The mitotic cell cycle Flashcards

Question

Outline briefly how a tumour forms (2)

Answer 1

uncontrolled mitosis leads to no contact inhibition (cells continue to grow when they contact other cells), cell cycle checkpoints not controlled. abnormal mass of cells formed, cells do not function (as tissue of origin)

Answer 2

change in base sequence of DNA which leads to change in amino acid sequence of polypeptide/ protein

Answer 3

cell cycle shorter/ interphase shorter/ division more frequent (cell cycle) checkpoints not controlled ; uncontrolled (growth/division)/AW

Answer 4

Interphase is the stage between cell divisions and has three phases: G1 phase: Cell grows, makes RNA, enzymes, and proteins. Cell decides whether to divide. S phase (Synthesis): DNA replicates, forming chromosomes with two identical chromatids. G2 phase: Cell continues to grow; new DNA is checked and errors repaired. Proteins like tubulin are made to prepare for mitosis.

Answer 5

M phase (mitosis). Cell growth stops during this time

Answer 6

After the M phase, when the nucleus has divided into two, the whole cell divides to create two genetically identical cells. In animal cells, cell division involves constriction of the cytoplasm between the two new nuclei, a process called cytokinesis. In plant cells, it involves the formation of a new cell wall between the two new nuclei.

Answer 7

During late prophase. It doesn't disappear in fact, it breaks up into small vesicles which cannot be seen with a light microscope. Then it reassembles during telophase.

Answer 8

- plant cells do not contain centrosomes - after nuclear division of a plant cell, a new cell wall must form between the daughter nuclei

Answer 9

Cytokinesis is when the cell divides by constriction of the cytoplasm. As the shape of the cell changes the surface area increases which creates 2 new cells meaning new cell surface membrane has to be made

Answer 10

chromosomes start to appear as the chromatin coils up, becoming shorter and thicker; they are thick enough to become visible when stained. There are two centrosomes produced by the replication of original centrosome during S phase Features: nucleolus, intact nuclear envelope, cytoplasm, cell surface membrane, centrosomes, centromere with attached kinetochores (protein structures where spindle fibres attach)

Answer 11

the main microtubule organising centre in animal cells

Answer 12

one of two small, cylindrical structures, made from microtubules, Location: outside the nucleus in animal cells, in a region known as the centrosome, they are also found at the bases of cilia and flagella

Answer 13

nuclear envelope ‘disappears’ (it breaks up into small vesicles which are not visible with a light microscope), nucleolus ‘disappears’ (forms part of several chromosomes), chromosomes are seen to consist of two identical chromatids (each chromatid contains one DNA molecule), centrosomes moving to opposite ends of nucleus where they form the poles of the spindle (at the end a spindle is formed)

Answer 14

Each centrosome reaches a pole; centrosomes help to organise production of the spindle microtubules, chromosomes line up across the equator of the spindle; they are attached by their centromeres to the spindle Features: spindle fibres, centrioles, chromosomes, cell surface membrane

Answer 15

each chromosome splits at the centromere and the chromatids get pulled apart by microtubules by shortening spindle fibres chromatids move to opposite poles of the cell, centromeres first, pulled by the microtubules

Answer 16

nuclear envelope and nucleolus reforms again, chromatids have reached the poles of the spindle they will now uncoil again (each chromatid contains one DNA molecule, which will replicate itself during interphase before the next division), centrosome – will replicate during interphase before the next nuclear division, spindle fibres are broken down. A cleavage furrow (indentation of cell surface membrane) is formed before cytokinesis

Answer 17

a protein structure found at the centromere of a chromatid to which microtubules attach during nuclear division

Answer 18

1. DNA double helix unwinds 2. Hydrogen bonds between complementary nucleotide bases break which is catalysed by DNA helicase 3. Each strand acts as a template for the formation of new strands 4. Free activated nucleotides in the nucleus pair with the exposed bases on each template strand using complementary base pairing 5. The enzyme DNA polymerase catalyses the addition of the new nucleotide bases in the 5' to 3' direction 6. On the leading strand, DNA polymerase moves continuously towards the replication fork, adding nucleotides in a smooth, uninterrupted fashion while on the lagging strand, DNA is made in short sections called Okazaki fragments, which are later joined by DNA ligase 7. Replication proceeds step-by-step along the entire DNA molecule, and the result is semi-conservative replication, where each new DNA molecule contains one original and one newly synthesised strand

Answer 19

The mRNA for macrophage elastase binds to a ribosome in the cytoplasm, where translation begins at the start codon, typically AUG. A tRNA molecule carrying the corresponding amino acid (methionine) binds to this start codon through complementary base pairing between its anticodon and the mRNA codon. More tRNA molecules, each with a specific anticodon and amino acid, arrive at the ribosome. As two tRNAs occupy the ribosome at once, their amino acids are positioned side by side and joined by a peptide bond, catalysed by peptidyl transferase. The ribosome then moves along the mRNA in the 5’ to 3’ direction, allowing new tRNAs to enter and bring additional amino acids one at a time. This process continues, building the polypeptide chain of macrophage elastase, until a stop codon is reached. At this point, the completed protein is released, ready to fold and function.

