Animal genetics exam 1

cellular characteristics of prokaryotes

no nucleus, dna in nucleoid

cytoplasm w/ plasma membrane

rigid cell wall for outer membrane

genetic characteristics of prokaryotes

circular, often singular chromosome

asexual repro

horizontal gene transfer

characteristics of eukaryotic genetic material

mostly organized as linear chromosomes with circular mitochondrial DNA

chromatin

dna-protein complex of chromosomes, condensed during mitosis/meoisis to form chromosomes

what 2 things are chromosomes composed of

dna and proteins

telomere

repetitive sequences of nucleotides that maintain chromosome length during replication and protect its ends

centromere

segment of chromosome that provides attachment site for kinetochore during cell division

autosome

non sex chromosome

homologs

members of a pair of chromosomes that form a homologous pair

nearly identical in size, have same banding / centromere, have same genes but not necessarily same alleles

ploidy

number of sets of chromosomes in a cell

what does n indicate in terms of ploidy

number of chromosomes in a set

polyploidy

more than 2 sets of chromosomes, common in plants

goldfish have 100 chromosomes (4n=100)

how many chromosomes do they have in a single set (n)

25

aneuploidy

when there is a trisomy (extra chromosome) or monosomy (missing chromosome), usually resulting in embryonic loss

cytogenetics

field of genetics involving microscopic exam of chromosomes in actively dividing cells

chromosomes organized by size to create karyogram

cell cycle of eukaryotic cells

1. G 0

2. Interphase (G1, S, G2)

3. mitosis

G zero phase

resting phase in which a cell may have postponed progression, or will never divide again

interphase

where cell enters cell division, includs G1, S, and G2

G1 phase

aka gap 1 phase or the restriction point where cell preps to divide by checking for proper conditions and making molecular changes

S phase

aka synthesis phase or chromosome replication, 2 copies of replicated chromosome called chromatids are joined at centromere to form pair of sister chromatids

G2 phase

final preparation for cell division

which phases of the cell cycle have chromatids vs sister chromatids

G0, G1 and late mitosis (anaphase-cytokinesis) have chromatids

S, G2 and early mitosis have sisters

phases of mitosis

prophase, metaphase, anaphase, telophase

centrosome

attachment point of mitotic spindle that divide before mitosis, during interphase

prophase

first stage of mitosis where nuclear envelope dissociates into small vesicles and chromatids get compacted

mitotic spindle apparatus begins to form w/ microtubules

centrosomes begin to separate

late prophase

aka prometaphase, centrosomes move to opp. ends forming spindle poles

spindle fibers interact w/ sister chromatid and form apparatus

kinetochore microtubules grow from 2 poles and 2 kinetochores on pair of sister chromatids are attached to kinetochore microtubules on opp. poles

meiotic spindle apparatus

microtubules are formed by rapid polymerization of tubulin proteins

astral microtubules

position the spindle apparatus

polar microtubules

push poles away from each other

kinetochore microtubules

attach to kinetochore which is bound to centromere of each chromosome

metaphase

pairs of sister chromatids align themselves on metaphase plate

each pair of chromatids is attached to both poles via kinetochore microtubules

anaphase

connection holding sister chromatids together is broken, so each chromatid is attached to only one pole

kinetochore MTs shorten, chromatids move to opp. poles, polar MTs lengthen, poles move apart

telophase + cytokinesis

chromosomes reach respective poles and decondense

nuclear membrane reforms into 2 sep. nuclei

cytoplasm divides, creating cleavage furrow in animals and cell plate in plants

when does meiosis begin

after cell has progressed through interphase of cell cycle

phases of meoisis

meiosis I and II, 2 successive divisions to reduce chromosome content

meiosis I

‘reduction phase’ with prophase I, metaphase I, anaphase I, and telophase I

meiosis I: prophase I

recombination/crossing over of homologs

order of events during prophase I

1. leptotene

2. zygotene

3. pachytene

4. diplotene

5. diakinesis

Lovely zebras play dinosaur dance

leptotene

helps replicated chromosomes condense during prophase I

zygotene

during prophase I, causes synapsis beginning and bivalent forming

pachytene

during prophase I, bivalent is completely formed and helps crossing over to occur

chiasma is formed between chromosomes

diplotene

during prophase I, synaptonemal complex dissociates, making chiasma visible

diakinesis

during prophase I, nuclear envelope dissolves and spindle apparatus forms

meiosis notation

before: 2n, 4c

meiosis I: 1n,2C

meiosis II: 1n, 1c

meiosis II vs mitosis

similar, but

for diploid with 6 chromosomes, mitosis begins with 12 chromatids joined as 6 pairs of sister chromosomes, while meiosis II begins with 6 chromatids joined as 3 pairs of sister chromatids

if an animal has 60 chromosomes, how many chromosomes and chromatids does one of their cells have during the S phase of interphase?

