Cell Structure

Question 1

what does eukaryotic mean for the structure inside the cell

Answer 1

• a nucleus surrounded by a nuclear envelope in which DNA is contained and wound into linear chromosomes
• an area inside the nucleus called the nucleolus this contains RNA and is where the chromosomes unwind, it is also where ribosomes are made
• cytoplasm where the organelles are suspended
• a cytoskeleton - this is a network of protein filaments (actin or microtubules) within the cytoplasm that move organelles from place to place within the cell this allows cells such as amoebae and lymphocytes to move and allows contraction of muscle cells
• a plasma membrane - also called cell surface membrane or cytoplasmic membrane
• membrane bound organelles other than the nucleus such as mitochondria, the Golgi apparatus and endoplasmic reticulum
• small vesicles
• ribosomes which are organelles without membranes and where proteins are assembled

Question 2

What are organelles

Answer 2

these are the fundamental units and building blocks of all living organism
- each organelle has a specific function

Question 3

what is a membrane organelle and what types of cells do not have them

Answer 3

this means that the most of the organelles with in the eukaryotic cell is covered by a membrane - similar in structure to the plasma or cell surface membrane

• keeps organelle separate from the rest of the cell so that it is a discrete compartment
• prokaryotic cells do not have them

Question 4

What has enabled scientist to look at the structure of these organelles

Answer 4

electron microscopy

Question 5

what has enabled scientists to find the function of each organelle

Answer 5

biochemistry

Question 6

describe the structure of a nucleus, nuclear envelope and nucleolus

Answer 6

Nuclear envelope - this is surrounds the nucleus in a double envelope there are pores which allow substances to enter and leave
Nucleolus - this does not have a membrane around it and contains and makes RNA
Chromatin - this is the genetic material which consists of DNA wound around histone proteins when the cell is not dividing the chromatin is spread out or extended
when cell is about to divide chromatin condenses and coils tightly into chromosomes - make up all organisms genome

Question 7

Describe the function of the nucleus, nuclear envelope, nucleolus

Answer 7

• The nuclear envelope separates the contents of the nucleus from the rest of the cell
• in some regions the outer and inner nuclear membrane fuse together this means ribosomes and dissolved substances can pass through
• pores enable mRNA to leave the nucleus and some steroid hormones to enter the nucleus from the cytoplasm via the pores
• nucleolus - makes ribosomes
• chromosomes contain organisms genes

Question 8

What is the function of the nucleus in summary

Answer 8

• Control centre of the cell
• stores the organisms genome
• transmits the genetic information
• provides instructions for protein synthesis

Question 9

What is the structure of the RER

Answer 9

• this is a system of membranes containing fluid-filled cavities (cisternae) these are continuous with the nuclear membrane
• coated with ribosomes

Question 10

What is the function of the RER

Answer 10

• RER this is the intracellular transport system is when the cisternae form channels for transporting substances from one area of a cell to another
• provides a large surface area for ribosomes which assembled amino acids into proteins, proteins are then actively passed through the membrane into the cisternae and are transported to the Golgi apparatus for modification and packaging

Question 11

What is the structure of the SER

Answer 11

• a system containing fluid filled cavities cisternae that are continuous with the nuclear membrane
• there are no ribosomes on its surface

Question 12

What is the function of the SER

Answer 12

• contains enzymes that catalyse the reactions involved with lipid metabolism
• synthesis of cholesterol
• synthesis of lipids/phospholipids needed by the cell
• synthesis of steroid hormones
• involved with absorption, synthesis and transport of lipids from the gut

Question 13

What is the structure of the Golgi apparatus

Answer 13

• consists of a stack of membrane bound flattened sacs

- secretory vesicles bring materials to and from the Golgi apparatus

Question 14

What is the function of the Golgi apparatus

Answer 14

• proteins are modified - add sugar molecules to make glycoproteins, add lipid molecules to make lipoproteins, being folded into there 3D shape
• proteins are packaged into vesicles that are pinched off and then - stored in the cell, or moved to the plasma membrane either to be incorporated into the plasma membrane or exported outside the cell

Question 15

What is the structure of the mitochondria

Answer 15

• spherical, rod shaped or branched, 2-5 micrometres long
• they are surrounded by two membranes with fluid filled space between them, inner membrane is folded into cristae
• the inner part of the mitochondrion is a fluid filled matrix

