The cell cycle and mitosis and cellular organisation Module 2 Flashcards
Describe the cell cycle briefly?
Order:
Cell division:
M phase - Mitosis and cytokenesis
Interphase: cell growth and reproduction
G1 G1 checkpoint S G2 checkpoint
What occurs at G1 checkpoint and G2 checkpoint?
G1 checkpoint: Cell checks that the chemicals required for replication are present, and for any DNA damage before entering the s Phase G2 checkpoint: The cell checks if all the DNA has been replicated without damage, to see if it can enter the M phase
The 6 steps in cell division?
Interphase Prophase (Mitosis) Metaphase (Mitosis) Anaphase (Mitosis) Telophase (Mitosis) Cytokenesis
What occurs during interphase?
The cell carries out normal functions, but also prepares to divide Cell’s DNA is replicated, to double it’s genetic content, the organelles are also replicated so it has spare ones ATP content is increased (provides energy for cell division)
What’s a chromosome, a chromatid, sister chromatids, homologous pairs and a centromere?
A chromosome is half the X before replication in interphase, and is the whole X shape after replication A chromatid is the part of the X which would be there before replication SIster chromatids, and the bottom or top 2 parts of the X paired up Homologous pairs are when there’s 1 chromosome from the mum and 1 from the dad, they have the same genes in the same order, but will have different allels Centromere joins the 2 strands of the chromosome in the middle
Describe what occurs in the first step of mitosis, prophase?
Chromosomes condense Centrioles start moving to opposite ends of the cell, forming a network of protein fibres across it called spindle Nuclear envelope breaks down and chromosomes lie free in the cytoplasm
What occurs in the second step of mitosis, metaphase?
The chromosomes line up along the middle of the cell (laying sideways), and become attached to the spindle by their centromers Metaphase checkpoint, checks to see that all chromosomes are attached to the spindle before it can continue
What occurs in anaphase, the 3rd of mitosis?
Centromers divide Separating each pair of sister chromatids, the spindles contract pulling the chromatids to the opposite ends of the cell
What occurs in telophase, the 4th step of mitosis?
The chromatids reach the opposite poles of the spindle, and uncoil becoming long and thin again, so they’re now called chromosomes again A nuclear envelope forms around each group of chromosomes so there are now 2 nuclei Cytokenesis occurs next 9 (not part of mitosis)
Describe cytokenesis in mitosis?
The cytoplasm divides, a cleavage furrow forms to divide the cell membrane Produces 2 daughter cells which are genetically identical to each other and the original cell
Uses of mitosis?
Need for growth of multicellular organisms Repairing damaged tissue Method of asexual reproduction
What occurs in sexual reproduction?
2 gametes (an egg and a sperm), join together at fertilisation to form a zygote
Where does meiosis occur?
Occurs in sexual reproductive organs to produce gametes
What’s a gamete and what type of cell are they?
Produced in sexual reproductive organs, and contain half the amount of chromosomes of a normal cell, so they are haploid cells, and are all gentically different to each other as contain different combinations of chromosomes
How many chromosomes do human cells have?
46, so 23 homologous pairs
What are the steps in meiosis?
Interphase (DNA replicated) Prophase 1 Metaphase 1 Anaphase 1 Telophase 1 Cytokenesis Prophase 2 Metaphase 2 Anaphase 2 Telophase 2 Cytokenesis
What occurs in prophase 1, the first step of meiosis?
(DNA has already been replicated in interphase) Chromosomes condense, and arrange themselves into homologous pairs Crossing over occurs Centrioles start moving to opposite ends of the cells, forming the spindle fibres Nuclear envelope breaks down
What occurs in metaphase 1, the second step of meiosis?
The homologous pairs line up across the centre of the cell, and attach to the spindle fibres by their centromers
What happens in anaphase 1, the third step of meiosis?
The spindles contract, separating the homologous pairs, one chromosome goes to each end of the cell
What occurs in telophase 1, the 4th step of meiosis?
Nuclear envelope forms around each group of chromosomes, and then cytokinesis occurs and 2 haploid daughter cells are produced (still double stranded)
What happens in meiosis 2?
