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JC bio > cell structure > Flashcards

cell structure Flashcards

1
Q

What are the organelles which are visible under the light microscope?

(8 organelles) 
Not
My 
4Cs
For 
School
A 
Nucleus 
Mitochondria
Chloroplast 
Cell Wall
Cell Membrane 
Central Vacuole 
Flagella 
Starch Grains
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2
Q

Describe the main identifying features of the nucleus
+

Function of the Nucleus

A

FEATURES
• Prominent, spherical** organelle in eukaryotic cell
•Surrounded by a nuclear envelope** (a double membrane) which is perforated with nuclear pores** & continuous with RER**
•Contains the nucleolus* & chromatin*

ROLE:
•To contain the hereditary material** (DNA)
•To control cell activities ** by regulating protein synthesis**

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3
Q

What is the structure and function of the nuclear envelope?

extension:
role of nuclear pores

A

It is perforated by numerous nuclear pores which allow the passage of the mRNA coding for peptide /protein out of the nucleus for translation to peptide in the ribosomes

(extension)
role of nuclear pores:
-regulate the movement of molecules from the nucleus to the cytoplasm or from the cytoplasm into the nucleus
- allow transport of mRNA, tRNA, ribosomal subunits out of the nucleus
- movement of enzymes (DNA Pol, RNA pol), nucleotides (dNTPs), and proteins (histones, ribosomal proteins, transcription factors) into nucleus

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4
Q

What is the structure and function of the nucleolus

A

Structure:
•Non-membranous,sphere/s within nucleus
•Contains large amounts of DNA, RNA & protein

Function:
•To synthesize rRNA, a component of ribosomes
•Site of assembly of rRNA & proteins into large & small ribosomal subunits required for TRANSLATION*****

+++ ( if question has more mark)

  • rRNA of the small ribosomal subunit has mRNA binding site
  • part of the rRNA molecule, peptidyl transferase in the large ribosomal subunit has the ability to catalyse peptide bind formation
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5
Q

What is the structure and function of chromatin?

(link to chromatin remodeling complex:
protein complexes which alter the structure of nucleosomes temporarily which can cause DNA to be more tightly coiled around the histones)

A

•Hereditary material of the cell
•Are thin, elongated threads of DNA coiled around histone proteins
•2 types of chromatin are present
1.Euchromatin (lightly stained, transcriptionally active, exists in a diffused, extended state)
2.Heterochromatin(darkly stained, transcriptionally inactive, usually found along the edge of nucleus).

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6
Q

What is the structure and function of RER?

A

Structure:
•A network of membranous flattened** sacs called cisternae *
•Has ribosomes* bound to the outer surface
•Continuous with the outer membrane of the nuclear envelope*

Function:
• contains ribosomes which are the site of synthesis of proteins
•To allow proteins to fold* into their native conformation* in the cisternal space*& glycosylate *them
• To transport proteins** which are synthesised by the ribosomes** on its surface to the Golgi apparatus via transport vesicles**

tut ans: 
function of RER --> protein synthesis by ribosomes studded on membrane; formation of vesicles

note: (require ATP)

KEYWORDS;
- RER+ ribosomes***

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7
Q

What is the structure and function of SER?

A

Structure:
•A network of membranous tubular sacs called cisternae
•Lacks ribosomes on the outer surface

Function:
- SER contains many embedded enzymes that catalyse the synthesis of a variety of carbohydrates and lipids
•To synthesise lipids (e.g. phospholipids, cholesterol and steroid hormones) and carbohydrates
•To detoxifiy drugs &poisons(Thus SER abundant in liver)
- SER in muscle cells store Ca2+

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8
Q

What is the structure and function of Golgi Apparatus?

note:
vesicles that fuse with the ‘cis’ face of the GA come from
1. RER carrying the protiens
2. SER carrying lipids or cabohydrates

A

STRUCTURE:
•Membrane-bound flattened sacs called cisternae & associated Golgi vesicles

•Consists of ‘forming’/‘cis’ face where new cisternae are being formed by fusion of transport vesicles from ER & a ‘mature’/‘trans’ face from which Golgi vesicles continuously bud off.

