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BIO U3/4 > CHAPTER 1: NUCLEIC ACIDS & PROTEINS > Flashcards

CHAPTER 1: NUCLEIC ACIDS & PROTEINS Flashcards

1
Q

state the functions of the two monomers of nucleic acid

A

deoxyribonucleic acid (DNA): double-stranded helix structure built from nucleotides (sugar phosphate backbone, nitrogenous base, & phosphate group)
ribonucleic acid (RNA): single stranded helix polymer that codes & decodes genetic information for proteins.

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2
Q

state the base pairing rules for both RNA and DNA

A

DNA: A-T & C-G
RNA: A-U & C-G

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3
Q

state the structure of DNA

A
  • double stranded sugar phosphate backbone
  • base pair
  • nitrogenous base
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4
Q

state the structure of RNA

A
  • single stranded sugar phosphate backbone
  • ribose sugar
  • phosphate group
  • nitrogenous bases
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5
Q

similarities in DNA & RNA

A
  • both the molecules of DNA and RNA are formed of monomers known as nucleotides.
  • both these molecules possess four nitrogenous bases.
  • both the molecules of DNA and RNA exhibit a phosphate backbone to which attachment of bases takes place.
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6
Q

how does RNA differ from DNA

A
  • RNA has an unpaired single chain of nucleotides
  • contains the sugar ribose
  • contains uracil rather than thymine
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7
Q

definition of mRNA

A

messenger RNA carries the genetic message from the DNA from the nucleus to the ribosome (processes of transcription and translation), three nucleotides known as a codon

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8
Q

definition of rRNA

A

ribosomal RNA with specific proteins make the ribosomes in the cytosol

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9
Q

definition of tRNA

A

transfer RNA carry specific amino acids to ribosomes to be used to construct proteins. Anticodon of tRNA bind to the
complementary codon on the mRNA.

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10
Q

what is ‘universal’ in the DNA code?

A

universal – essential the same in bacteria, plants and animals. The genetic code is universal because all species use the same four bases A,T,C and G, and each base sequence codes for the same amino acid in all species.

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11
Q

what is ‘redundant’ in the DNA code?

A

degenerate/redundant: more than one sequence of nucleotides (codon) codes for the same amino acid

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12
Q

describe the steps of transcription

A
  1. RNA polymerase, attaches to a promoter sequence of DNA in the upstream region of the template strand.
  2. The double-stranded DNA of the gene unwinds and exposes the bases of the template strand.
  3. The RNA polymerase enzyme moves along the DNA template in a 3′ to 5′ direction. Nucleotides are joined to form an RNA chain.
  4. After the RNA polymerase moves past the coding region and into the downstream region of the gene, transcription stops and the mRNA molecule (pre-mRNA) is released
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13
Q

RNA processing

A

post-transcription modification: pre-mRNA to mRNA
* Once transcription has occurred, the pre-mRNA
is modified by:
* Capping of the 5’ end (methyl cap)
* Addition of a poly-A tail on the 3’ end
* Introns removed and exons are spliced together
* Then the mRNA moves into cytoplasm and ribosomes attach to the mRNA.

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14
Q

describe the steps of translation

A
  1. mRNA moves to the ribosome, where it is read in groups of three (codon) - begins at the ‘start adding amino acids’ signal
  2. Each codon corresponds to an anti-codon found on tRNA which is attached to one of the 20 amino acids
  3. The ribosomes moves along the mRNA and tRNA molecules to deliver the amino acid (attaching to the previous amino acid forming a polypeptide chain)
  4. A codon representing STOP is reached and the polypeptide is released from the ribosome
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15
Q

amino acid structure

A
  • amino group
  • carboxyl group
  • R group
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16
Q

polypeptide vs protein

A

a polypeptide is a sequence of amino acids while a protein is a sequence of amino acids with a function. Whereas one polypeptide may need to join with another to have a function = be a protein

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17
Q

protein primary structure

A

linear sequence of amino acids that are linked together - called a polypeptide

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18
Q

protein secondary structure

A

the secondary structure of proteins consists of:
* alpha helices
* beta sheets
* random coils
folding and coiling is caused by the
interaction of the R-groups

19
Q

protein tertiary structure

A

involves the way the random coils, alpha helices and beta sheets fold in respect to each other. This shape is held in place by chemical bonds - the functional structure.

20
Q

protein quaternary structure

A

the bonding of more than one
polypeptide chain

21
Q

definition of proteome

A

the complete range of proteins made by a cell
or organism - the proteome is more complex than the genome.

22
Q

describe the exons and introns in the eukaryotic gene structure

A

Exons: contain the instructions for the synthesis
of the protein (transcribed and translated)
Introns: do not contain instructions relating to the protein chain. They are transcribed in the nucleus but are cut out in RNA processing

23
Q

promoter sequence

A
  • Region of DNA on the template strand (upstream from the coding region) that controls the activity of that gene
  • One part of the promoter TATA box (rich in A and T’s)
  • Where RNA polymerase binds to initiate transcription
  • Without a functioning promoter region, transcription cannot be properly
    initiated.
24
Q

when and where are genes expressed?

