Cell Cycle and Cancer 8.21

Question 1

Describe the nucleolus

Answer 1

ribosome factory located in the nucleus comprised of 10 chromosomes each expressing 40 rRNA genes - for a total of ~400 genes

Question 2

how are ribosomes made

Answer 2

RNA Polymerase I synthesizes rRNA transcripts of size 5.8s, 18s, and 28s RNA polymerase III synthesizes rRNA transcripts of size 5s 18s binds with ribonucleoproteins (RNPs) to form small subunits of size 40s 5.8s, 28s, and 5s bind with RNPs to form large subunits of size 60s subunits migrate through pores (active export) into the cytoplasm where they combine to form mature 80s ribosomes

Question 3

when are the nucleoli most prominent

Answer 3

visible during interphase (when the cell makes new ribosomes), not seen during mitosis

Question 4

Describe the internal nuclear matrix

Answer 4

makes up 98% of the nuclear matrix contains thousands of non-histone proteins that confer non-random order to chromatin

Question 5

Evidence for non-random order in the internal nuclear matrix

Answer 5

there are matrix proteins that are tissue-specific (activating different genes depending on need/function of the cell) chromosomes occupy specific locations in the nucleus the matrix gives order to replication and transcription of DNA

Question 6

how was it shown that chromosomes are nonrandomly situated in the nucleus

Answer 6

1885: Rabl: showed that plant cell chromosomes anchor in a predictable pattern in the nucleus (telomeres at one end and centromere are the other) 1982: burn hole on opposite sides of nucleus and repair with isotopic thymidine - observed that in later cell generations, repair location were in the same spots relative to the other nucleus contents Barr body (inactive X female chromosome) always located on the nuclear lamina Fluorescent in situ hybridization (FISH) - fluoresce individual chromosomes - showed that each chromosome stays in an assigned region of the nucleus but that it can migrate to different locations within that region

Question 7

how is it shown that the matrix is responsible for facilitating mRNA transcription

Answer 7

stripping DNA from matrix and inducing transcription still results in mRNA from DNA on the anchor points of the matrix

Question 8

how many cells are in the human body

Answer 8

roughly 10 trillion

Question 9

What options does the cell have at the G1 phase

Answer 9

senescence - the absence of proliferation - puts the cell in G0 differentiation - also puts the cell in G0 apoptosis - cell death proliferation - commence with cell cycle

Question 10

What happens during the S phase

Answer 10

DNA is replicated and histone proteins are produced to form chromatin

Question 11

What happens during the G2 phase

Answer 11

preparation for mitosis, the centrosome duplicates

Question 12

relative time duration for each phase of the cell cycle

Answer 12

S, G2 and M maintain constant durations G1 is variable

Question 13

what is interphase comprised of

Answer 13

G1, S, and G2

Question 14

What are the external factors that influence the cell-cycle

Answer 14

hormones, cytokines, and growth factors these are extracellular

Question 15

What are the activator growth factors

Answer 15

fibroblast growth factor (FGF), Insulin-like growth factor (IGF), Wnt