FHMP 005 chromosomes, genes and the cell cycle Flashcards
What is a chromosome?
a long continuous thread of DNA that consists of numerous genes
What are homologous chromosomes?
Two genetically similar chromosomes, one from each parent
What are sister chromatids?
2 identical copies of DNA held together by a centromere
What is a diploid?
a cell that contains both sets of homologous chromosomes
What is a haploid?
one set of chromosomes
What is a karyotype?
the number and visual appearance of the chromosomes in the cell nuclei of an organism or species.
how many autosomes and sex chromosomes does a human karyotype consist of?
- 44 autosomes (22 pairs) and 2 sex chromosomes (1 pair(
- in total 46 chromosomes and 23 pairs
What is a karyogram? What does it show?
- 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
Describe the structure of DNA
- 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
What are the differences between DNA and RNA?
DNA: double-stranded, longer, has deoxyribose sugar, bases: A, T, G, C
RNA: single-stranded, shorter, has ribose sugar, bases: A, U, G, C
What are the 3 domains?
Bacteria, Archaea, Eukarya
What is a gene?
segment of DNA that codes for a protein
What are introns and exons?
- introns are junk DNA- noncoding sequences.
- Exons are functional mRNA coding regions.
What is a tandem repeat?
short sequences of nucleotides repeated (3-100 times) one after the other, usually in centromeres or telomeres or to separate genes
What are telomeres?
- 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
What is X-inactivation?
- 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
What are the phases of the cell cycle?
G1 (Go), S, G2, M
Describe G1 phase
- cells do most growing here
- make new proteins and organelles
- can go into Go phase
describe the Go phase
- “resting” state; cells function, but are not actively dividing (do not replicate DNA)
- “resting”: do not undergo DNA replication
- cell apoptosis and differentiation occurs
Describe the S phase
- DNA replication occurs to form 2 sister chromatids
- DNA has doubled although the ploidy (sets of chromosomes) is the same
Describe the G2 phase
- 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
Describe the M phase
- Cell division.
- Mitosis/Meiosis.
- Division of the genetic material.
- Prophase, metaphase, anaphase telophase, cytokinesis
What is interphase?
G1, S, G2 ( phase between M stage)
What are the checkpoints in the cell cycle?
- G1 checkpoint, G2 checkpoint, M checkpoint
- to regulate cell cycle, remove and repair DNA damage or mutations