FUNCTION: ( glycosylate, modify, sort,package,target)
•Glycosylation** where carbohydrates are added to proteins and lipid to form glycoproteins and glycolipids respectively
•To modify* existing glycoproteins and glycolipids * by modifying/cleaving the existing sugar chains
•To sort and package** proteins into different vesicles and target ** the proteins to different parts of the cell or for secretion** out of cell
•Formation of lysosomes** which contain hydrolytic enzymes within them
•To synthesise polysaccharides such as pectin which is transported in vesicles to the cell membrane.

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9
Q

What is the structure and function of the lysosome?

A

Structure :
•Membranous sac containing hydrolytic enzymes

Function :
•To digest material** taken in by the cell by endocytosis** (phagocytosis)
•To release enzymes from cells by exocytosis for extracellular digestion
•To digest unwanted or worn-out organelles(autophagy)
•To self-destruct a cell after its death (autolysis)

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10
Q

What is the structure and function of the mitochondrion?

A

Structure:
•Spherical or rod shaped structures surrounded by a double membrane
1. the outer membrane is smooth
2. the inner membrane is highly convoluted with infoldings called cristae
•Between the membranes is the intermembrane space
•Cristae project into semi-fluid matrix containing circular DNA, 70S ribosomes, phosphate granules & enzymes for aerobic respiration
•ATP synthase complex on inner membrane projects into matrix

Main identifying features (tut qn)
- double-membrane envelope; inner membrane folded to form cristae

Function:
Site of aerobic respiration where ATP synthesis occurs

STRUCTURE: FUNCTION
- inner mitochondrial membrane folded and hence increases surface area for oxidative phosphorylation

  • mitochondrial matrix is the site of the link reaction and the krebs cycle
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11
Q

What are the structures and functions of the Chloroplast?

A

Structure:
•Lens-shaped structure surrounded by a double membrane
•Within the chloroplast is an internal membrane system which consists of flattened sacs called thylakoids(a stack of thylakoids = granum)& intergranal lamella
•Fluid within chloroplast surrounding the grana is called stroma(contains circular DNA, 70S ribosomes, enzymes& starch grains)
•Chlorophyll molecules are located on the thylakoid membrane
•ATP synthase complex on thylakoid membrane project into stroma

Function:
•Chloroplasts contain chlorophyll which convert solar energy to chemical energy through photosynthesis via
1) Site of light-dependent reactions(i.e. cyclic & non-cyclic photophosphorylation) which occurs in the thylakoid membrane
2) Site of light-independent reactions (i.e.Calvin cycle) which occurs in the stroma

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12
Q

What are the structures and function of ribosomes

A

Structure:
•Consists of a small & a large subunit
•Each subunit is made up of protein& rRNA is assembled in the nucleolus
•May be found either freely floating in the cytosol or bound to ER
•The small & large subunit only come together during translation

Function:
•Act as the site for protein synthesis

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13
Q

What are the structures and functions of the centrioles?

A

Structure:
•A pair of hollow cylinders made up of 9 triplets of microtubules* (hollow tubes made of the protein tubulin) each
•The two rod-like cylinders are positioned at right angles to each other
•Found in a region called the centrosome ** which is the microtubule organising centre (MTOC)

Function:
•To act as microtubule organising centre(MTOC) during spindle formation in cell division
•Determine the polarity of the cell

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14
Q

What organelles are part of the endomembrane system?

A
  1. Nuclear envelope
  2. SER and RER
  3. Golgi Apparatus
  4. Lysosomes and vesicles

note:
mitochondrion and chloroplast are NOT part of the endomembrane system

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15
Q

What is the pathway of the DNA in the endomembrane system?

