Inheritance-preservation of genetic code

Question 1

Cell cycle (phases)

Answer 1

interphase makes up 90% the cycle
mitotic phase is 10%

Question 2

interphase

Answer 2

G1 phase: the cell grows

S phase: the chromosomes are duplicated through DNA replication

G2 phase: the cells continue to grow and prepare for mitosis

G0 phase: the cell is not in a cycle and perform its job in the organism without replication

Question 3

mitotic phase

Answer 3

Mitosis: prophase, prometaphase, metaphase, anaphase and telophase. distributes the daughter chromosomes to daughter nuclei

Cytokinesis: division of the cytoplasm forming two daughter cells

Question 4

(1) prophase

Answer 4

Chromatin fibres condense into discrete chromosomes, appearing as two sister chromatids joined at the centrosome

Nucleoli (structure within nucleus which produces ribosomes) disappear

The mitotic spindle begins to form: centrosomes move away from each other as the microtubules between them lengthen

Question 5

(2) prometaphase

Answer 5

The nuclear envelope fragments

The chromosomes condense even more and form a kinetochore (specialized protein structure) at each centromere (2 per chromosome). Microtubules can attach to these kinetochores to jerk the chromosomes back and forth

Question 6

(3) metaphase

Answer 6

The centrosomes are now at opposite poles of the cell

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

Microtubules are attached to both kinetochores of each chromosome

Question 7

(4) anaphase

Answer 7

The cohesin proteins holding chromatids together are cleaved, causing the chromatids to separate into 2 independent chromosomes

The separate chromosomes move to opposite ends of the cell, pulled by microtubules. Meanwhile, other microtubules cause the cell to keep lengthening

Question 8

(5) telophase

Answer 8

2 daughter nuclei form from the fragments of the previous nuclear envelope, and nucleoli reappear

The chromosomes become less condensed and spindle microtubules depolymerize

The cytoplasm divides into 2 daughter cells. In animal cells, the cytokinesis begins with a cleavage furrow (groove in the cell surface); this is mediated by the proteins actin and myosin, which cause the cell centre to contract. In plant cells, vesicles carrying cell wall materials form a cell plate in the middle of a plate

Question 9

MCM protein

Answer 9

family of proteins that bind to the replication origin and ORC proteins

Question 10

ORC proteins

Answer 10

origin replication complex protein where the MCM protein binds to

Question 11

restriction of DNA replication

Answer 11

replication can only occur when MCM proteins are bound.
Once initiation has occurred, the MCM proteins are displaced from the origin, so replication cannot initiate again until the cell passes through mitosis and enters the G1 phase of the next cell cycle

Question 12

regulatory molecule (steps)

Answer 12

mainly protein kinases and cyclins pace the sequential events of the cycle

1) synthesis of cyclin begins late S phase and all G2 phases (protected from degradation)

2) Cyclin with Cdk produces MPF molecules, which accumulate and let the cell to pass the G2 checkpoint to begin mitosis

3) MPF promotes mitosis by phosphorylating proteins. MPF peak during metaphase

4) cyclin and MPF is degraded during anaphase ending the M phase. Cell enters G1 phase

5) in G1, cyclin is degraded and Cdk is recycled for the next cycle

Question 13

Cdk

Answer 13

cyclin-dependent kinases, kinases can only be activated when bounded by cyclin

Question 14

MPF

Answer 14

when cyclin binds with Cdk, creates a complex called MPF

Question 15

kinases

Answer 15

enzymes that activate or inactivate other proteins by phosphorylating them

Question 16

Checkpoint

Answer 16

G1: if not check goes into G0 phase
S: stops in DNA damages
G2: at the end of the phase just before mitosis
M: to begin anaphase and between anaphase and telophase to ensure that anaphase is completed

Question 17

P53 protein

Answer 17

• It can activate DNA repair proteins when DNA has sustained damage
• If it recognises DNA damage, it can halt cell growth by holding the cell cycle at the G1 or S checkpoint on DNA damage recognition
• It can initiate apoptosis (i.e., programmed cell death) if DNA damage proves to be irreparable

Question 18

meiosis

Answer 18

division of sexual cells resulting in 2 times less chromosomes.
interphase, Meiosis 1, and Meiosis 2

Question 19

interphase

Answer 19

DNA is replicated, resulting in pairs of duplicated homologous chromosomes

Question 20

Meiosis 1

Answer 20

the homologous chromosomes separate, with each one going into a different daughter cell

Question 21

Meiosis 2

Answer 21

the sister chromatids separate

Question 22

(1) prophase 1

Answer 22

Crossing over occurs. Pairs of homologous chromosomes are joined together through chiasmata (regions where crossovers occurred)

Nuclear envelope breaks down

Centrosomes move apart, forming spindles between them

Microtubules attach to the kinetochores on the centrosomes of each chromosome in a homologous pair

Question 23

(2) metaphase 1

Answer 23

Pairs of homologous chromosomes are arranged

Question 24

(3) anaphase 1

Answer 24

The proteins holding the chromosome pairs together break down, allowing the homologs to separate

Each homolog moves to an opposite pole, guided by the spindle apparatus

Question 25

(4) telophase 1 and cytokinesis

Answer 25

two haploid daughter cells are formed through cytokinesis

Question 26

(1) prophase 2

Answer 26

The spindle apparatus forms

Question 27

(2) metaphase 2

Answer 27

Chromosomes are positioned at the metaphase plate

Microtubules from opposite poles attach at the kinetochores of each chromatid

Question 28

(3) anaphase 2

Answer 28

The proteins holding the sister chromatids together break down

The chromatids separate and move to opposite poles

Question 29

(4) telophase 2 and cytokinesis

Answer 29

Nuclei form and the chromosomes begin decondensing. Cytokinesis occurs

Question 30

crossing over (prophase 1) (steps)

Answer 30

1) Each gene on one homolog is aligned precisely with the corresponding allele of that gene on the other homolog.
The DNA of two non-sister chromatids is broken in precisely matching spots

2) A zipper-like structure called the synaptonemal complex holds the two homologs closely together. This is called synopsis

3) The broken ends of DNA are joined to the corresponding segments of non-sister chromatids

4) The synaptonemal complex disassembles, but homologs remain joined together in the points where crossing over happens. These points are called chiasmata

Question 31

incomplete dominance

Answer 31

red and white flowers can breed into pink flowers

Question 32

codominant

Answer 32

where both phenotypes are equally present (e.g. blood type AB)

Question 33

pleiotropy

Answer 33

several phenotypic effects, For example, the gene that determines flower colour also affects the colour of the coating on the outer surface of the seed

Question 34

epistasis

Answer 34

Phenotypic expression can depend on more than one gene

Environmental conditions can have an impact on phenotypic expression

Question 35

polygenic inheritance

Answer 35

two or more genes have an additive effect on a single phenotypic character. For example, height depends on more than 180 genes

Question 36

alleles

Answer 36

Alternative versions of genes account for variations in inherited characters

Question 37

heterozygous

Answer 37

gene that has opposite alleles

Question 38

homozygous

Answer 38

gene that has identical alleles