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Biology - AS Level > DNA and Chromosomes > Flashcards

DNA and Chromosomes Flashcards

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1
Q

where is the DNA found in eukaryotic cells

A

in the nucleus

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2
Q

what structure does the DNA form

A

long thread like structures called chromosomes

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3
Q

what does each chromosome consist of

A

one single molecule of DNA and it associates with a protein called a histone

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4
Q

what is a histone protein

A

protein that provides structural support for a chromosome enabling the DNA to be highly coiled

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5
Q

how many chromosomes are there in a human cell

A

46 indiv and 23 pairs-called homologous pairs

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6
Q

what are alleles

A

different forms of the same gene

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7
Q

what does a chromosome carry

A

genes

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8
Q

what is a gene

A

sequence of bases on a chromosome that codes for a particular proteins
(and a functional RNA product)

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9
Q

what is the position of a gene on a chromosome called

A

gene locus

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10
Q

what is the genome

A

the entire collection of genes in an organism

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11
Q

what does the DNA look like as it is dividing

A

two chromatids joined at a central point called a centromere

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12
Q

what is the entire collection of proteins called

A

proteome

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13
Q

what are the non-coding regions of DNA called

A

introns- consiting of short sequences of bases called mini-satellites

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14
Q

what are the coding regions of DNA called

A

exons- 2-3%

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15
Q

what is the relative length of E DNA

A

large/long

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16
Q

what is the shape of E DNA

A

linear - double helix two strands twisted

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17
Q

how many molecules per cell of E DNA

A

several - species dependent

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18
Q

structure of DNA in prokaryotic cells

A

-smaller
-circular
-not associated with proteins
-1molecule per cell
-no non-coding DNA

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19
Q

what do the sequence of bases code for

A

an amino acid

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20
Q

how many bases code for one amino acid

A

3- codon/triplet

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21
Q

what do proteins make

A

enzymes-responsible for virtually all chemical reactions in cells

22
Q

how is the genetic code degenerate

A

more than one set of codons can code form one amino acid

23
Q

what to look out for in code tables

A

wether it contains uracil or thymine
U= mRNA
T= DNA

24
Q

how is the genetic code universal

A

same code used by all living organisms

25
Q

what amino acid starts every coding DNA sequence

A

methionine-AUG

26
Q

what does a triplet code for if it does not code for an amino acid

A

a stop signal

27
Q

why is the code non-overlapping

A

each base is only part of one triplet

28
Q

what are introns

A

The genome within eukaryotic cells contains many non-coding sections of DNA
Non-coding DNA does not code for any amino acids
Non-coding DNA can be found between genes, as non-coding multiple repeats
This means they contain the same base sequences repeated multiple times

29
Q

what are exons

A

coding parts of DNA

30
Q

how is the introns removed in transcription

A

splicing
eukaryotic cells transcribe the whole gene (all introns and exons) to produce pre-mRNA molecules
Before the pre-mRNA exits the nucleus the non-coding sections (introns) are removed and the coding sections (exons) are joined together in a process called splicing

31
Q

what is the structure of RNA

A

Like DNA, the nucleic acid RNA (ribonucleic acid) is a polynucleotide – it is made up of many nucleotides linked together in a long chain
Like DNA, RNA nucleotides contain the nitrogenous bases adenine (A), guanine (G) and cytosine (C)
Unlike DNA, RNA nucleotides never contain the nitrogenous base thymine (T) – in place of this they contain the nitrogenous base uracil (U)
Unlike DNA, RNA nucleotides contain the pentose sugar ribose (instead of deoxyribose)
Unlike DNA, RNA molecules are only made up of one polynucleotide strand (they are single-stranded)
Each RNA polynucleotide strand is made up of alternating ribose sugars and phosphate groups linked together, with the nitrogenous bases of each nucleotide projecting out sideways from the single-stranded RNA molecule

32
Q

what are the bonds called bwt the backbone and the pentose sugar

A

The sugar-phosphate bonds (between different nucleotides in the same strand) are covalent bonds known as phosphodiester bonds
These bonds form what is known as the sugar-phosphate backbone of the RNA polynucleotide strand
The phosphodiester bonds link the 5-carbon of one ribose sugar molecule to the phosphate group from the same nucleotide, which is itself linked by another phosphodiester bond to the 3-carbon of the ribose sugar molecule of the next nucleotide in the strand

33
Q

what are the 3 types of RNA

A

-mRNA
-tRNA
-rRNA

34
Q

what is the structure of mRNA

A

mRNA is a single-stranded molecule-linear
It is made up of a sugar-phosphate backbone and exposed unpaired bases
Uracil bases are present instead of thymine bases (which are found in DNA)

35
Q

what is the structure of tRNA

A

tRNA is a single-stranded molecule
It has a sugar-phosphate backbone
It has a folded shape -clover-leaf
There are hydrogen bonds between some of the complementary bases
Amino acids bind to a specific region of the molecule
The specific anticodon found on the tRNA molecule is complementary to a specific codon on an mRNA molecule

36
Q

what are the 2 stages of protein synthesis

A

transcription – DNA is transcribed and an mRNA molecule is produced
Translation – mRNA (messenger RNA) is translated and an amino acid sequence is produced