A
  1. DNA is transcribed in the nucleus to mRNA
  2. mRNA leaves the nucleus via the nuclear pore
  3. mRNA translated into polypeptides on the ribosomes of the RER
  4. Polypeptides enter the lumen of the cisternae of the RER where it undergoes modification
  5. Transport vesicles buds off the RER and carry the proteins to the Golgi apparatus
  6. vesicle fuses with the ‘cis’ face of the GA and the proteins undergo further modification(e.g. glycosylation), sorting and packing
  7. A secretory vesicle containing the protein will bud off from the ‘trans’ face of the GA and are directed to the cell surface membrane by microtubules where the vesicle membrane fuses with the cell surface membrane, releasing the protein by exocytosis

note: microtubules direct the movement of the transport vesicle to the GA and the secretory vesicle to the cell surface membrane

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16
Q

What are the 3 parts of the Cell Theory

A
  1. Cells are the smallest unit of life
  2. All cells come from pre-existing cells
  3. Living organisms are composed of cells
17
Q

What are the roles of the vesicles that are formed at the maturing face of the golgi body

  • what are the vesicles?
  • roles?
A
  1. Lysosomal vesicles
    F: contains hydrolytic enzymes and fuses with vesicles formed by endocytosis to digest the contents in the vesicles
  2. Secretory vesicles
    F: fuses with the cell surface membrane to release contents to the external environment via exocytosis upon receiving signal
18
Q

Describe how peptides such as ADH present in the cisternae of the RER are secreted out of the cell

(STANDARD ANS: 4m)

A
  1. transport vesicles containing ADH pinch or bud off from rough endoplasmic reticulum
  2. the ADH protein is transported to the cis face of the Golgi apparatus where it undergoes further modification and processing (e.g. glycosylation)
  3. Upon processing, secretory vesicles bud off from the trans face of the GA and are directed to the cell surface membrane by microtubules
  4. where the vesicle membrane fuses with the cell surface membrane emptying contents by exocytosis

KEYWORDS:

  • RER
  • GA
  • vesicles bud off frm trans face of GA
    • MICROTUBULES
  • fuses with CSM
  • EXOCYTOSIS***
19
Q

Differentiate membrane bound oraganelles to single membrane and double membrane

  1. golgi apparatus
  2. nucleus
  3. lysosome
  4. mitochondria
  5. vacuoles
  6. ER
A

Single membrane :

  • vacuoles
  • ER
  • GA
  • lysosomes

double membrane:

  • nucleus
  • mitochondria
20
Q

Explain the importance of the division of mitochondria for cells in the root tips of the thale cress[2m]

A
  1. As cells grow, more energy in the form of ATP is required thus require more mitochondria
  2. More mitochondria are produced that are needed for new cells when cell divides
  3. Divison of mitochondrion produce new mitochondria to replace old and damaged mitochondria
21
Q

2019 H2 Biology A level Paper 3(b)Explain the roles of the nuclear envelope in the functioning of a eukaryotic cell. [10]

A
  1. Nuclear envelope encloses the cell’s genome / DNA and protects the genome from reactions that are occurring in the cell;
  2. It allows for compartmentalisation to occur, spatially separating transcription* in the nucleus from translation* in the cytoplasm;
  3. This allows the formation of unique environments for these processes involving enzymatic reactions reactions;
  4. The nuclear envelope serves as a barrier to large, polar and charged molecules, allowing only the selected molecules to move in and out of the nucleus via the nuclear pore*;
  5. This allows for localisation of enzymes and substrates in the same compartment so that reactions can take place more efficiently;
  6. The nuclear pores in the nuclear envelope allow for the diffusion of ribonucleoside triphosphate and the import of enzymes/proteins such as RNA polymerase* into the nucleus to allow for transcription*;
  7. Nuclear pore complexes recognises the 3’ poly-A tail* and the 5’-methylguanosine capon mature mRNA,
  8. ensuring that only mature mRNA is exported out of the nucleus for translation* in the cytoplasm;
  9. The nuclear pores also allow for the import of ribosomal proteins*;
  10. so that ribosomal proteins and rRNA* can assemble to form ribosomal subunits* in the nucleolus*;
  11. Assembled ribosomal subunits are then recognised for export* out of the nucleus into the cytoplasm

JC bio (16 decks)

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