FHMP 005 chromosomes, genes and the cell cycle

Question 1

What is a chromosome?

Answer 1

a long continuous thread of DNA that consists of numerous genes

Question 2

What are homologous chromosomes?

Answer 2

Two genetically similar chromosomes, one from each parent

Question 3

What are sister chromatids?

Answer 3

2 identical copies of DNA held together by a centromere

Question 4

What is a diploid?

Answer 4

a cell that contains both sets of homologous chromosomes

Question 5

What is a haploid?

Answer 5

one set of chromosomes

Question 6

What is a karyotype?

Answer 6

the number and visual appearance of the chromosomes in the cell nuclei of an organism or species.

Question 7

how many autosomes and sex chromosomes does a human karyotype consist of?

Answer 7

• 44 autosomes (22 pairs) and 2 sex chromosomes (1 pair(

- in total 46 chromosomes and 23 pairs

Question 8

What is a karyogram? What does it show?

Answer 8

• A karyogram shows the chromosomes of an organism in homologous pairs;
• arranged in decreasing length;
• shows length and position of centromere of chromosomes;
• obtained by annealing each chromosome with a different colour fluorescent tag
• usually done during metaphase when more visible

Question 9

Describe the structure of DNA

Answer 9

• DNA is made up of molecules called nucleotides.
• Each nucleotide contains a phosphate group, a sugar group and a nitrogen base.
• The four types of nitrogen bases are adenine (A), thymine (T), guanine (G) and cytosine (C).
• A bind to T with 2 H bonds
• C binds to G with 3 bonds
• one strand runs 5’-3’ and the other runs antiparallel 3’ to 5’
• double helix has major and minor grooves for binding
• 3 bases on DNA codes for 1 amino acid
• wrapped around histone proteins
• have topoisomerases to untangle DNA

Question 10

What are the differences between DNA and RNA?

Answer 10

DNA: double-stranded, longer, has deoxyribose sugar, bases: A, T, G, C
RNA: single-stranded, shorter, has ribose sugar, bases: A, U, G, C

Question 11

What are the 3 domains?

Answer 11

Bacteria, Archaea, Eukarya

Question 12

What is a gene?

Answer 12

segment of DNA that codes for a protein

Question 13

What are introns and exons?

Answer 13

• introns are junk DNA- noncoding sequences.

- Exons are functional mRNA coding regions.

Question 14

What is a tandem repeat?

Answer 14

short sequences of nucleotides repeated (3-100 times) one after the other, usually in centromeres or telomeres or to separate genes

Question 15

What are telomeres?

Answer 15

• protective caps on the end of chromosomes, prevent fusing and deterioration
• 5-8bp repeat sequences
• telomerase maintains the telomere length
• telomere length shortens over time and is linked with age-related diseases

Question 16

What is X-inactivation?

Answer 16

• a process by which one of the two copies of the X chromosome present in female mammals is inactivated as only 1 is required for normal functioning
• is random and different in each cell and occurs during the blastocyst stage in embryo
• produces tortoise shell cats

Question 17

What are the phases of the cell cycle?

Answer 17

G1 (Go), S, G2, M

Question 18

Describe G1 phase

Answer 18

• cells do most growing here
• make new proteins and organelles
• can go into Go phase

Question 19

describe the Go phase

Answer 19

• “resting” state; cells function, but are not actively dividing (do not replicate DNA)
• “resting”: do not undergo DNA replication
• cell apoptosis and differentiation occurs

Question 20

Describe the S phase

Answer 20

• DNA replication occurs to form 2 sister chromatids

- DNA has doubled although the ploidy (sets of chromosomes) is the same

Question 21

Describe the G2 phase

Answer 21

• 2nd Growth Stage
• Occurs after DNA has been copied
• All cell structures needed for division are made (e.g. centrioles)
• Both organelles & proteins are synthesized

Question 22

Describe the M phase

Answer 22

• Cell division.
• Mitosis/Meiosis.
• Division of the genetic material.
• Prophase, metaphase, anaphase telophase, cytokinesis

Question 23

What is interphase?

Answer 23

G1, S, G2 ( phase between M stage)

Question 24

What are the checkpoints in the cell cycle?

Answer 24

• G1 checkpoint, G2 checkpoint, M checkpoint

- to regulate cell cycle, remove and repair DNA damage or mutations

Question 25

What is the G1 checkpoint?

Answer 25

releases cell to S phase if ready but G0 phase if not ( DNA not mutated, enough proteins, bases, enzymes…)

Question 26

what is the G2 checkpoint

Answer 26

check for no DNA damage/mutations, chromosome set complete, enough cell components for 2 daughter cells

Question 27

What is the M checkpoint?

Answer 27

Metaphase checkpoint that is monitored by proteins that can sense if a chromosome is not correctly attached to the spindle apparatus before anaphase

Question 28

What is mitochondrial DNA?

Answer 28

maternally inherited DNA in the mitochondria is transmitted only from mother to child (codes for mitochondrial proteins)

Question 29

What is a locus?

Answer 29

Location of a gene on a chromosome

Question 30

What is an allele?

Answer 30

Different forms of a gene

Question 31

what is homozygous and heterozygous?

Answer 31

Homozygous = two of the same allele (RR and rr) 
Heterozygous = one of each and two different alleles (Rr)