Cell Division Flashcards
What is uncoiled DNA called?
Chromatin
What is chromatin?
A ball of uncoiled DNA found in nucleus, before division
What occurs to chromatin when cells divide?
They coil into organized structures known as chromatids
What is a single chromatid also known as?
Single chromatid = single stranded chromones
How many chromosomes are in a somatic cell? What is a somatic cell?
A somatic cell is any cell apart from the gamete cells (sperm/eggs)
- Has 46 chromosomes, AKA diploid, 2n
How many chromosomes are found in the gamete cells?
23, AKA haploid, n
What is produced when DNA replicates?
Produces a double stranded chromosome, (two chromosomes), AKA sister chromatids
What are the 3 phases of the cell cycle + their purpose?
- Interphase- 90 % of cell cycle, growth/dna replication
- Mitosis- divide genetic material
- Cytokinesis- divide cytoplasm
What is the purpose of the cell cycle?
- Growth
- asexual reproduction
- tissue repair
What is interphase?
- 1st step, prepares cell for divison
- has 3 phases
G1- growth phase, makes new organelles, proteins, etc (translation and transcription occurs here)
S- synthesis- DNA replication, makes an extra copy of chromosome
G2- growth, last prep for cell division
What is mitosis?
Has 4 phases for dividing genetic material
- Prophase
- Metaphase
- Anaphase
- Telophase
What occurs in prophase?
- Chromatic coils to make chromatids (sister chromatids)
- Spindle fibers form
- centrioles move to poles of the cell
- nuclear membrane dissolves
What conjoins sister chromatids?
Centromere
What occurs in metaphase?
- Sister chromatids line up on equator of cell
- spindle fibers attach to centromeres
What occurs during anaphase?
- Spindle fibers and centrioles pull sister chromatids apart to opposite sides of cell
- (double stranded chromosomes turn back into single stranded chromosome cells)
What occurs in telophase?
- Chromatids relax back into chromatin
- nuclear membrane reforms
- cell membrane begins to develop
(cleavage begins)
What is Cytokenesis?
- 3rd phase of cell division
- separation of cytoplasm
- begins in anaphase, continues through telophase, and completes at end or mitosis
What is left at the end of the cell division process?
Two identical daughter cells w/ chromatins
What does ploidy mean?
The number of sets of chromosomes in a cell ie: Chromosome 21 has pair or single chromosome?
What is a diploid?
Each chromosome has a pair, ie: 23 pairs, 46 chromosomes
Somatic cells= every cell in the body apart from gametes are 2n
What is haploid?
When a chromosome is single, and has no pairs
1 of each chromosome due to meiosis,
23 chromosomes= n
What is meiosis?
The process that makes gamete/sex cells ie: oogenesis/ spermatagenosis
Why is meiosis important?
- reduces the ploidy (number of sets) 2n-n in order for the zygote to only have 46 chromosomes
-
How many times does the cell divide in meiosis?
There are 2 divisions that occur, but only one DNA replication
What is a homologous pair?
-Paired chromosomes that are the same length, genes, and in the same order (one from mom, one from dad)
What is the process of synapsis?
When replicated homologous chromosomes form a tetrad (See diagrams)
tetrad: homologous chromosomes that have been replicated, so 4 chromatids are together
What is the process of crossing over?
- The breaking and rejoining of homologous chromosomes, genetic info meshes together
- increases genetic variation, all chromatids are different from each other
What are the steps to meiosis?
- interphase
- Meiosis I
- prophase 1
- metaphase 1
- anaphase 1
- telophase 1 - cytokinesis 1
- meiosis 2
- prophase 2
- metaphase 2
- anaphase 2
- telophase 2 - cytokinesis
What occurs during interphase of meiosis?
- DNA replicates, cell grows
- This only occurs ONCE during meiosis, before meiosis I
What is a non recombinant chromosome?
The part of the chromosome that has not exchanged genetic information
What occurs during prophase 1?
-chromatin condenses to chromatids, connects via centromere (starts with 46 chromosomes)
- nuclear membrane dissolves, spindle fibers form, centrioles to poles
- replicated homologous chromosomes pair up to form a tetrad
- “crossing over” occurs (exchange genetic info)
What is a tetrad?
homologous chromosomes that have been replicated that pair up with another = 2 chromosomes, 4 chromatids
What is metaphase 1?
- tetrads line up together on the equatorial plate
- spindle fibers attach to centromeres
What is anaphase 1?
- Homologous chromosomes is pulled apart
- diploid -> haploid
What is telophase 1?
- nuclear membrane reforms
- chromatids relax into chromosomes
- cleavage begins
What is cytokinesis 1?
- cleavage begins
- 2 daughter cells = haploid double stranded chromosomes
- not genetically identical
What occurs in meiosis 2, prophase 2?
- Chromatin=chromatids
- nuclear membrane dissolving
What occurs in metaphase 2?
- double stranded chromosomes line up on equatorial plate
- spindle fibers attach to centromeres
What occurs in anaphase 2?
-sister chromatids separate (doubles stranded chromosomes become single stranded chromosomes)
What occurs in telophase 2?
- chromatid = chromatin
- nuclear membrane reforms
- cleavage begins
What occurs in cytokinesis 2?
-cytoplasm finishes cleavage
- 4 genetically different daughter cells
(haploid- 23 chromosomes)
How does the formation of gametes occur?