A

all nucleated cells contain the same DNA but not all genes are expressed in all cells
* E.G. Pancreatic cells make insulin so the gene for insulin will be expressed
* Skin cells make collagen so the gene for collagen will be expressed

Not all genes are active throughout life
* E.G. fetal haemoglobin
* AD1 gene linked to a form of Alzheimer’s disease

Genes can be switched on or off – gene regualtion

25
Q

definition of structural genes

A

structural genes code for proteins that become part of the structure or function of cells
* E.G. (trpA, trpB, trpC, trpD, and trpE, which encodes tryptophan synthetase)

26
Q

definition of regulatory genes

A

code for proteins that control the expression of
other genes (transcription factors). Their actions determine whether other genes are active (‘on’) or not (‘off’)

27
Q

what are the two ways regulatory genes act?

A

act in 2 ways:
* Directly: Produce DNA binding proteins that bind to a region of nuclear DNA near genes to directly turn them on or off
* Indirectly: Produce signalling proteins that bind to cell receptors and trigger a series of reactions that leads to a gene being turned on or off

Homeotic(HOX) genes are ‘master’ regulatory genes that control embryonic development
* Problems with HOX genes can result in major abnormalities

28
Q

definition of operon

A

cluster of structural genes on a chromosome, (under control of a single promoter and operator) transcribed as a single unit

29
Q

definition of operator

A

a short DNA segment that provides a binding site for a repressor, so transcription cannot occur.

30
Q

what happens in the presence of tryptophan?

A
  • trp binds to the repressor protein causing a configurational change in its shape, allowing it to be active.
  • this allows the repressor to bind at the operator.
  • RNA polymerase unable to bind to the promoter and transcription does not occur. The operon is OFF
31
Q

what happens in the absence of tryptophan?

A
  • The repressor (inactive form) unable to bind to the operator
  • RNA polymerase can bind to the promoter and start transcription of
    the structural genes
  • The operon is ON
32
Q

describe condensation polymerisation

A

smaller molecules or monomers react with each other to form larger structural units (usually polymers) while releasing by-products such as water or methanol molecule.
e.g: the polypeptides of amino acids are formed together w/ the by-product of water

33
Q

explain why the shape of a protein is important to its function

A

the structure of proteins is important as the shape of a protein allows it to perform its particular/ specific role or function in a cell or body structure

34
Q

summarise the role of the nucleus in the production and export of proteins

A
  • Houses chromosomes, made of chromatin (DNA, the genetic material and proteins)
  • Contains the nucleolus, where ribosomal sub-units are synthesised and assembled
  • Nuclear pores regulate entry and exit of materials including proteins and RNA.
35
Q

summarise the role of the smooth/rough endoplasmic reticulum in the production and export of proteins

A
  • Smooth endoplasmic reticulum is involved in the synthesis of lipids, metabolism of carbohydrates, calcium storage, and detoxication of drugs and
    poisons.
  • Rough endoplasmic reticulum is involved in the synthesis of specific proteins from bound ribosomes.
36
Q

summarise the role of the transport vesicle in the production and export of proteins

A

The function of transport vesicles inside a cell is to move molecules around the cell. Transport vesicles are small spheres of membrane. They may contain proteins or other molecules in the membrane or inside the vesicle.

37
Q

summarise the role of the golgi apparatus in the production and export of proteins

A
  • Modifies, sorts, tags, packages and distributes proteins to be secreted via vesicles.
38
Q

summarise the role of the secretory vesicle in the production and export of proteins

A

Secretory vesicles play an important role in moving molecules outside of the cell, through a process called exocytosis. They are crucial for healthy organ and tissue function. For example, secretory vesicles in the stomach will transport protein-digesting enzymes to help break down food.

39
Q

summarise the role of the plasma membrane in the production and export of proteins

A

The structural boundary that controls the entry of raw materials into the cell, such as amino acids, the building blocks of proteins

40
Q

describe the protein secretatory pathway

A
  1. The nucleus codes for the protein (makes mRNA) which goes to the) ribosome on the rough endoplasmic reticulum.
  2. The ribosome uses the mRNA code to make a protein which is then folded and modified in the rough endoplasmic reticulum.
  3. Placed into a transport vesicle the protein then moves to the Golgi Apparatus where it is further modified before being packaged into a secretory vesicle for export out of the cell (At the cell membrane via exocytosis)
41
Q

define exocytosis

A

exocytosis is the process that enables the secretion of proteins out of the cell as the final step in the protein secretory pathway. The intracellular membranes are fluid and bud off to form vesicles that fuse with the plasma membrane and release their contents into the extracellular environment.

42
Q

what are the important parts of an eukaryotic gene? (left to right)

A

upstream enhancer -> promoter -> TATA box -> 5’ UTR -> Coding region -> 3’ UTR

43
Q

describe repression - gene regulation

A

involves the trp repressor protein, expressed by the regulatory gene, in its active form (bound to two tryptophans) binding to the operator sequence and blocking the initiation of transcription

44
Q

describe attenuation - gene regulation

A
  • Prevents the completion of transcription - the leader segment features two adjacent trp codons, and when transcribed has regions that undergo base pairing to form hairpin loops.
  • When the levels of tryptophan are high and the repressor protein is not bound to the operator region, the ribosome does not pause at the two adjacent trp codons and a different hairpin loop forms, causing transcription to be terminated.
  • The consequence is that the ribosome detaches from the short (attenuated) mRNA transcript strand, transcription stops prematurely.
  • Attenuation of the trp operon is made possible in prokaryotes because transcription and translation in prokaryotes take place very close to each other in the cytoplasm, as the two processes are not separated by a nuclear membrane and the five structural genes are not expressed

BIO U3/4 (7 decks)

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