Question 16

What is the function of the mitochondria

Answer 16

• they are the site of ATP production during aerobic respiration
• self replicating so more than one can be made if the cells energy needs increase
• they are abundant in cells where highly levels of metabolic activity take place - liver cells, synapse and between neurones where neurotransmitter is synthesised and released

Question 17

What structure of chloroplasts

Answer 17

• large organelles about 4-5 micrometres long
• they are found in plant cells and some protoctists
• surrounded by a double membrane or envelope, inner membrane is continuous with stacks of flattened membrane sacs called thylakoids which contain chlorophyll - each stack or pile of thylakoids is called a granum and matric is called the stroma
• chloroplasts contain loops of DNA and starch grains

Question 18

What is the function of chloroplasts

Answer 18

• site of photosynthesis
• the first stage of photosynthesis - light energy is trapped by chlorophyll and used to make ATP this occurs in the grana, water is also spilt to supply the hydrogen ions
• the second stage of photosynthesis - hydrogen reduces carbon dioxide and uses energy from ATP to make carbohydrates this occurs in the stroma, chloroplasts are abundant in leaf cells particularly the palisade mesophyll layer

Question 19

What is the structure of the vacuole

Answer 19

• surrounded by a membrane called tonoplast and contains fluid

Question 20

what is the function of the vacuole

Answer 20

• only plant cells have large permanent vacuoles,
• filled with water and solutes which maintain the cell stability
• when the cell is full it pushes against the cell wall this makes the cell turgid
• if all plant cells are turgid then this supports the plant especially in non woody plants

Question 21

What is the structure of lysosomes

Answer 21

• small bags formed from the Golgi apparatus, they are surrounded by a single membrane
• contain powerful hydrolytic enzymes
• abundant in phagocytic cells such as neutrophils and macrophages these can ingest and digest invading pathogens such as bacteria

Question 22

What is the function of lysosomes

Answer 22

• keep the powerful hydrolytic enzymes away and separate from the rest of the cell
• can engulf old cell organelles and foreign matter it digests them and returns thee digested components to the cell for reuse

Question 23

What is the structure of cilia and undulipodia

Answer 23

• they are protrusions from the cell and are surrounded by the cell surface membrane
• each cell contains microtubules
• they are formed from centrioles

Question 24

What is the function of cilia and undulipodia

Answer 24

• the epithelial cells line airways and have many hundreds of cilia that beat and move the mucus
• nearly all cell types have one cilium this acts as an antenna and contains receptors and allows the cell to detect signals about its immediate environment
• the one type of human cell to have a undulipodium is a spermatozoon - the undulipodium allows the spermatozoon to move

Question 25

what is the structure of ribosomes

Answer 25

- small spherical organelles about 20 nm in diameter - made of ribosomal RNA - made in the nucleolus as two separate subunits pass through the nuclear envelope into the cell cytoplasm and them combine - some remain free in the cytoplasm and some attach to the endoplasmic reticulum

Question 26

What is the function of ribosomes

Answer 26

- ribosomes bound to the exterior of the RER are mainly used for synthesising proteins that will be exported outside the cell - ribosomes are free in the cytoplasm either singly or in clusters, they are the primarily the site of assembly of proteins that will be used inside the cell

Question 27

What is the structure of centrioles

Answer 27

- the centrioles consist of two bundles of microtubules at right angles to each other - microtubules are made out of tubulin protein subunits and are arranged to form a cylinder

Question 28

What is the function of the centrioles

Answer 28

- before a cell divides the spindle made of threads of tubulin form the centrioles - chromosomes attach to the middle part of the spindle and motor proteins walk along the tubulin threads they pull the chromosomes to the opposite end of the cell Centrioles are involved in the formation of the cilia and undulipodia - before the cilia forms the centrioles multiply and line up beneath the cell surface membrane - microtubules then sprout outwards from each centriole forming a cilium or undulipodium - centrioles are usually absent from cells of higher plants but may be present in some unicellular green algae such as chlamydomonas