37
Q

what is the process of transcription

A

This stage of protein synthesis occurs in the nucleus of the cell
Part of a DNA molecule unwinds (the hydrogen bonds between the complementary base pairs break)
Catalysed by DNA helicase, like in DNA replication
This exposes the gene to be transcribed (the gene from which a particular polypeptide will be produced)
A complementary copy of the code from the gene is made by building a single-stranded nucleic acid molecule known as mRNA (messenger RNA)
Free activated RNA nucleotides pair up (via hydrogen bonds) with their complementary (now exposed) bases on one strand (the template strand) of the ‘unzipped’ DNA molecule- catalysed by RNA polymerase
The sugar-phosphate groups of these RNA nucleotides are then bonded together by the enzyme RNA polymerase to form the sugar-phosphate backbone of the mRNA molecule- phosphodiester bonds
When the gene has been transcribed (when the mRNA molecule is complete), the hydrogen bonds between the mRNA and DNA strands break and the double-stranded DNA molecule re-forms
The mRNA molecule then leaves the nucleus via a pore in the nuclear envelope

38
Q

the difference between template and non-template

A

In the transcription stage of protein synthesis, the section of the DNA molecule where the gene is located (the gene coding for a particular polypeptide) unwinds – the hydrogen bonds between the complementary base pairs break, causing the two DNA strands to ‘unzip’
Free activated RNA nucleotides then pair up with the exposed bases on the DNA molecule but only with those bases on one strand of the DNA molecule
This strand of the DNA molecule is called the template strand or the transcribed strand
This is the strand that is transcribed to form the mRNA molecule (RNA polymerase binds the RNA nucleotides together to create the sugar-phosphate backbone of the mRNA molecule)
This mRNA molecule will then be translated into an amino acid chain
The strand of the DNA molecule that is not transcribed is called the non-template strand or the non-transcribed strand

39
Q

what are the enzymes involved in transcription

A

DNA helicase
RNA polymerase

40
Q

what is important to remember about base pairing DNA to mRNA

A

T changes to U
so
A-U
C-G

41
Q

what must happen to the RNA before it is converted to mRNA

A

must be spliced = remove introns

42
Q

what is translation

A

This stage of protein synthesis occurs in the cytoplasm of the cell
After leaving the nucleus, the mRNA molecule attaches to a ribosome
In the cytoplasm, there are free molecules of tRNA (transfer RNA)
These tRNA molecules have a triplet of unpaired bases at one end (known as the anticodon) and a region where a specific amino acid can attach at the other
There are at least 20 different tRNA molecules, each with a specific anticodon and specific amino acid binding site
The tRNA molecules bind with their specific amino acids (also in the cytoplasm) and bring them to the mRNA molecule on the ribosome
The triplet of bases (anticodon) on each tRNA molecule pairs with a complementary triplet (codon) on the mRNA molecule- and hydrogen bond
Two tRNA molecules fit onto the ribosome at any one time, bringing the amino acid they are each carrying side by side
A peptide bond is then formed between the two amino acids
The formation of a peptide bond between amino acids requires energy, in the form of ATP
The ATP needed for translation is provided by the mitochondria within the cell- it is converted to adenine monophosphate and 2 Pi is released
This process continues until a ‘stop’ codon on the mRNA molecule is reached – this acts as a signal for translation to stop and at this point the amino acid chain coded for by the mRNA molecule is complete
This amino acid chain then forms the final polypeptide- then the tRNA is released and can be used again

43
Q

what enzyme catalyses’ translation

A

peptidyl transferase

44
Q

what is the first codon on every mRNA known as

A

AUG - methionine

45
Q

where does the polypeptide chain go after translation if it is going to be used in a cell

A

to the ribosome then into cytoplasm

46
Q

where does the polypeptide chain go after translation if it is going to be used outside of the cell

A

to the rough endoplasmic reticulum and then to the Golgi for further processing and packaging then to the vesicles

47
Q

at what time can 2 lots of translation occur

A

at the same time/simultaneously

48
Q

what are groups of ribosomes working together called

A

polyribosomes or polysomes

49
Q

how do nucleic acid and amino acids relate to one and other

A

A triplet is a sequence of three DNA bases that codes for a specific amino acid
A codon is a sequence of three mRNA bases that codes for a specific amino acid
A codon is transcribed from the triplet and is complementary to it
An anticodon is a sequence of three tRNA bases that are complementary to a codon
When comparing the genetic code to amino acid sequences, mRNA codons are often used
The four bases found in RNA molecules (adenine, uracil, cytosine and guanine) have the ability to form 64 different codons
The genetic code is degenerate
Multiple mRNA codons can encode the same amino acid
This means that a change in the genetic code doesn’t necessarily result in a change in the amino acid sequence
UGU and UGC both code for the amino acid cysteine
Some send important signals to the translation machinery
The START codon marks the start of the protein and therefore initiates the process of translation from the right location (this is always the amino acid methionine in eukaryotic cells, coded for by the codon AUG)
STOP codons cause translation to terminate at the end of the protein and do not code for any amino acids e.g. UAA
The genetic code is non-overlapping
Each base is only read once in the codon it is part of
The number of amino acids in a protein can be calculated using the number of coding nucleotides in the mRNA molecule and vice versa:
When given the number of coding mRNA nucleotides, divide by 3 and minus one (for the stop codon – it is best to state this in your answer too)
When given the number of amino acids, multiply by 3 and add three (for the stop codon)

50
Q

What is rRNA

A

Makes up part of the structure of ribosomes

Biology - AS Level (17 decks)

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