All the same steps as mitosis Produces 4 genetically different haploid daughter cells (single stranded chromosomes) = gametes
Describe chromatids crossing over in Prophase 1?
Homologous pairs have come together and pair up, the chromatids twist around each other, and bits of chromatids swap over The chromosomes still contain the same genes, but have different alleles
2 ways meiosis creates cells which are genetically different?
Crossing over if the chromatids Independent assortment of chromosomes
Describe the independent assortment of chromosomes?
Each homologous pair of chromosomes in your cells is made up of one chromosome from your mum (maternal), and one from your dad (paternal) When the homologous pairs line up in metaphase 1, and are separated in anaphase 1, it’s random which chromosome from each pair ends up in which daughter cell So all 4 daughter cells have different combinations of maternal and paternal chromosomes
What are stem cells?
Unspecialised cells, that can develop into different types of cells
Where are stem cells most commonly found?
In human embryos
What’s the process of a stem cell dividing to become a new cell which then becomes specialised?
Differentiation
What do adult stem cells in the bone marrow differentiate into?
They divide and differentiate to replace worn out erythrocytes (red blood cells) and Nuetrophils (white blood cells)
In plants what do the stem cells in the meristems differentiate into?
Xylem vessels and phloem sieve tubes
Why could stem cells be used to cure nuerone disorders such as Alzheimers and parkinsons?
In Alzheimers nerve cells in the brain die in increasing numbers, resulting in memory loss. Stem cells could be used to regrow healthy nerve cells In parkinsons loss of nerve cell which produces dopamine for movement, can regrow these with nerve cells
How are nuetrophils (type of white blood cell) adapted to perform their function?
Their flexible shape allows, them to ingest foreign particles or pathogens. The lysosomes in their cytoplasm contain digestive enzymes to break down the engulfed particles
How are erythrocytes adapted to perform their function?
The bioconcave disc shape provides a large surface area for gas exchange They have no nucleus, so there’s more for haemoglobin
How are epithelial cells (cover the surfaces of organs) adapted to perform their function?
CIliated epithial cells (in the air ways) have cilia that beat to move particles away Squamous epithelial cells (in the lungs) are very thin to allow efficent diffusion of gases
How are sperm cells adapted to perform their function?
Have a flagellum so they can swim to the egg Have lots of mitochondrion to provide energy to swim The acrosome (head) contains digestive enzymes, that enable the sperm to penetrate the surface of the egg
How are palisade mesophyll cells in leaves adapted to perform their function?
They do most of the photosynthesis, so they contain many chloroplasts, so can absorb a lot of sunlight The walls are thin, so CO2 can easily into the cell
How are root hair cells adapted to their perform their function?
Absorb mineral ions from the soil, so have a large surface area for absorption, and a thin permeable cell wall for entry of water and ions The cytoplasm contains extra mitochondria to provide the energy required for active transport
How are guard cells adapted to perform their function?
Found in pairs with a gap between them to form a stoma, which is a tiny pore in the surface of the leaf used for gas exchange In the light, guard cells take up water and become turgid, forcing them open, and allowing gas exchange for photosynthesis
What’s a tissue?
A group of cells that are specialised to work together to perform a particular function
What does the tissue squamous epithelium do?
A single layer of flat cells lining a surface, found in the alveoli of the lungs
What does the tissue ciliated epithelium do?
Layer of cells covered in cilia, it’s found on the surfaces where things need to be moved, eg in the trachea to move mucus
What do muscle tissues do and what does it consist of?
Made up of muscle fibres, there are 3 types of muscle tissue, smooth (found in lining of stomach wall), cardiac (found in heart), and skeletal which is used to move
What does the tissue cartilage do?
Type of connective tissue found in the joints Formed when cells called chondrolasts secrete an extracellular matrix in which they become trapped in
What does xylem tissue do?
Transports water around the plant Supports the plant Contains dead hollow xylem vessel cells and living parenchyma cells
What’s an organ?
Group of different tissues that work together to perform a particular function Eg. the lungs and leaves
What’s an organ system?
Organs working together to perform a particular function, eg. respiratory system or circulatory system
What does phloem tissue do?
Transports sugars around the plant, arranged in tubes made up of sieve tube elements and companion cells
