex

X linked recessive disorders

more common in males than females
ex: red/green color blindness

X inactivation in female mammals (BARR BODY)

functionally females are actually hemizygous because 1 X out of the XX is randomly inactivated during embryonic development

Linked genes

on the same chromosome tend to be inherited together

Complete linkage

2 genes are inherited as a single unit , close together on same chromosome

parental genotype 100 %
recombination genotype 0

must be on same chromosome

Incomplete linkage

independently assorted

parental genotype \#\> 50%-105% chance they show up together
Recombination genotype \#\> 0 and50%

must be on same chromosome

Unlinked

show up together 1/2 of the time- supports Mendel

parental genotype 50%
recombination genotype 50%

can be or could not be on same chromosome

The closer genes are the lower the.....

the lower the probability there will be for genetic recombination

Structure of nucleotide

1. phosphate group
2. sugar (deoxyribose)
3. nitrogenous base

pyrimidine

one ring
cytosine
thymine

Puradine

two rings
adenine
guanine

James Watson & Francis Crick

determined structure of DNA (1953) by using information from previous researchers
- Rosalind Franklin and Maurice Wilkins (1951-53)
-Erwin Chargaff (1949)

Rosalind Franklin (1951-53)

X-ray defraction determined 3D structures of molecules her image of DNA enabled Watson and Crick to deduce
1. DNA was helical
2. made up of 2 strands forming a double helix
3. width of helix
4. distance between turns
5. nucleotides bases stacked like rings on latter

Erwin Chargaff's rule (1949)

1. base composition of DNA varies between species
2. total purine (A+G)\= total puradine (C+T)
amount of A\= amount of T
amount of G\=amount of C
but A+T does not equal G+C

Double helix

composed of two strands of DNA each strand has a

1. sugar phosphate back bone outside of helix (rails of latter)
joined 3' 5' by phosphodiester linkages
no variability

2. 4 nitrogenous bases
attached to back bone by covalent bonds
lots of variability

Two strands on DNA

1. held by hydrogen bonds between
A+T
G+C
2. strands run antiparallel
run in opposite directions
3' to 5'
5' to 3'
3. ends at two strands differ
3' end- free 3' hydroxyl (OH)
5' end - free 5' phosphate

Semi conservative DNA replication

each new molecule of DNA contains
1 parental strand
and a newly synthesized strand

Process DNA initiation
part 1
part 2
part 3

part 1. origin of replication, DNA strands are separated from replication bubble, replication process out along fork
part 2. 3 proteins for unwinding
part 3. two proteins start replication

DNA helicase

untwists double helix at the replication forks

Single stranded binding proteins

SSBP's prevent closing of DNA strands

Topoisomerase

corrects overwinding down the DNA strand-prevents knots

Primase

synthesis RNA primer- initial nucleotide strand is a short RNA primer 5-10
nucleotides with an open 3' end (starting point for new DNA strand

these 5-10 nucleotides are what signals where DNA polymerase should begin synthesizing new DNA strand

DNA polymerase

builds new strand, it can only add nucleotides to an existing 3' end

Process elongation

DNA polymerase catalyze the elongation of new DNA always 5' to 3' (link of 5' P to 3' OH group)

Nucleoside triphosphate

building block\= nucleoside (base+sugar)

Leading strand

growing toward fork continuously

Lagging strand

growing away from fork discontinuous fragments called Okazaki fragments

Okazaki Fragments

RNA polymerase-sequence of DNA- RNA polymerase- Sequence of DNA

Mutation

change in nucleotide sequence of DNA
permanent change in daughter molecule - evolutionary significance
-source of variation and new alleles

Beadle and Tatum (1920s) hypothesis

each gene dictates production of a specific enzyme

now known: all proteins are enzymes
one gene\=one polypeptide/protein

Francis Cicle (1956)

proposed central dogma

Central dogma

DNA-RNA -protein

Transcription (first stage of gene expression)

info in DNA used to synthesize messengerRNA (mRNA)
occurs in all organisms
eukaryotes occurs in nucleus
prokaryotes occurs in cytosol

Translation (2nd stage of gene expression)

ribosome uses mRNA to synthesize polypeptide
occurs in all organism

mRNA

messenger RNA encodes an entire protein

rRNA

ribosomal RNA- structural part of ribosome

tRNA

transfer RNA carry individual amino acids to ribosome during translation