Answer 20

During polypeptide synthesis, tRNA plays a crucial role by carrying specific amino acids to the ribosome. Each tRNA molecule is attached to a particular amino acid, ensuring the correct primary structure of the protein. The tRNA has an anticodon that binds to a complementary codon on the mRNA strand through base pairing (e.g., A-U, C-G). Within the ribosome, tRNA molecules bind at specific sites, and typically, two tRNAs are bound at the same time. This positions their amino acids close together, allowing a peptide bond to form between them. Once its amino acid has been added to the chain, the tRNA is released and can be reused to carry another amino acid.

Answer 21

Telomeres are repetitive, non-coding sequences of DNA found at the ends of chromosomes. During DNA replication, the very ends of DNA cannot be fully copied by DNA polymerase. Telomeres act as protective caps, so the loss occurs in these non-coding regions rather than in essential genes. - This prevents the loss of genetic material, maintaining genome stability. - permits continued replication - length of telomere determines lifespan of cells

Answer 22

a relatively unspecialised cell that retains the ability to divide an unlimited number of times, and which has the potential to become a specialised cell

Answer 23

During mitosis, centrioles help organise the formation of the spindle fibres. These spindle fibres are essential for separating sister chromatids by attaching to their centromeres and pulling them to opposite poles of the cell.

Answer 24

It forms part of spindle fibres which attach to centromeres and shorten during anaphase to split sister chromatids to opposite poles

Answer 25

It disassembles and breaks down into vesicles in prophase but at telophase it is reformed

Answer 26

attaches to centromeres during prophase to arrange the chromosomes on the equator and pull chromosomes apart to the poles of the cell. It is also attached to centrioles

Answer 27

It forms a cleavage furrow so that cell can be divided into 2

Answer 28

Totipotent- totipotent stem cells are stem cells that can differentiate into any cell type found in an embryo, as well as extra-embryonic cells (the cells that make up the placenta) Pluripotent- pluripotent stem cells are embryonic stem cells that can differentiate into any cell type found in an embryo but are not able to differentiate into extra-embryonic cells Multipotent- multipotent stem cells are adult stem cells that have lost some of the potency associated with embryonic stem cells and are no longer pluripotent (they have already partially differentiated)

Answer 29

In cell replacement and tissue repair, stem cells divide to replace damaged, old, or lost cells, helping to maintain and restore the structure and function of tissues throughout the body. Although these adult stem cells can divide (by mitosis) an unlimited number of times, they are only able to produce a limited range of cell types

Answer 30

Purines are bases with double ring structure Adenine, guanine

Answer 31

Bases with a single ring structure Thymine, uracil, cytosine

Answer 32

the strand of a DNA molecule that is used in transcription is called the transcribed or template strand and that the other strand is called the non-transcribed strand

Answer 33

a change in the sequence of base pairs in a DNA molecule that may result in an altered polypeptide

Answer 34

involved in translation as it provides a binding site for mRNA and the binding site for 2 tRNA molecules, it holds two amino acids close together and forms peptide bonds

Answer 35

Early cell death or the cell being destroyed by the body’s immune system

Answer 36

Uncontrolled cell division occurs when regulatory mechanisms fail, often due to mutations in genes that control the cell cycle. Cells divide rapidly and continuously without the usual signals to stop. This leads to a mass of abnormal cells, known as a tumour. If the tumour invades surrounding tissues or spreads, it can become cancerous.

Answer 37

any agents that may cause cancer

Answer 38

A tumour forms when cells divide uncontrollably due to mutations in genes that regulate the cell cycle. If the tumour is malignant, it can invade surrounding tissues and spread to other parts of the body through the blood or lymphatic system — a process called metastasis. This uncontrolled growth and spread of abnormal cells disrupts normal body functions and leads to cancer.