Both occur using meiosis to make haploid gametes
What does spermatogenesis create?
- cell divides into two haploid cells which divide into 4 sperm cells
- equal distribution of cytoplasm between daughter cells
(quantity over quality)
How does oogenesis occur in terms of cell division?
- Primary oocyte divides into secondary oocyte and polar body, which divides into ovum and polar body, and the other polar body splits into 2 other polar bodies (3 polar bodies, 1 egg)
- unequal distribution of cytoplasm between daughter cells
- polar bodies eventually dissolve
(quality over quantity)
What is nondisjunction?
- abnormal meiosis
- occurs when homologous pairs or sister chromatids don’t separate properly during anaphase 1 or anaphase 2, respectively
What is a trisomy?
- one extra chromosomes
ex: trisomy 21 = extra chromosome 21 = down syndrome
What is a monosomy?
- one less chromosome (45)
ex: turners syndrome=one x chromosome only
Know diagrams for anaphase 1 and anaphase 2 nondisjunction
What is DNA made up of?
DNA is made up of nucleotides, which are composed of phosphate, deoxyribose sugars, and nitrogenous bases (purines/pyrimidines)
What does phosphate do in nucleotides?
Phosphates (po43) makes the DNA negatively charged
What do the nitrogenous bases do?
They keep the 2 strands of the dna together, held together by hydrogen bonds
What are the two types of nitrogenous bases?
Purines - Adenine and Guanine
Pyrimidines- Thymine and Cytosine
What forms the backbone of the DNA double helix? What bonds hold them?
Sugar phosphate backbone, which holds the nucleotides together
They are held together by phosphodiester bonds
In what direction are the backbones made?
- in the 5’ to 3’ direction,
- Travel anti parallel
What are the complementary bases on a DNA strand?
- A binds to T
- G binds to C
What are the differences of RNA from DNA?
Rna is:
- single stranded
- has ribose sugar
- Instead of T, A binds with U
- Not stored in the nucleus
Where does DNA replication occur?
This occurs in the nucleus
What does it mean to say that DNA replication is semi-conservative?
Each DNA molecule that has been replicated has one Og strand, and one new strand
What is the 1st step for DNA replication?
- DNA unwinds/unzips
- Enzyme helicase creates a replication fork by breaking hydrogen bonds between nitrogenous bases
What is the 2nd step for DNA replication?
- DNA polymerase binds exposed strand+ builds new strands in 5’ to 3’ direction
- Fork splits into leading strand and lagging strand
leading strand: built continuously (dna polymerase moves towards replication fork, built antiparallel)
lagging strand: made non continuously, dna polymerase moves away from replication fork
What is the 3rd step?
Dna polymerase proofreads + fixes any mutations
What is the 4th step for DNA replication?
DNA ligase connects phosphodiester bonds in backbone of fragments
During what phase does DNA replication occur?
The S phase on interphase
During what phase does transcription and translation occur?
During the G phases of interphase
Which two steps occur to create a polypeptide chain?
Transcription and transation
Where is and what occurs during transcription?
Occurs in the nucleus, purpose is to transcribe a gene in DNA onto an mRNA strand so it can leave the nucleus
What are the three steps to transcription?
a) initiation
b) Elongation
c) termination
What occurs during initiation of transcription?
-RNA polymerase binds to a promoter region ahead of gene to be transcribed (helicase assists to unzip and unwind)
What occurs during elongation phase of transcription?
- RNA polymerase builds on mRNA strand in 5’ to 3’ direction (Uses 3’ to 5’ as template)
- must be antiparallel but develop in the 5 to 3, so it uses to 3 to 5 as a template for complimentary bonds, however builds in the 5 to 3 direction
What occurs during the termination phase of transcription?
- RNA polymerase reaches ‘stop’ sequence in the proteins
- mRNA peels away and leaves nucleus
- mRNA polymerase falls off
- DNA rezips and rewinds
What is the difference between nucleotides in transcription and replication?
Replication= GCAT Transcription= GCAU
What are the three steps to translation?
Initiation, elongation, termination
What occurs during initiation?
- Ribosome binds at the start codon (AUG) on mRNA
- Brings in tRNA
What occurs during elongation?
- tRNA molecules will bind complementarily with codons on mRNA
- Amino acid on tRNA transfers to the growing polypeptide chain
- EMPTY tRNA leaves ribosome, new tRNA inds
What occurs during termination?
-Ribosome reaches STOP sequence/codon= ribosomes falls off, polypeptide released (mRNA is recycled)
What are the kinds of DNA technologies?
- Mitochondrial DNA
- cloning
- Gene therapy
- Recombinant DNA
- DNA finger printing
What is mitochondria DNA?
- inherited from maternal side (organelles+cytoplasm in zygote come from egg)
- little variation as there is no crossing over between DNA in the mitochondria
What is cloning?
- offspring is genetically identical to parent
- Nucleus of egg is removed, replaced with somatic (diploid) cell, zygote implanted, develops, birthed
What is gene therapy?
- Replacing defective genes with healthy ones
What is recombinant DNA?
- DNA molecule that has DNA fragments from multiple organisms
- Used to produce hormones, proteins, etc (outside of body ie: for production of insulin)
What is DNA finger printing?
-2 phases
- PCR - polymerase chain reaction
amplifies a section of DNA, makes many copies
Gel electrophoresis
- separate fragments of DNA based on size,
- DNA moves from negative terminal to positive terminal
