Topic 4A - DNA, RNA and Protein synthesis

Question 1

Is DNA stored differently or the same in different organisms?

Answer 1

It is stores different in different organisms

Question 2

How do eukaryotic cells store DNA?

Answer 2

They store DNA as linear chromosomes - thread-like stuctures each made up of one long molecule of DNA. These are usually found in nucleus

Question 3

Describe the structure of a eukaryotic linear DNA molecule (chromosome)?

Answer 3

1. They are really long, so its wound up to fit in nucleus
2. They are wound around proteins called histones (which help support DNA)
3. DNA (with protein) is coiled up very tightly to make compact chromosome (DNA double-helix)

Question 4

What kind of DNA to mitochondria and chloroplasts have?

Answer 4

They have DNA similar to prokaryotic cells as its circular and shorter than DNA molecules in nucleus.
- This type of DNA is not supported by histone proteins

Question 5

What is the difference between prokaryotic and eukaryotic DNA?

Answer 5

1. Prokaryotic DNA is shorter and circular

2. Prokaryotic DNA isnt wound around histones - it condenses to fit in cell by supercoiling

Question 6

What is a gene?

Answer 6

a sequence of DNA bases that codes for either a polypeptide or functional RNA (RNA molecules, other than mRNA, that perform special tasks during protein synthesis e.g. tRNA and ribosomal RNA)

Question 7

What determines the order of amino acids in a polypeptide?

Answer 7

The order of bases in a gene

Question 8

How is each amino acid coded?

Answer 8

They are coded for by a sequence of 3 bases in a gene called a triplet

Question 9

What is the 1st stage of making a polypeptide (1st stage of protein synthesis)?

Answer 9

DNA is first copied into messenger RNA

Question 10

What is a genome?

Answer 10

The entire DNA of an organism

Question 11

What is a proteome?

Answer 11

The full range of proteins that a cell is able to produce

Question 12

What are introns?

Answer 12

They are the sections of a gene that dont code for amino acids

Question 13

What are exons?

Answer 13

They are the sections of a gene that do code for amino acids

Question 14

Do introns affect the order of amino acids?

Answer 14

No as they are removed during protein synthesis

Question 15

What is the purpose of introns?

Answer 15

Unknown

Question 16

What are non-coding repeats?

Answer 16

They are regions of multiple repeats outside of genes e.g. CCTTCCTTCCTT
- They dont code for amino acids either

Question 17

What forms do genes exist in?

Answer 17

in the form of alleles

Question 18

What does it mean if the order of bases in every allele is slightly different?

Answer 18

It means that they code for slightly different versions of the same polypeptide e.g. the gene that determines blood type exists as one of 3 alleles - O, A and B

Question 19

How many pairs of chromosomes do humans have in total?

Answer 19

23

Question 20

What are homologous pairs?

Answer 20

Pairs of matching chromosomes that are the same size, and have the same genes, but could have different alleles

Question 21

How would you know if alleles codes for the same characteristic in a homologous pair?

(DIAGRAM)

Answer 21

They should be found at the same fixed position (locus) on each chromosome

Question 22

What is the main difference between RNA and DNA?

Answer 22

1. RNA is a single polynucleotide strand, whilst DNA is a double helix
2. It contains uracil, instead of thymine

Question 23

Describe the structure and function of mRNA

DIAGRAM

Answer 23

Structure:

• It is a single polynucleotide strand
• In mRNA, groups of 3 adjacent bases make up a codon/triplet code/base triplets

Function:
- Carries the genetic code from DNA to ribosomes, where its used to make a protein during translation

Question 24

Describe the structure and function of tRNA

DIAGRAM

Answer 24

Structure

• a single polynucleotide strand folded into a clover shape (Hydrogen bonds between base pairs hold molecule in clover shape)
• Has a specific sequence of 3 bases at 1 end called anticodon
• Has an amino acid binding site at other end

Function:
- Carries amino acids, used to make proteins, to the ribosomes

Question 25

Where does transcription take place in: - Eukaryotic cells? - Prokaryotic cells?

Answer 25

Eukaryotic cells - Nucleus | Prokaryotic cells - cytoplasm

Question 26

Describe steps 1-3 of transcription *DIAGRAM*

Answer 26

1- Hydrogen bonds between DNA strands breaks, separating strands, and DNA molecule uncoils at that point, exposing some of the bases 2. One strand is used as template to make mRNA copy 3. Specific, complementary base pairing allows mRNA strand to be complementary to DNA template strand 4. RNA polymerase attaches to DNA double-helix at the beginning of gene and joins nucleotides together. 5. Hydrogen bonds between uncoiled strands of DNA re-form after RNA polymerase has passed, forming double-helix again 6. When enzyme reaches particular sequence of DNA called a stop signal, it stops making mRNA and detaches from DNA 7. Splicing occurs and mRNA moves out of nucleus through nuclear pore and attaches to ribosome

Question 27

What is pre-mRNA?

Answer 27

mRNA strands containing introns and exons. | - In eukaryotes, introns and exons are copied into mRNA during transcription

Question 28

What is splicing?

Answer 28

A process that occurs in the nucleus in eukaryotes, where introns are removed and exons are joined together - forming mRNA strands - mRNA then leaves nucleus to the ribosome

Question 29

Does splicing take place in prokaryotes?

Answer 29

No as prokaryoes have no introns, so theres no need

Question 30

Where does TRANSLATION occur in: - Eukaryotes? - Prokaryotes?

Answer 30

In both, it occurs at the ribosomes in the cytoplasm?

Question 31

Describe steps 1-3 of TRANSLATION *DIAGRAM*

Answer 31

1. mRNA attaches to ribosome and tRNA molecules carry amino acids to it. ATP provides energy needed for bond between amino acid and tRNA to form 2. tRNA (carrying amino acid), with anticodon complementary to 1st codon on mRNA, attaches to it mRNA by specific base pairing. 3. 2nd trRNA attaches itself to next codon in same way 4- 2 amino acids attached to tRNA molecules are joined by peptide bond. tRNA moves away, leaving it alone 5- 3rd tRNA binds to next codon on mRNA. It's amino acid binds to first two (amino acids) and 2nd tRNA moves away 6- Process continues to produce chain of linked amino acids (polypeptide chain) until theres a stop signal on mRNA molecule 7- Polypeptide moves away from ribosome

Question 32

What is the main point of: - transcription? - translation?

Answer 32

Transcription: To produce mRNA copy of gene, from DNA Translation: To join up amino acids to make polypeptide chain, following sequence of codons carried by mRNA

Question 33

Whats another word for protein synthesis?

Answer 33

Polypeptide synthesis

Question 34

What is the 'genetic code'

Answer 34

The sequence of base triplets in mRNA which code for specific amino acids

Question 35

What does it mean if the genetic code is 'non-overlapping'?

Answer 35

Non-overlapping: in genetic code, each base triplet is read in sequence, separate from triplet before it and after it and base triplets dont share their bases

Question 36

What does it mean if the genetic code is 'degenerate'?

Answer 36

Degenerate: There are more possible combinations of triplets than there are amino acids (20 acids but 64 combos). This means that some amino acids are coded for by more than 1 base triplet e.g. Tyrosine can be coded for by UAU and UAC

Question 37

What does it mean if the genetic code is 'universal'?

Answer 37

Universal: The same specific base triplets code for the same amino acids in all living things

Question 38

look at quesions on interpreting data ABOUT NUCLEIC ACIDS

Answer 38

*look in book*

Question 39

look at questions on interpreting data about THE ROLE of nucleic acids

Answer 39

*look in book*