60 chromosomes, 120 chromatids

requirements of the genetic material

information, transmission, replication, variation

nucleotide structure

phosphate group, pentose sugar, nitrogenous base

roles of nucleoside components

phosphate group links, pentose anchors, nitrogenous bases have data

phosphate group

attached to 5’ carbon and links to oxygen on 3’ carbon of sugar adjacent nucleotide

purine vs pyrimidine

both are nitrogenous bases, purines are 6 or 5 membered rings while pyridimines are 6 membered

phosphodiester bonds

link nucleotides together with phosphate connecting 5’ C of one nucleotide to the 3’ C of another, forming phosphodiester linkage

strand directionality

result of phosphodiester linkages, where DNA will always be 5’ to 3’

RNA structure

similar to DNA, but only 1 of 2 DNA strands used as template

Chargaff’s rule

% of adenine = % of thymine

% of cytosine = % of guanine

sum of purines = sum of pyridimines

a helix

secondary structure that proteins can fold into

structure of DNA double helix

2 antiparallel strands twisted around central axis

forms helix that is right handed, so as it spirals away from you it turns in clockwise direction

how is the double helix stabilized

hydrogen bonding between complementary bases

A bonds to T w/ 2 H bonds, C to G w/ 3 H bonds

also use base stacking

DNA double helix grooves

2 asymmetrical grooves on outside of helix (major and minor) of which certain proteins can bind to bases within

alternate helices

dna double helix can form diff secondary structures (A, B, and Z DNA) with B being what’s normally found in living cells

Z-DNA

left handed helix which may play role in transcription and chromosome structure

double stranded RNA

although rna is usually single stranded, it can form short double stranded regions for complementary base pairing

these helices are also usually right handed

central dogma of biology

dna → rna → proteins

is dna replication conservative?

semi conservative

basic structures of dna replication

2 template strands, one leading strand and one lagging strand

replisome

composed of the ingredients for dna replication

oriC

dna region that serves as ORIgin of Chromosomal replication

eukaryotes have multiple of these and dna synthesis proceeds bidirectionally

key dna sequences in the oriC

AT-rich region, DnaA box sequences, GATC methylation sites

AT-rich region

region of oriC where DNA strands begin to separate

DnaA box sequences

binding sites for DnaA proteins on oriC

GATC methylation sites

regulate replication in the oriC by having dna adenine methyltransferase methylating the A on both strands

initiation of replication only occurs on fully methylated dna and this prevents 2nd round of replication from occurring too early

how is replication initiated

DnaA proteins bind to DnaA boxes in specific order, helicase later binds to origin

DnaA

proteins that bind to DnaA boxes in specific order, causing DNA to bend while atp hydrolysis causes double helix to begin unwinding

strands are separated at AT rich region

helicase

binds to origin during replication initiation, further unwinding strands while traveling on them in 5’ to 3’ direction

uses energy from atp

creates replication bubble

replication bubble

helicase’s unwinding creates a bubble at each origin, each of which has 2 replication forks (1 on each end)

single strand binding proteins

bind to separated dna strands to keep them apart during replication

topoisomerase

travels ahead of helicase to alleviate the supercoils caused by helicase' unwinding

primase + rna primers

synthesizes short rna primers which are complimentary to dna near oriC and required to begin dna synthesis

DNA polymerase

breaks bonds connecting phosphate groups of nucleotide provides energy to form phosphodiester bonds between nucleotides in growing strand, held in place via sliding clamp on dna strand

moves from 5’ to 3’

leading strand

daughter strand synthesized from the single rna primer at origin

lagging strand

daughter strand synthesized from replication fork

many rna primers required, contains Okazaki fragments

DNA ligase

catalyzes formation of a covalent bond to connect the dna backbones recently put in place by dna polymerase

what makes mistakes during replication so rare?

• stability of base pairing

• structure of the dna polymerase active site

• proofreading function of dna polymerase

how does dna polymerase proofread

mismatch causes it to pause and leave mismatched nucleotide near 3’ end, which enters the exonuclease site

at this site, the strand is digested in 3’ to 5’ direction until incorrect nucleotide is removed

telomeres

noncoding, repeated sequence at the end of chromosomes that protects from loss during replication and shortens over time

telomerase

enzyme that prevents telomere shortening in stem and germ cells, lengthening the template strand

transcription

process in which dna is transcribed into rna with 3 stages

steps involve protein dna interactions

initiation

first step of transcription

elongation

second step of transcription

termination

third/final step of transcription

mRNA

messenger rna - encodes proteins

tRNA

transfer RNA, adapter between mRNA and amino acids during translation

rRNA

ribosomal RNA, enzymatic component of the ribosome

promoters

dna sequences that promote gene expression during initiation of transcription, directing location for it

located upstream of site where transcription of gene begins

ingredients for transcription

core promoter/tata box, general transcription factors, and RNA polymerase II

core promoter/TATA box

short dna sequence necessary for transcription to take place

generic transcription factors

proteins that sequentially bind to core promoter that allows basal transcription

RNA polymerase II

enzyme that transcribes mRNA

proximal promoter sequences

GC boxes and CAAT box

presence is gene dependent and has binding sites for transcription factor proteins

regulatory transcription factors

proteins that activate or repress the transcription of specific genes

bind to enhancer or silencer DNA regions