Question 29

what is the structure of the cytoskeleton

Answer 29

- network of protein structures within the cytoplasm - consists of rod like microfilaments made of subunits of the protein actin - polymers of actin and each microfilament is about 7nm in diameter - intermediate filaments about 10 nm in diameter - straight, cylindrical microtubules, made up of protein subunits called tubulin which are about 18-30 nm in diameter - the cytoskeletal motor proteins - myosins, kinesins and dyneins are molecular motors, they are also enzymes and have a site that binds to and allows hydrolysis of ATP as their energy source

Question 30

What are the functions of the cytoskeleton

Answer 30

- protein microfilaments within the cytoplasm give support and strength they keep the cells shape stable and allows cell movement - help substances move through the cytoplasm within the cell - they form a track along which motor proteins such as dynein and kinesin walk and drag organelles from one part of the cell to another - form a spindle before the cell divides - they enable chromosomes to be moved within the cell - microtubules also make up the cilia, undulipodia and centrioles intermediate filaments are made up of variety of proteins and they.... - anchor the nucleus within the cytoplasm - extend between cells in some tissues between special junctions this enables cell-cell signalling and allowing cells to adhere to a basement membrane stabilising tissues

Question 31

What is the structure of a cellulose cell wall

Answer 31

- cell wall of plants is on the outside of the plasma membrane and is made from bundles of cellulose fibres

Question 32

What is the function of the cellulose cell wall

Answer 32

- prevent bursting when turgid - provide strength and support - maintain cells shape - contribute to the strength and support of the whole plant - permeable and allow solutions (solute and solvent) to pass through - fungi have cell walls which contain chitin and not cellulose

Question 33

How do you make and secrete a protein

Answer 33

- the gene has the coded instruction for a protein such as insulin which is on chromatin in the nucleus, it is transcribed into a length of RNA called mRNA - many copies of MRNA are made which pass out of the nuclear envelope to the ribosomes - at the ribosomes the instructions are translated and insulin molecules are made - the insulin molecules pass into the cisternae of the RER and along the hollow sacs - vesicles with the insulin inside are pinched off from the RER and pass via microtubules and motor proteins to the Golgi apparatus - the vesicles fuse with the Golgi apparatus where the insulin protein molecules are modified for release - inside vesicles pinched off from the Golgi apparatus these molecules pass to the plasma membrane - vesicles and plasma membrane fuse and the insulin is released to the outside of the cell

Question 34

How is insulin made

Answer 34

1. mRNA copy of the instructions for insulin is made in the nucleus 2. mRNA leave the nucleus through a nuclear pore 3. mRNA attaches to a ribosome in this case attaches to the RER, the ribosome reads the instructions to assemble the protein 4. insulin molecules are pinched off in vesicles and travel towards the Golgi apparatus 6. Golgi apparatus processes and packages insulin molecules ready for release 7. packaged insulin molecules are pinched of the vesicles from the Golgi apparatus and move towards the plasma membrane 8. vesicle fuses with plasma membrane 9. plasma membrane opens to release insulin molecules outside

Question 35

Compare prokaryotic and eukaryotic cells ( similarities)

Answer 35

similar - a plasma membrane - cytoplasm - ribosomes for assembling amino acids into proteins

Question 36

Compare prokaryotic and eukaryotic cells (differences)

Answer 36

prokaryotic cells are ... - much smaller - have a less well developed cytoskeleton with no centrioles - don't have a nucleus - don't have a membrane bound organelle such as mitochondria, ER, chloroplasts or Golgi apparatus - have a wall that is made out of peptidoglycan and not cellulose - have smaller ribosomes - have naked DNA which is not wound around histone proteins but float free in the cytoplasm as a loop

Question 37

what do some prokaryotic cells also have

Answer 37

- a protective waxy capsule that surrounds the cell wall - a small loop of DNA called plasmids as well as the main large loop of DNA - flagella - this is long whip - like projections that enable them to move - different from that of undulipodia which is in eukaryotic cells - pili - small like hair projections that enable bacteria to adhere to host cells or to each other to allow the passage of plasmid DNA from one cell to another

Question 38

How do prokaryotic cells divide

Answer 38

binary fission - they do not have linear chromosomes so therefore cannot carry out mitosis - before they divide their DNA is copied so each new cell receives a large loop of DNA and smaller plasmids