Answer 39

- A nitrogen-containing base (also known as a nitrogenous base) - A pentose sugar (containing 5 carbon atoms) - A phosphate group

Answer 40

- adenine - ribose sugar (these combined are known as adenosine) - phosphate groups (ATP has 3, ADP has 2, AMP has 1)

Answer 41

a bond joining two nucleotides together; there are two ester bonds, one from the shared phosphate group to each of the sugars either side of it

Answer 42

A DNA molecule consists of two antiparallel strands running in opposite directions — one in the 5′ to 3′ direction and the other in the 3′ to 5′ direction. These strands are twisted into a double helix. Each strand is made up of nucleotides joined together by phosphodiester bonds between the deoxyribose sugar of one nucleotide and the phosphate group of the next. The two strands are held together by complementary base pairing, where adenine (A) pairs with thymine (T) using two hydrogen bonds, and cytosine (C) pairs with guanine (G) using three hydrogen bonds. The complementary and antiparallel arrangement ensures accurate replication and stability of the DNA structure.

Answer 43

gene is a sequence of nucleotides that forms part of a DNA molecule

Answer 44

copying the genetic information in a molecule of DNA into a complementary strand of mRNA; a single strand of the DNA is used as a template (this is called the template or transcribed strand) – the enzyme responsible is RNA polymerase

Answer 45

a stage in protein synthesis during which a sequence of nucleotides in a molecule of messenger RNA (mRNA) is converted (translated) into a corresponding sequence of amino acids in a polypeptide chain. It takes place at ribosomes

Answer 46

DNA and RNA are both nucleic acids made of nucleotides, but they differ in several key ways. DNA is double-stranded, forming a double helix, while RNA is single-stranded. The sugar in DNA is deoxyribose, whereas RNA contains ribose, which has one more oxygen atom. DNA has the bases adenine, cytosine, guanine, and thymine, while RNA uses uracil in place of thymine. DNA is typically longer and more stable, storing the entire genetic code in the nucleus. In contrast, RNA is short-lived and acts as a messenger or helper, carrying genetic information (as mRNA), bringing amino acids (as tRNA), or forming part of the ribosome (as rRNA). While DNA remains mostly in the nucleus, RNA works mainly in the cytoplasm.

Answer 47

The universal genetic code is based on sequences of three DNA bases, called triplets or codons, each of which codes for a specific amino acid or signals the start or stop of protein synthesis (These signals tell the cell where individual genes start and stop which ensures the cell reads the DNA correctly and can produce the correct sequences of amino acids). During transcription and translation, these codons are read in sets of three. The genetic code is described as universal because the same codons specify the same amino acids in almost all living organisms, from bacteria to humans. In addition, the genetic code is degenerate, meaning that more than one triplet can code for the same amino acid, which helps reduce the impact of mutations. (64 codons, 20 amino acids

Answer 48

This stage of protein synthesis occurs in the nucleus of the cell 1. RNA polymerase attaches to the beginning of the gene to be copied. It starts to unwind the DNA of the gene and another enzyme breaks the hydrogen bonds between the two strands 2. Free activated RNA nucleotides in the nucleus pair with their complementary DNA bases on the template strand 3. The enzyme RNA polymerase links the RNA nucleotides together by forming phosphodiester bonds between their sugar and phosphate groups. This forms the sugar-phosphate backbone of the new messenger RNA (mRNA) strand 4. Once the entire gene has been transcribed, the mRNA strand is complete. The hydrogen bonds between the mRNA and DNA break, and the DNA strands re-zip to form the double helix again 5. The newly formed mRNA, which contains codons (groups of three bases), exits the nucleus through a nuclear pore in the nuclear envelope

Answer 49

1. In the cytoplasm the mRNA attaches to a ribosome 2. Each tRNA has the complementary anticodon to the codon on mRNA 3. The tRNA with the anticodon complementary to the first codon on the mRNA enters the ribosome and attaches to the codon by hydrogen bonding. This carries the first amino acid. 4. Two tRNA molecules can fit into the ribosome at any one time, so the second tRNA enters the ribosome. This has the anticodon which matches the second codon in the mRNA 5. A peptide bond forms between the two amino acids which are now side by side 6. The ribosome moves along the mRNA in a 5' to 3' direction 7. The first tRNA now leaves, the ribosome moves forward one codon and the third tRNA enters, carrying the next amino acid 8. This continues until a stop codon is reached

Answer 50

DNA polymerase is the enzyme involved in DNA replication; RNA polymerase is the enzyme involved in transcription

Answer 51

Involved in transcription Binding to the DNA RNA polymerase binds to a specific region at the start of a gene called the promoter on the DNA template strand. Unwinding the DNA It helps separate the DNA strands, exposing the template strand so that it can be read. Synthesising the mRNA Strand RNA polymerase reads the DNA template strand and matches complementary RNA nucleotides to each DNA base: Forming the Sugar-Phosphate Backbone It joins the RNA nucleotides together by creating phosphodiester bonds, forming the backbone of the mRNA molecule. Terminating Transcription RNA polymerase continues until it reaches a terminator sequence, where it stops transcribing and releases the mRNA.

