5 the mitotic cell cycle Flashcards
(25 cards)
enzymes [4]
helicase
primase
dna polymerase - add free nucleotides
dna ligase
📍helicase: separates the dna strands during replication
📍primase (recognise primers => use original template to synthesise new strand):
synthesises short segments of RNA
📍dna polymerase: removes RNA nucleotides from primer and adds eqivalent dna nucleotides to the 3’ end of okazaki fragments
📍dna ligase: covalently connects segments of dna
chromosomes
-CONDENSED dna
-coiled around histone proteins (structure support)
- one very long, condensed DNA molecule associated with proteins (in eukaryotic cells)
-main proteins: large, pos charge, globular proteins called HISTONES.
role of HISTONES: organise and condense the DNA tightly so that it fits into the nucleus
+other proteins: enzymes used in copying & repairing DNA
what is chromatin (DNA & proteins - dna coiled around histones to make chromatin)
tightly coiled combination of DNA and proteins
-what chromatids [one of 2 identical parts of a chromosome, formed during interphase by the replication of the DNA strand; made up of a series of genes] (and so chromosomes) are made of
DNA is…
-deoxyribonucleic acid
-genetic code
-genotype for phenotype
-instructions for protein production
-variations in human genome
keywords
+ bonding in DNA
-sugar-phosphate backbone
-hydrogen bond joining bases
-phosphodiester bonds between nucleotides
-NITROGENOUS bases make up nucleotides + sugar + phosphate
-“semi-conservative replication”
+nucleotides joined together via PHOSPHODIESTER BONDS
-phosphate joins with deoxyribose sugar.
-HYDROGEN bonds between BASES (weak but strong tgt)
-AT adenine + thymine
-GC guanine + cytosine
nucleotides to genes
nucleotides form SPECIFIC coding sequences (genes) => instructions for coding proteins & regulatory sequences + promoters.
Purines. AG
Pyrimidines CT [pyramidscheme]
general structure of a purine base:
-general structure of a pyrimidine base:
INTERPHASE (S phase)
what happens?
-DNA replicates
-to create 2 identical strands of DNA called chromatids
-joined together by a narrow region called the CENTROMERE
-2 chromatids that make up double structure of chromosome = SISTER chromatids
sister chromatids are…
which is important bc…
-sister chromatids are IDENTICAL (contain the same genes)
-to do w/ cell division ;;
-one chromatid goes into one daughter cell,
& one goes into the other daughter cell during MITOSIS, ensuring daughter cells are genetically IDENTICAL
-for GROWTH + repair.
📌telomeres
ends of chromatids (in chromosomes) are
“SEALED” with
PROTECTIVE STRUCTURES = telomere
“[extra] repetitive sequence of nucleotides/bases at end of chromosomes to protect ends ; [TTAGGG]x - does not contain active genes. TELOMERASE enzyme adds telomere sequence.” recognises end; elongates; adding additional repeats
telomeres function
-every DNA replication cycle causes shortening to ends of chromosomes; (shorten telmomeres instead of actual dna of genes)
-maintain chromosomal stability
-prevent chromosomal degradation
chromosome shortening (prevented by telomere)
-DNA at end of chromosome can’t be fully copied so gradual shortening of chromosome.
-each primer on lagging strand takes up small section of DNA sequence before polymerase can add new nucleotides.
when replication fork reaches the end, only enough space for primer but not new nucleotides.
antiparallel strands
-clockwise from oxygen
-phosphodiester bond from 3rd C to 4th C with phosphate
primes
5’ to 3’
-two strands in DNA run opposite direction to each other; due to angle of hydrogen bonds between complementary bases.
sum
- leading strand
- lagging
- continuous, normal adding of 5’ to 3’, ends go towards replication fork
- LAGGING: discontinuous add 5’ to 3’ in fragments (okazaki), fragments in the away direction of fork
dna replication
-happens BEFORE mitosis
-DNA copied before cell divides
-produces 2 IDENTICAL dna copies
(chromatids form chromosomes)
- semi-conservative DNA replication [each strand in dna double helix acts as template for new complementary strand;each copy contains 1 original strand & 1 new strand)
dna replication
- initiation
-unwind dna break H-bonds.
replication fork
two strands as templates
enzyme: helicase
- elongation
-starts by recognising primers (primase)
-using original template strand to synthesise new strand
-add free nucleotides, use enzyme DNA polymerase
-only in 5’ to 3’ direction
- termination
-stop at a terminator (specific sequence) or when replication forks meet
-2 new dna ladders.
-resumes double helix structure
describe how spindle is involved during mitosis [3]
-prophase attachment to centromere of each chromosome
-prophase arranging chromosomes at the metaphase plate
-anaphase centromere division/separation of sister chromatids
-anaphase pulling chromatids towards poles
cell death
- necrosis (uncontrolled “homicide”)
-cell loses functional control (toxins, injury)
-membrane destabilises and leads to swelling
-cell bursts and releases contents (causing inflammation)
- apoptosis (programmed “cell suicide”)
-controlled event
-triggered by mitochondrial proteins
-contents are packaged into blebs
-fragments into apoptotic bodies to be recycled.
tumors
-uncontrolled, unregulated mitosis (cell div)
-activate telomerase to prevent chromosomes becoming too short (&die)
-increase blood supply to maintain high demand for nutrients to keep up with high rate of cell division
-avoid immune system via cell/tissue communication
causes of tumor development
- mutagens/carcinogens
- genetics
- -agents that change genetic material of cells
eg physical agents (UV)
chemical (arsenic)
biological in origin (certain viruses for eg) - most cancers caused by mutations to:
-proto-oncogenes stimulate cell growth
-tumor suppressor that repress cell cycle progression.
assignment order steps
1-10
1 gyrase
2 unzip
3 replication fork
4 template, nucleotides move in
5 dna polymerase catalyses addition
6 hydrolysis
7 supplies energy for phosphodiester bonds
8 leading, cont
9 lagging, discont
10 okazaki frags joined catalysed by dna ligase
termination of process occurs when replication fork stops.
final product is 2 dna molecules, identical to each other + identical to parent dna molecules that initiated process.
- Catalyzed by a gyrase enzyme, the double helix begins to untwist a bit at a time and the DNA starts to unwind
- This allows the DNA molecule to start to unzip, where the hydrogen bonds between the complementary nucleotide bases break, and this is catalyzed by DNA helicase
- This unzipping action results in a structure known as the replication fork where the “branching” prongs contain single stranded DNA with exposed bases
- Using the single-stranded DNA as a template, free phosphorylated nucleotides move in and line up opposite the exposed bases according to complementary base-pairing rules
- The enzyme DNA polymerase catalyses the addition of the new nucleotide bases, in the 5’ to 3’ direction, to the single strands of DNA
- Hydrolysis of the activated nucleotides releases the extra phosphate groups
- This supplies the energy to form phosphodiester bonds between the deoxyribose sugar of one nucleotide and the phosphate group of the adjacent nucleotide
- As the leading strand is synthesised in the same direction as the growing replication fork, it can be replicated continuously
- As the direction of synthesis of the lagging strand is opposite to the direction of the growing replication fork, it is replicated discontinuously by forming short segments called Okazaki fragments
- The Okazaki fragments are joined during reactions catalyzed by DNA ligase