Answer 52

Carries the Genetic Code - mRNA is transcribed from DNA in the nucleus during transcription. It carries the genetic instructions (as a sequence of codons) from a gene to the ribosome, where proteins are made. Contains Codons - The codons (triplets of RNA bases) on the mRNA specify which amino acids will be added to the polypeptide chain and in what order. Directs Translation - During translation, ribosomes read the codons on the mRNA. Each codon on the mRNA matches with a complementary anticodon on a tRNA molecule that brings the correct amino acid. Determines the Start and End of Protein Synthesis - The start codon (AUG) on mRNA signals the beginning of translation. Stop codons (UAA, UAG, UGA) signal the end of the polypeptide chain.

Answer 53

Code for Specific Amino Acids - Each codon corresponds to one specific amino acid. This ensures that the amino acids are assembled in the correct order to form a functioning protein. Determine Start and Stop Points - The start codon (AUG) signals the beginning of translation and sets the reading frame. - Stop codons (UAA, UAG, UGA) signal the end of translation, telling the ribosome to release the completed polypeptide. Guide tRNA Binding - Each codon on mRNA is matched by a complementary anticodon on a tRNA molecule. - This ensures that the correct amino acid is brought into place during protein synthesis

Answer 54

Ensure Correct Amino Acid Delivery - Each anticodon pairs with a specific mRNA codon through complementary base pairing. This pairing ensures the correct tRNA, carrying the correct amino acid, is used. Maintain the Reading Frame - The codon–anticodon interaction helps the ribosome move in a three-base step, maintaining the correct reading frame. Link Genetic Code to Amino Acids - Anticodons are the physical bridge between the mRNA sequence and the amino acid being added to the polypeptide chain.

Answer 55

In eukaryotic cells, the initial RNA molecule produced after transcription is called the primary transcript or pre-mRNA. This molecule contains both exons, which are coding sequences, and introns, which are non-coding sequences. Before the RNA can be used in translation, it must be processed. This involves removing the introns in a process called splicing. The remaining exons are then fused together to form a continuous sequence that codes for a polypeptide. The resulting, shorter molecule is called mature mRNA, which is then transported out of the nucleus to the ribosome, where it is used during translation to synthesise a protein

Answer 56

substitution – a base is replaced by a different base deletion – a base is lost and not replaced insertion – a base is added.

Answer 57

a type of gene mutation caused by insertion or deletion of one or more nucleotides, resulting in incorrect reading of the sequence of triplets in the genetic code due to a shift in the reading frame

Answer 58

Substitution mutation that occurs when a base in the DNA sequence is randomly swapped for a different base. Unlike an insertion or deletion mutation, a substitution mutation will only change the amino acid for the triplet (a group of three bases) in which the mutation occurs; it will not have a knock-on effect Substitution mutations can take three forms: Silent mutations – the mutation does not alter the amino acid sequence of the polypeptide (This is because certain codons may code for the same amino acid as the genetic code is degenerate) Missense mutations – the mutation alters a single amino acid in the polypeptide chain Nonsense mutations – the mutation creates a premature stop codon (signal for the cell to stop translation of the mRNA molecule into an amino acid sequence), causing the polypeptide chain produced to be incomplete and therefore affecting the final protein structure and function

Answer 59

A deletion mutation changes the amino acid that would have been coded for by the original base triplet, as it creates a new, different triplet of bases. A deletion mutation also has a knock-on effect by changing the triplets (groups of three bases) further on in the DNA sequence. This may dramatically change the amino acid sequence produced from this gene and therefore the ability of the polypeptide to function (could also cause a premature stop)

Answer 60

An insertion mutation changes the amino acid that would have been coded for by the original base triplet, as it creates a new, different triplet of bases. An insertion mutation also has a knock-on effect by changing the triplets (groups of three bases) further on in the DNA sequence. This may dramatically change the amino acid sequence produced from this gene and therefore the ability of the polypeptide to function (could also cause a premature stop)

The mitotic cell cycle Flashcards

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